Copyright 2015 Integrated Environmental Solutions Limited. All rights reserved.

Transcription

1 Field User Guide IES Virtual Environment Copyright 2015 Integrated Environmental Solutions Limited. All rights reserved. No part of the manual is to be copied or reproduced in any form without the express agreement of Integrated Environmental Solutions Limited.

2 Contents 1. Introduction Menus File Menu New Project Open Project Bridge In Import V.10, V.11 Project Save Project Save Project As Print Output Print Drawing Recent File List Exit Edit Menu Add Circuit Add Board Delete Edit Find Node Reference Design Data Predefined Data Loads Data View Menu Zoom In Zoom Out Zoom All Refresh Axis Lock Export DXF Print Drawing Grid Font Scale Dynamic Scroll Quick Draw Fence Overlap Database Menu Devices Cables Database Path Calculations Menu Network Calculations Single-Circuit Calculation CostPlan Output Review Menu Input Data Messages Equipment Load Balance General Load Summary Fixed Schedules Customised Schedules Key to Schedules Equipment Analysis Load Schedule Distribution Equipment Schedule Device Schedule VE 2015 Field 2

3 Cable Schedule Abbreviations and Codes Output File Help Menu Contents Help on Help About Tool Buttons Main Toolbar Status Bar Selection of Boards and Circuits Program Size Limits Voltage Drops Customised Schedules Calculation Methods Load Summation General Connected Load Design Load on Final Circuits Design Load on Distribution Circuits Design Current Neutral Current Device Selection/Checking Basic Factors Design Current Starting Current Inrush Current Discrimination Standard Circuits Ratings Set by User Fused Connection Units Socket Circuits Cable Sizing/Checking Basic Factors Current-carrying Capacity Circuit Voltage Drop Short Circuit Earth Fault Indirect Contact Maximum Grouping Maximum Length k-factors Standard Data Used in the Program Protective Device Data Standard Data Discrimination Between Fuses Device Selection on Motor Circuits BS1362 Fuses s-factors Conductor Data Cable Types Impedances Motor Data Customised Schedule Data VE 2015 Field 3

4 1. Introduction Field is a program for the design and analysis of electrical installations in accordance with BS 7671, Requirements for Electrical Installations (formerly the 16th. Edition of the IEE Wiring Regulations), with Amendment No. 1, All references to BS 7671 refer to that edition. Field assists at all stages of a design, from provisional, with only basic network and load details, to final, with details of all final circuits and including spare capacity and diversity. However, it is merely a design tool; all major decisions are left to the engineer/user, such as the types of protective devices or cables to use and the setting of voltage-drop limits for the various sections of the installation. VE 2015 Field 4

5 2. Menus The menu bar has the following options: File, Edit, View, Database, Calculations, Review, and Help. Each of these is described in detail in this section File Menu New Project The New Project command allows a new Field project to be created. On selecting this option, a standard Windows New Project dialogue box will appear. Use this dialogue box to browse through the structure of your computer system to where you wish to locate your Field project. Enter the required *.fpr file name and click on the Save button. VE 2015 Field 5

6 The new Field document will be opened and all pull-down menus on the menu bar will become active. Since you are opening a new project, the Design Data dialogue box will be displayed to remind you to edit the design data (see Design Data). If you had a project open already before you selected this command, the existing project will be closed. You can save a project using the Save command. Note if an existing project named seed.fpr exists in the Field folder below where Field.exe was installed, this is used to seed the new project. You may use this facility to help you make a quicker start on every new project, by defining your typical design data and predefined data in a project, and copying it to the correct area, renaming it to seed.fpr. A sample seed project named seed1.fpr is provided for you. To use this, simply rename it to seed.fpr. (It is deliberately named differently to prevent accidentally overwriting your seed.fpr if you install a new version of Field.) The caption now shows the name of the Field project file name on the title bar followed by the name of the program, e.g. c:\demo\fldtrnex.fpr IES Field. VE 2015 Field 6

7 Open Project The Open Project command allows you to read an existing Field project that has the extension.fpr. A standard Windows Open File dialogue box will appear. Use this dialogue box to browse through the structure of your computer system, select the required.fpr file and click on the Open button. The existing Field document will be opened and all pull-down menus on the menu bar will become active. Since you are opening an existing project, the Design data dialogue box will not be displayed. If you had a project open already before you selected this command, the existing project will be closed. You can save a project using the Save command. Again, the caption now shows the name of the Field project file name on the title bar followed by the name of the program, e.g. c:\demo\fldtrnex.fpr IES Field Bridge In The Bridge In facility allows you to locate and open files created by bridging out from InterFacet ELECTRICAL or from BSE. These are currently in the older *.f16 format, with all the actual data stored in separate files in a Field folder below the *.f16 file. Select a *.f16 file using the standard Windows Open File dialogue box, and press Open. The old-style *.f16 file and all its associated data files will be converted to a new-style Field project file Import V.10, V.11 Project The Import V.10, V.11 Project facility allows you to locate and open files in the older *.f16 format, with all the actual data stored in separate files in a Field folder below the *.f16 file. This is the format used in versions 10 and 11 of Field. Select a *.f16 file using the standard Windows Open File dialogue box, and press Open. The old-style *.f16 file and all its associated data files will be converted to a new-style Field project file. Note this is exactly the same as Bridge In because the format created by bridging out is the same Save Project You can use this command to save the current *.fpr project file at any time under the existing name, without closing the project. VE 2015 Field 7

8 Save Project As You can use this command to save the current *.fpr project file at any time under a new name and location on your computer system. On selecting this option, a standard Windows Save As dialogue box will appear. Use this dialogue box to browse through the structure of your computer system to where you wish to locate your Field project. Enter the required *.fpr file name and click on the Save button Print Output This option allows you to print the output file in its current state, whether or not you have saved it. The printer dialogue box will default to Landscape for this option. Note the output file is temporary and will be deleted when you close Field. To keep a permanent copy of the output file it must be saved. See Review > Output File for how to do this Print Drawing This option allows you to print the part of the drawing that is visible in the Graphics window. If you wish to print the complete network you would need to ensure that it is all visible first by selecting the View > Zoom All menu option. The printer dialogue box will default to Landscape for this option Recent File List These 4 options list the 4 most-recently used projects as a convenience. Selecting one of these is the same as using the Open Project option and finding the file Exit This command exits from Field. If you have made any changes to the *.fpr file, you will be given the option to save the amended file. VE 2015 Field 8

9 2.2. Edit Menu Add Circuit Use this command to add a new circuit to the drawing. After pressing the button the prompt will change as shown in the status bar below. Move the cursor to the point from which you want the circuit to start (the NEAR node). This may be anywhere on the blank space (to place a disconnected circuit), or on one of the outgoing ways (FAR node) of a board that is already placed (in more usual circumstances). In the former case a new node number will be used, and in the latter case the node number will be picked up from the board. The cursor will automatically detect the proximity of the slot and snap to it. Click the mouse and the VE 2015 Field 9

10 start point will be fixed. In this example a circuit is being placed on the yellow slot of way 6 on the board MSB. Note at any stage you may press the right mouse button to cancel placement. The prompt then changes as shown below to ask you to drag the other end of the circuit. Move the cursor to the point at which you want the circuit to end (the FAR node). Again, this may be a point either anywhere in the blank space or on the feeder area (NEAR node) of a board that is already placed (anywhere along the bottom of the board). In the former case a new node number will be used, and in the latter case the node number will be picked up from the board. The cursor will automatically detect the proximity of the feeder area and snap to it. Click the mouse and the end point will be fixed. In this example the circuit is to be unconnected at the far end. The circuit is now placed. Note that it now also appears in the text list above the graphics area. If you have made a previous circuit the default for new circuits, the circuit will pick up all of the data from that previous circuit, except of course for the way number, phase, and node numbers (see Edit for details of how to do this). VE 2015 Field 10

11 Add Board Use this command to add a new board to the drawing. After pressing the button the prompt will change as shown in the status bar below. Move the cursor to the point from which you want the board to be fed (the NEAR node). This may be anywhere on the blank space (to place a disconnected board), or on the far end (FAR node) of a circuit that is already placed (in more usual circumstances). In the former case a new node number will be used, and in the latter case the node number will be picked up from the circuit. The cursor will automatically detect the proximity of the end of the circuit and snap to it. Click the mouse and the feed point will be fixed. In this example a board is being placed on the end of the new circuit. Note at any stage you may press the right mouse button to cancel placement. The prompt then changes as shown below to ask you to drag the other end of the board to select its orientation. VE 2015 Field 11

12 This allows you to drag the board into a horizontal or vertical orientation. If the direction from the start point to the cursor is more vertical than horizontal, the board is oriented vertically; otherwise it is oriented horizontally. Click the mouse and the orientation will be fixed. In this example the board is to be represented vertically to show a busbar. The board is now placed. It now also appears in the text list above the graphics area. Note the FAR node of the board is always set equal to the NEAR node plus 1. If you have made a previous board the default for new boards the board will pick up all of the data from that previous board, except of course for the node numbers (see Edit for details of how to do this) Delete Use this command to delete all the circuits or boards that have been selected. You will be prompted to confirm the action. Note to select boards or circuits for deleting see Selection of Boards and Circuits. VE 2015 Field 12

13 Edit Use this command to edit the circuit or board that has been selected. Only one item must be selected for editing. To select boards or circuits for editing see Selection of Boards and Circuits. The dialogue box that appears now depends on whether it is a circuit or a board Circuit When you are editing a circuit the Edit Circuit dialogue box appears. This has a caption to indicate which circuit is being edited and eight tabs. One useful feature to note is that the tab that was active when this dialogue box was last closed is reactivated the next time it is opened. The General Tab This allows you to enter general data for the circuit. Way Number Isolated Description Phase Route Length Effective Length Enter the number of the way from which this circuit is fed. (Not used at present) Toggle this on if you wish this circuit and all boards and circuits downstream of it to be isolated from the source of power. Enter a description of this circuit. It is for information only and will appear on certain output schedules. Select a phase for this circuit. Enter the route length for this circuit. This is not needed on final circuits because Field will attempt to calculate a maximum length if it is set to zero. This will default to the route length. Enter a different value if you know that, from the VE 2015 Field 13

14 for Voltage Drop Length to Busbar Take-off Essential Circuit Sub-contactor? Comments Diversity (%) Make Default distribution of loads, the voltage drop would be over calculated by assuming that all of the loads are at the far end of the circuit. E.g. if the loads are evenly distributed along the circuit, the effective length is half the route length. If the feeding board is a busbar with significant impedance, the calculation of voltage drops and fault currents will be more accurate if you enter the length along the feeding board from the point where the board itself is fed to the point where this circuit is taken off. The busbar impedances are entered elsewhere, in the Edit Board dialogue box for the feeding board. Toggle this on if you wish. It is for information only and will appear on certain output schedules. Enter comments if you wish. It is for information only and will appear on certain output schedules. Enter diversity to apply to upstream load if circuit load is not always drawn. Press this button to make this circuit the default for any circuits you subsequently add to the network. This is designed for speeding up data entry by allowing you to place a typical circuit, edit it to requirements, and then make it the default for any future circuits. Note only a pointer to this circuit is stored; therefore changes you make to this circuit after making it the default will also be made to the default. The Circuit Tab This allows you to enter further details about the layout of this circuit. It is deliberately the same as the Circuit tab in the Predefined Data dialogue box (see Predefined Data), because the items defined there may be used here if desired. VE 2015 Field 14

15 Maintain Link to Predefined Data Predefined Circuit Details Name Description Protective Device Protective Device Rating (A) Voltage Drop Limit Within the Circuit (% or V) Overall Voltage Drop Limit (% or V) Ambient Temperature ( C) Configuration Standard Circuit Paste Settings Reset Settings Edit Settings Adjustable Device Settings If you select one of the predefined circuit layouts you may choose whether to maintain a link to it. If you do, and you subsequently re-edit the predefined circuit layout, the changes will be reflected in this circuit and any other circuit that has maintained a link to it. If you do not, the link is broken and the data is embedded instead If you have predefined any circuit layouts these will be available for selection here to speed up the process This read-only box shows the name of the predefined layout selected This read-only box shows the description of the predefined layout selected Select a device to use on this circuit (use the special option if none is required) Select a rating for this device if you wish to fix it, or 0 if you wish Field to calculate the minimum rating required. Set a limit for the voltage drop from one end of this circuit to the other. This will be in % of the supply voltage, or in volts, depending on what you chose in the Design Data dialogue box (see Design Data). Use this figure on various circuits to get Field to calculate sizes that satisfy the OVERALL voltage drop limits. The upper limit is 4%. Set a limit for the overall voltage drop from the nominal voltage at the supply to the end of this circuit. This must include the voltage drop at the supply which you entered in the Design Data dialogue box (see Design Data). BS7671 says that 4% or less, not including the supply voltage drop, will be deemed to satisfy the voltage drop requirements, so the upper limit is 4% plus the supply voltage drop. See also above for units Enter the ambient air temperature around this circuit under normal running conditions. Select Ring for a ring circuit, Radial for a radial circuit, or Spare if the circuit is to be kept spare for future needs (therefore not wired up yet). Note that distribution circuits must be radial Select a standard circuit layout from of the 15 th. Edition if you wish to use one, or None otherwise. Cannot be used on Distribution circuits. (Adjustable devices only.) Use this button to paste in the device settings for the adjustable device that were edited and copied using the Edit Settings button below. Note that the device and rating must match that for which the settings were edited and copied. (Adjustable devices only.) Use this button to clear the device settings for the adjustable device. After this the device will revert to its default settings when used on this circuit. (Adjustable devices only.) Use this button to edit the device settings for this adjustable device. The rating must be selected (i.e. non-zero) for this option to work. The Field Device Database Editor will open and the edit settings box will be shown for the selected device and rating. After adjusting the settings you may press the copy button and close the dialogues down. The paste button can then be used to paste back the settings to this circuit. (See the separate document for the Field Device Database Editor) (Adjustable devices only.) This read-only box shows the current settings for the adjustable device, or blank for the default settings. VE 2015 Field 15

16 The Cable Tab This allows you to enter further details about the cable used in this circuit. It is deliberately the same as the Cable tab in the Predefined Data dialogue box (see Predefined Data), because the items defined there may be used here if desired. Maintain link to predefined data Predefined cable details Name Description Cable type Phase If you select one of the predefined cables you may choose whether to maintain a link to it. If you do, and you subsequently re-edit the predefined cable, the changes will be reflected in this circuit and any other circuit that has maintained a link to it. If you do not, the link is broken and the data is embedded instead. If you have predefined any cables these will be available for selection here to speed up the process. This read-only box shows the name of the predefined cable selected. This read-only box shows the description of the predefined cable selected. Select a cable type. Select one of the following codes for the phase of the cable, to enable Field to check the installation method: TPN : three-phase and neutral (4-wire) TP : three-phase (3-wire) SPN : single-phase and neutral (2-wire) For single-phase we are not interested in which phase is to be used, so in this case SPN is used instead of R, Y, or B. Installation method Note that only pre-defined circuits of matching phase can be used. Select an installation method from the list. You will only be allowed to select one that is appropriate to the cable type and phase code entered in the previous items. Installation methods used in Field are based on those in Appendix 4 of BS 7671 (except VE 2015 Field 16

17 * and U). They usually comprise two parts: The first part is the installation method from BS 7671, or * when the installation method is irrelevant, or U for underground (not used at present). Minimum and maximum no. of parallel cables Minimum and maximum cable size Grouping Spacing Thermal insulation derating factor Use Equation 2 of BS7671 Appendix 4 The second part (where applicable) is one of these qualifying letters: H: horizontal, V: vertical, F: flat, T: trefoil, S: small duct, L: large duct. Limit, if required, the number of parallel cables Field is free to select on a circuit. Otherwise use 0 (no limit). Limit, if required, the size of cables Field is free to select on a circuit. Otherwise use 0 (no limit). You will only be allowed to select a size that is appropriate to the cable type, phase code and installation method entered in the previous items. Enter if known, the number of grouped circuits or multicore cables as defined in Appendix 4 of BS7671. Otherwise enter 0 and Field will calculate the maximum grouping allowed. Select the spacing between grouped cables if known. See Regulation If the cable is not embedded in thermal insulation, enter 1. Otherwise the derating factor which must be applied to this cable depends on the length of the cable embedded in thermal insulation. Select a value from Table 52A of the Regulations if the cable size is up to 10 mm², embedded less than 0.5 m in insulation of thermal conductivity greater than W/Km. For longer lengths the Regulations advise a value of 0.5. For other conditions a guidance note is given (not yet available: 18/10/91). If you enter less than 1, installation method 1F will be used automatically, as required by the Regulations (though it is open to interpretation whether this should be the case when Table 52A or the guidance note is used). The installation method you have entered will be ignored. Appendix 4 of BS 7671 gives equations for the sizing of cables with regard to currentcarrying capacity for normal and overload conditions. Field usually uses a generalised equation that is equivalent to equations (1), (2), (5) or (6), but is referred to as equation (2) for convenience. If the circuit is grouped with other circuits and they are not liable to simultaneous overload, Appendix 4 of BS 7671 allows the use of alternate equations. Field uses two generalised equations, one equivalent to equations (3) or (7), but referred to as equation (3) for convenience, and one equivalent to equations (4) or (8), but referred to as equation (4) for convenience. See Cable Sizing/Checking - Current-carrying Capacity for details of these generalised equations. Turn on or off to indicate whether equation (2) or equations (3) and (4) together should be used to calculate the required tabulated single-circuit current-carrying capacity. VE 2015 Field 17

18 The Protective Conductor Tab This allows you to enter further details about the circuit protective conductor (CPC) used in this circuit. It is deliberately the same as the Protective conductor tab in the Predefined Data dialogue box (see Predefined Data), because the items defined there may be used here if desired. Maintain link to predefined data Predefined CPC details Name Description Use armour/sheath of live cable Use core of live cable Use separate cable Use conduit Use trunking Series or parallel If you select one of the predefined CPC s you may choose whether to maintain a link to it. If you do, and you subsequently re-edit the predefined CPC, the changes will be reflected in this circuit and any other circuit that has maintained a link to it. If you do not, the link is broken and the data is embedded instead. If you have predefined any CPC s these will be available for selection here to speed up the process. This read-only box shows the name of the predefined CPC selected. This read-only box shows the description of the predefined CPC selected. Select this if you wish to use the armour or sheath of the cable carrying the live conductors. This option should not be used if there is no armour/sheath. Select this if you wish to use a spare core of the cable carrying the live conductors. This option should not be used if there is no spare core. Select this if you wish to use a separate cable. This should normally be a single-core cable. The separate cable type, length and size should be entered if this option is chosen. The size may be left blank for Field to select. The length may be left blank on final circuits only. Select this if you wish to use a metallic conduit. The length and diameter should be entered if this option is chosen. The length may be left blank on final circuits only. Select this if you wish to use trunking. The length, cross-sectional area, material and dimensions should be entered if this option is chosen. The length may be left blank on final circuits only. Select this to determine whether the elements chosen (if more than one) should be in series or parallel. Note that armour/sheath and core can only be in parallel with other VE 2015 Field 18

19 elements because they run the whole length of the cable. Note also that only 13 combinations of elements and series/parallel are available. Whenever an element is selected the unavailable combinations are disabled. The Loading Tab This allows you to select one or more predefined loads to be used on this circuit. Data should be entered on this tab for final circuits only. Select a load from the left-hand list and press Add >> to add it to the list of loads used on this circuit. Select a load in the right-hand list and use the Quantity text box or spin-button to alter the number of loads of this type to use on the circuit, or press Remove to remove it. Instead of, or in addition to, using a predefined load, you may define a provisional load for the circuit, in VA or amps. Select the units required and press the provisional load button (this is labelled with the current value). This opens the following form: VE 2015 Field 19

20 Here you may enter your load into any two of the three boxes. The other box is automatically calculated to be the correct value. The leading button may be toggled on if the phase is leading. The above example shows a load defined in amps, where the user entered 23 A for the magnitude and 0.95 for the power factor. After dismissing this box the label on the button changes as shown. The Messages Tab This displays any messages related to this circuit, and any messages for the project as a whole (not related to any circuit). Messages are (in order of decreasing severity) errors, warnings and comments, sent to alert you to problems reading the data (Import or Bridge In only), or in the calculations. Select one of the option buttons to choose which levels of severity to show. Errors may never be suppressed. The Print button prints a list of the messages, and the Add to output button adds the messages to the output file. These buttons use the same severity selection. VE 2015 Field 20

21 The Diagnostics Tab This allows you to review the diagnostic log that was produced for each circuit during calculations if the Create diagnostic log of calculations for each circuit toggle button was turned on in the Design Data dialogue box beforehand. These diagnostic logs were added to improve confidence in the Field calculations by allowing you to examine the values and equations used at each step. The problem has been that Field makes more accurate use of, for example, power factors (both in summing loads and in calculating voltage drops) and temperature corrections, than many manual calculations, giving rise to different results and occasional support calls. Now they are more easily obtained, because previously they could be requested for one circuit only and had to be stored and re-read from a file. The diagnostic log also gives an insight into the way a stage of a calculation, and all the previous stages, are repeated with larger and larger cables until the criterion for that stage is satisfied, before going on to the next stage of the calculation. Note work is still in progress to give fuller diagnostic logs, especially of the load summation and fault calculations. VE 2015 Field 21

22 The Results Tab This gives you a basic summary of the most useful results of the calculation. These may also be printed. The two other buttons show plots of voltage drops and device characteristic curves for this circuit and for all circuits upstream to the supply point. VE 2015 Field 22

23 Board When you are editing a board the Edit Board dialogue box appears. Name Number of ways Isolated Description Busbar impedance Board type Phase Display board vertically Include spare capacity and diversity Balanced Spare capacity Third harmonic (%) Diversity (%) Enter a board name. This should be unique. Enter the number of ways allowed to be taken from this board. A three-phase way counts as one way even if three single-phase circuits are taken from it. (Not used at present) Toggle this on if you wish this board and all circuits and boards downstream of it to be isolated from the source of power. Enter a description of this board. It is for information only and will appear on certain output schedules. If the type (see below) is a busbar with appreciable conductor impedances, then you need to enter here the resistances and reactances per metre of the live, neutral and earth conductors of the busbar. These are used in calculating extra contributions to voltage drop and to fault impedances for the circuits fed from various take-off points along this busbar. Select the type of board that best fits the board you wish to enter. Select the phase of this board. Toggle this on if you wish to display the board vertically. This is done for you automatically if you select a busbar type, but in any case you may override the choice. Toggle this on to specify either spare capacity, or diversity, or both, for this board. You will then need to enter data in the boxes below. (Only visible on three-phase boards) Toggle this on to enter one set of values for all three phase, or off to enter different values on each phase. Use the button to bring up a standard dialogue box to enter the spare capacity on each selected phase. Enter a third harmonic contribution expected in the spare capacity on each selected phase. Enter diversity for each selected phase. Note this applies to the total load on the board, VE 2015 Field 23

24 Include provisional loading data Provisional load Protective device type Protective device rating Make Default not just to the spare capacity. Toggle this on if you wish to add a provisional load to the board. This may be used in place of defining any circuits at the initial stages of a design. You will then need to enter data in the boxes below. Use the button to bring up a standard dialogue box to enter the provisional load. If there is a protective device that you expect to be associated with the load being defined provisionally here, select it from the list. This allows you to ensure that Field will attempt to size the device feeding this board to discriminate with the device you enter here. If a protective device was selected above, select its rating from the list. Press this button to make this board the default for any boards you subsequently add to the network. This is designed for speeding up data entry by allowing you to place a typical board, edit it to requirements, and then make it the default for any future boards. (NOTE only a pointer to this board is stored; therefore changes you make to this board after making it the default will also be made to the default Find Node Reference Use this command to find all occurrences of a particular node. The Find Node Number dialogue box appears as shown. When you enter a node number and press Find Next, the first circuit or board with that node number will be highlighted, both in the text list and in the graphics area. Further presses highlight further circuits or boards with that node number until no more are found. VE 2015 Field 24

25 Design Data Use this command to edit the design data by bringing up the design data dialogue box. Project title Enter a title for this project. This will appear on the top of each page of output. Earthing Select an earthing method. See BS7671 for details. Phase Select a phase. Nominal voltage (V) Enter the nominal supply voltage: phase-phase (line voltage) if the supply is threephase, phase-neutral otherwise. Frequency (Hz) Enter supply frequency, used to convert inductance to inductive reactance. Largest voltage drop Enter the maximum voltage drop expected at the supply to the network, as a expected at the percentage of the nominal supply voltage or in volts, depending on the units selected supply (% or V) below. % of nominal voltage Select this to show all voltage drops and voltage drop limits as a percentage of the nominal supply voltage. V Select this to show all voltage drops and voltage drop limits in volts. Enter values in the next section to help Field to calculate the short circuit and earth fault impedance of the supply, which are needed in all the short-circuit and earthfault calculations: VE 2015 Field 25

26 Supply fault level (MVA) Transformer details Both the above Short-circuit current (ka) Short-circuit impedance (% to 100 MVA base) Earth-fault impedances (ohms) Select this and enter a value if the fault level of the supply is known. Select this and enter the transformer rating (kva) and impedance (%) if these values are known. Enter the power rating of the transformer (assumed to be in a star/delta configuration) If the transformer impedance is not known a value may be entered from this table: kva Z (%) Select this and enter the values if both of the above sets of values are known. Select this and enter the short-circuit current if known. Enter the fault current (for the LV side if a transformer is used) at the supply to the network. Select this if none of the above values are known; you will need to enter some values here instead. If unsure, enter some very low values for the minima and some very high values for the maxima. For details about how to calculate these, see Calculated Supply Short-Circuit Impedances below. See Calculated DEFAULT Supply Earth-Fault Impedance below Calculated Supply Short-Circuit Impedances If you select any of the first 4 options, the data entered will be used to calculate the maximum and minimum supply short-circuit resistances and reactances. The resistance and reactance are assumed equal (i.e. phase angle = 45 ) and the minimum and maximum values are also assumed equal. If these assumptions are too inaccurate, you may calculate the values using this section as a guide and enter them directly in the 5th option. The calculations are as follows (V=Nominal Voltage from above and the 2 represents the 45 assumption): a) If Fault Level F (MVA) was entered: 10,000 for 3-phase supply, or 10,000 for single-phase supply 2 F 3 2 F b) If Transformer Rating TR (kva) and Impedance TI (%) were entered: 100,000 TI for 3-phase supply, or 100,000 TI for single-phase supply 2 TR 3 2 TR c) If Short Circuit Current SC (ka) was entered: 10,000,000 for 3-phase supply, or 10,000,000 for single-phase supply 2 3 V SC 3 2 V SC d) If a) and b) are both true, the calculated values are added together. VE 2015 Field 26

27 Calculated DEFAULT Supply Earth-Fault Impedance If you select any of the first 4 options, the data entered will be used to calculate the values of supply earth-fault resistance and reactance. The impedance is assumed to be reactive only (i.e. phase angle=90 ) so the default resistive component is zero. The default reactive component is calculated as follows (V=Nominal Voltage from above): a) If Fault Level F (MVA) was entered: V² 1,000,000 3 F b) If Transformer Rating TR (kva) and Impedance TI (%) were entered: V² TI 100,000 TR c) If Short Circuit Current SC (ka) was entered: V 3,000 SC d) If a) and b) are both true, the calculated values are added together. Protective device rating safety margins Minimum ambient temperature (deg. C) Minimum conduit size (mm) Minimum protective device rating for motor circuits (A) Motor-fuse links are required on all motor circuits Create diagnostic log of calculations for each circuit Automatically add input data to output Edit starting factors ( Sfactors ) Enter safety margins to be applied to the calculated minimum device rating for each of the categories. The value must not be less than 1 to satisfy BS 7671 Regulation (i). Enter the minimum ambient temperature. This is used in calculating maximum fault currents in the network. Enter a value for the minimum conduit size. This is the minimum diameter for any conduit used within the installation. A typical value is 16 mm. Select a diameter from the values 16, 20, 25 and 32. Enter the minimum device rating for circuits feeding cage-type induction motors. This is used in selecting motor-circuit protective-devices. If toggled on, Field will select motor-circuit fuse-links on all motor circuits. The choice for any particular circuit may be overridden if required. If toggled on, any subsequent calculation will produce a full diagnostic log for each circuit, which can be examined by editing the circuit. If toggled on, a record of all the input data will automatically be added to the output file just before calculations are requested. Press this button to edit s-factors see below. VE 2015 Field 27

28 s (starting)-factors are used to ensure that the device rating does not trip during the starting period (see Protective device data s-factors). Enter s-factor values for the various load types and for numbers of occurrences of these load types from 1 to 6. Note that s-factors should decrease with increasing number of occurrences. For each number of occurrences of each load type, Field obtains the minimum device rating for the inrush current by multiplying the total normal running current of all the loads of this type by the relevant s-factor. For mixed load types the sum of the individual contributions is used. The s-factors must then be deduced by working back from data provided by the load or device manufacturers, showing either recommended ratings or starting- current envelopes for various numbers of occurrences of the loads. At best this is a compromise between the different load and device types and manufacturers. Default values are provided when new projects are started, as below: Default s-factors Number of occurrences of load type Load type Lamp Type I Lamp Type F Lamp Type SOX Lamp Type SON Lamp Type MBF Lamp Type MBT Lamp Type MBI Heaters Cookers Control Panels VE 2015 Field 28

29 Predefined Data Use this command to Edit the predefined data for this project. You may use predefined data to speed up data entry. Up to 100 sets of predefined data, in three categories, may be set up and stored with a name and description for each. The categories are: Predefined circuit details Predefined cable details Predefined circuit protective conductor (CPC) details A predefined data set from each category may then be used on any circuit, in one of two ways: As a copy, so that further changes may be made on the copy if desired As a link, so that further changes are not allowed but that any changes to the predefined data will show up in all the circuits using it The Predefined Data dialogue box uses exactly the same tabs as those on the Edit Circuit dialogue box, to make it easier to learn Field. However, there are some small differences: Predefined Data dialogue box (defining) No Maintain link toggle buttons not needed when defining. Name and Description edit boxes are enabled needed when defining. Add, Delete and Edit buttons to enable user to define. Edit Circuit dialogue box (referencing) Maintain link toggle buttons needed to decide whether to reference a copy or a link to the predefined data. Name and Description edit boxes are disabled not needed when referencing. No Add, Delete and Edit buttons not needed when referencing predefined data. The tabs are shown below. For details of how to enter data, refer to the Edit Circuit dialogue box. VE 2015 Field 29

30 Predefined Circuit Data Tab Predefined Cable Data Tab VE 2015 Field 30

31 Predefined CPC Data Tab Loads Data This command brings up the Loads dialogue box. You may use this to define loads, each of which may be used later on as many circuits as you wish. Loads are optional because you may decide to use provisional loading data only at an early stage of a design. At a later stage you may wish to enter more specific loading details here and use them on circuits. Loads are divided into eight categories. The Loads data dialogue has eight tabs, one for each category. These are described in the following sections. However, some of the items are common to all (or nearly all) of the tabs and are described below. Name Description Number of stored records: <n> Current record= Add Change Remove Enter a name for this load, up to 4 characters. This name must be unique to this load, i.e. no other load of any type must have the same name. This combo box may also be used for moving between loads for review or edit. As you do this the Current record= item below and all the other items will also change to reflect the load chosen. Enter a description for this load. This will appear on certain output schedules. This shows you how many loads of this type have been defined (where <n> is replaced by the actual number). This text box or spin button can be used to move from one load to another to review or edit. As you do this the Name item above and all the other items will also change to reflect the load chosen. Use this button, after making changes to the current load in the dialogue box, to add it as a new load at the end of the list of loads. You will prevented from adding a new load until you give it a new name. Use this button, after making changes to the current load in the dialogue box, to save it back to the same place in the list of loads. Use this button to remove the current load from the list of loads. VE 2015 Field 31

32 Lighting Loads Tab Available luminaires Quantity Split Phase Edit Luminaires Add Remove Luminaires used in this lighting group Select a previously defined luminaire to be used in this lighting group. Enter the number of luminaires of this type to use in this lighting group. If this luminaire is to be used in a three-phase lighting group, select which phase it is to be used on. Otherwise set Split Phase to No. Displays a dialogue box (see Luminaires dialogue box) that allows you to edit the luminaires used in the project. Adds the currently-selected luminaire, quantity and phase to the list of luminaires used in this lighting group. Removes the currently-selected luminaire, quantity and phase from the list of luminaires used in this lighting group. Shows the luminaires used in this lighting group, with their quantities and phases. Note you may use a particular luminaire on more than one phase of a split-phase lighting group. VE 2015 Field 32

33 Luminaires Dialogue Box Name Lamp type Loading Number of lamps Lamp rating (W) Third harmonic (%) Device type Device rating (A) This name may be the same as a lighting group name if you wish, but it must be unique within the list of luminaires. Select the type of lamp from the list. Press this button to edit the loading data. Enter the number of lamps in this luminaire. This is used when finding the s-factor for the selection of device rating to accommodate inrush current. Enter the output rating of the lamp. This will appear in luminaire schedules. Enter the third harmonic as a percentage of the total circuit current of the luminaire. Field will take these into account when calculating the out-of-balance currents in neutral conductors. Select a device if one is incorporated in the luminaire. Field will take account of this in discrimination calculations. Select the rating of the device. VE 2015 Field 33

34 Motor Loads Tab Status Phases Poles Starting method Starting current (A) Starting duration (s) Output rating (kw) Efficiency (%) Power factor Full load current (A) Select Duty or Standby. Standby motors will be excluded from the load summation, but the device and cable will still be sized. Select 1 or 3 phases. Select the number of poles. When standard motor data is used, this enables Field to find the relevant standard data. Select one of the starting methods. If non-standard is selected, you must enter the starting current and duration below. If star-delta with non-localised starter is selected, Field will calculate the size of the cable assuming that there are six cables to the motor, instead of three. If the starting method is non-standard, enter the starting current. Field will compare the point given by the maximum starting current and duration to the characteristics for the relevant device type and select the lowest rating whose characteristic passes above the point. If the starting method is non-standard, enter the starting duration. If standard motor data is used, but a non-standard rating is entered, Field will adjust the motor characteristics by interpolation or extrapolation. Enter the motor efficiency. If standard motor data (see Motor Data) is not required, enter data in 2 items out of this one and the next two (power factor and full-load current). Press the? button to calculate it from the other values. Enter the power factor. Press the? button to calculate it from the other values. The calculated value is: Output Rating (Efficiency x No. of Phases x Full-Load Current x Phase Voltage). Enter the full-load current of the motor. Press the? button to calculate it from the other values. The calculated value is: VE 2015 Field 34

35 Set these 3 items using standard motor data Overcurrent trip (%) Fused connection unit? Protective device type Protective device rating Output Rating (Efficiency x No. of Phases x Power Factor x Phase Voltage). This button will use standard motor data to fill in suggested values for the three items above, based on the number of phases, the number of poles, and the output rating. If a value is entered, Field will base the current-carrying capacity of the final circuit cable on I = trip/100 x full-load current of the motor. If no over-current trip is required, enter 0. Select Yes if the load is single-phase and connected by FCU, No otherwise. Field will indicate on output schedules where equipment is connected by FCU. For standard circuits (A1, A2 or A3) Field will assume connection by FCU. If there is a protective device incorporated into the load being defined here, select it from the list. If a protective device was selected above, select its rating from the list Heater Loads Tab Load (kw) Enter a load in kw. The power factor is assumed to be 1. Phases Select 1 or 3 phases. Fused Select Yes if the load is single-phase and connected by FCU, No otherwise. Field will connection unit? indicate on output schedules where equipment is connected by FCU. For standard circuits (A1, A2 or A3) Field will assume connection by FCU. VE 2015 Field 35

36 Cooker Loads Tab Load (kw) Enter a load in kw. The power factor is assumed to be 1. Phases Select 1 or 3 phases. Socket outlet present? Select Yes if the load is a single-phase cooking appliance with a socket outlet included, No otherwise. This is used in calculating diversity as in Appendix 4 of the IEE Regulations (15th. Edition).. Diversity If the above is toggled off, enter the diversity of the cooking appliance. The design load will be calculated as this percentage of the connected load. Use default diversity Toggle on if you wish Field to use the diversity from table 4A of the IEE from regulations? Regulations (15th. Edition) for Household cooking appliances. The design load will be calculated as this percentage of the connected load. VE 2015 Field 36

37 Socket Loads Tab Socket type Rating (A) Number of singles Number of twins Phases Loading Select one of the following socket types: BS A (1-phase only, single or twin outlets) BS546 2, 5, 15, 30A (1-phase only, single outlets only) BS196 5, 15, 30A (1-phase only, single outlets only) BS A (1-phase only, single outlets only) BS , 32, 63, 125A (1 or 3-phase, single outlets only) US-STYLE 15, 20A (1-phase only, single or twin outlets, 110V) Enter a rating. This must be one of the allowed ratings for the socket type. Enter the number of single socket outlets in this socket group. These are used in calculating the aggregate rating of the socket group. Enter the number of twin socket outlets in this socket group. These are used in calculating the aggregate rating of the socket group. Note that some socket types are available as single outlets only. Select 1 or 3 phases. Use this button to enter a total loading for the group of sockets. Field will use this to calculate the connected load for the circuit on which this socket load is used. The same value will be added into the connected load and the design load for the distribution equipment. However, the design load for the circuit itself will be calculated as in Load summation design load on final circuits, for the reasons given there. VE 2015 Field 37

38 Control Panel Tab Set Load (kw) Phases Diversity Third harmonic (%) Starting current (A) Starting duration (s) Overall voltage drop limit (% or V) State Fused connection unit? Protective device type Protective device rating Use this button to set the load kw, kva and power factor. Select 1 or 3 phases. Enter the diversity. The design load will be calculated as this percentage of the connected load. Enter the third harmonic as a percentage of the total circuit current of the load. Field will take account of third harmonics when calculating out-of-balance currents in the neutral conductor. Not required for control panels. Not required for control panels. See Regulation Enter the overall voltage-drop limit (including the voltage drop at the supply) to be imposed on the circuit feeding this control panel. This will be in % of the supply voltage, or in volts, depending on what you chose in the Design Data dialogue box (see Design Data). The warning limits are between the supply voltage drop +0.1 percent and +4.0 percent, and the error limits are between the supply voltage drop plus 0.1 percent and 20 percent. Select Duty or Standby. Standby loads will be excluded from the load summation, but the device and cable will still be sized. Select Yes if the load is single-phase and connected by FCU, No otherwise. Field will indicate on output schedules where equipment is connected by FCU. For standard circuits (A1, A2 or A3) Field will assume connection by FCU. If there is a protective device incorporated into the load being defined here, select it from the list. If a protective device was selected above, select its rating from the list. VE 2015 Field 38

39 Elevators Tab See Control Panel tab. The only differences here are that the starting current and duration may be entered and that the Diversity must be 100%: Diversity Starting current (A) Starting duration (s) Diversity must be 100% for elevators. The design load will be calculated as this percentage of the connected load. Enter the maximum starting current and duration if you want Field to size the protective device for the starting current. Field will compare the point given by the maximum starting current and duration to the characteristics for the relevant device type and select the lowest rating whose characteristic passes above the point. Enter the starting duration (see above). VE 2015 Field 39

40 Others Tab See Control Panel tab. The only differences here are that the starting current and duration may be entered. Starting current (A) Starting duration (s) Enter the maximum starting current and duration if you want Field to size the protective device for the starting current. Field will compare the point given by the maximum starting current and duration to the characteristics for the relevant device type and select the lowest rating whose characteristic passes above the point. Enter the starting duration (see above). VE 2015 Field 40

41 2.3. View Menu Note the view menu is also available using the right mouse button in the graphics area Zoom In Use this command to expand a part of the graphics window to fill the whole window. When you select the command the prompt in the status bar changes as below. VE 2015 Field 41

42 Move the mouse pointer to one corner of the area you wish to expand (the zoom rectangle). Press the button and hold it down while you move the mouse pointer. This will start dragging the other corner of the zoom rectangle as shown below. When you release the mouse button the zoom rectangle is expanded to fit into the view as shown below. Note that even though the zoom rectangle may be a different shape from your window, the zoom will be performed in such a way that the entire rectangle will still be visible. VE 2015 Field 42

43 Zoom Out Use this command to zoom out so that approximately twice the area is now visible in your graphics window Zoom All Use this command to zoom to fit the entire network into your graphics window Refresh Use this command to redraw the network in your graphics window in case any of the dragging, etc. has left traces on the screen Axis Lock Use this command to restrict node drags and circuit placement so that your second mouse click is restricted to have either the same x-coordinate or the same y- coordinate as your first mouse click, i.e. it locks movement to either the x or y coordinate axis. This is useful in certain circumstances. VE 2015 Field 43

44 Export DXF Use this command to export the entire network graphic in DXF format. This command does not depend on the current view zoom. A Windows standard Save File dialogue box will open asking you for the file name. When you press Save you will be asked whether you wish to export the layer table, and then the file will be created Print Drawing This is identical to the same option on the File menu (see Print Drawing) Grid Use this command to turn on or off a grid in the graphics window. When the grid is on any placement or drag will be restricted to grid points. This may be used to tidy up alignments of circuits, boards, etc. Note that the grid is only visible at high enough zoom magnification. VE 2015 Field 44

45 Font Scale Use this command to adjust the size of the text in the graphics window. The factor you enter is relative to the standard value (=1). Note this affects the text size on printouts as well as in the graphics window Dynamic Scroll This affects how scrolling occurs. When it is off, the graphic area is not redrawn until you stop dragging the thumb on the scroll-bar, making it harder to scroll precisely. When it is on, you can see the graphic area being redrawn dynamically while the thumb is being dragged. Because this makes scrolling slightly slower, only outlines are shown during dynamic scrolling Quick Draw When this is on, only outlines will be drawn, for increased speed Fence Overlap When this is on, any elements intersecting the selection fence are also included in the selection. VE 2015 Field 45

46 2.4. Database Menu Devices Use this command to edit and review protective devices from the database. This runs the device database editor Fielddb.exe, which may also be run standalone, i.e. directly from Windows, if you wish. See the separate document Field Device Database Editor User Guide for details Cables Use this command to edit and review cables from the database. The Cable database dialogue box opens, allowing you to select a cable from a list box. VE 2015 Field 46

47 This has several buttons: Import - this allows you to import new cables from text files. Not available yet Export - this allows you to export selected cables to text files. Not available yet. Copy - this allows you to copy a cable from another Field database. Not available yet. Add - this allows you to add and edit a new cable. The Field cable database editor will open. See Edit. Review - this allows you to see the data for the selected cable. The Review dialogue box opens to show you the relevant data. Edit - this allows you to edit the selected cable. The Field cable database editor will open. VE 2015 Field 47

48 Delete - this allows you to delete the selected cable. Close - this closes the Cable database dialogue box Database Path The custom database path is the location of the system database on your system. This is where system-wide data is available for Field to use, comprising devices, cables, and customised output schedule formats. If the DOS environment variable Field has been set, then the initial custom database path is set to that path, for all Field projects. Otherwise the initial custom database path is blank, for all Field projects. If the custom database path is blank, then Field uses the system database from the Field folder below where Field.exe is installed. Otherwise, Field uses the database from this path. Note wherever the system database is located; any user changes to the database are always stored in the local database, not the system database. The local database is in the Field folder below the project. Use this command to set or change the custom database path for the current project only. The Custom Database Path dialogue box opens, with a box showing the current path (if any): VE 2015 Field 48

49 To clear the current path (if any) select it and press Remove. Press Browse to browse around your system for a folder where a Field database can be found. This opens a Windows standard Browse for Folder dialogue box (shown below). Press OK when the path is correctly set or cleared, or Cancel to revert to the previous setting. If you press OK the new path will then be saved with the project. To set or change the custom database path for all projects that do not have their own path already set; you must use the Field DOS environment variable. The easiest way to do this is to put a line set Field =<required path> in the file autoexec.bat. VE 2015 Field 49

50 2.5. Calculations Menu The Calculations menu allows you to select which calculation you wish to perform Network Calculations Selecting this command allows you to run the standard network calculations. First of all, a question appears: Answer Yes if you want to start afresh with an empty output file, or No to keep what is already in the output file, maybe from a previous calculation. If you have selected automatically add input data to output on the Design Data dialogue box then a summary of the input data will be added to the output file at this point. The calculations will then proceed, unless there are errors preventing this. The calculations include the following (see Calculation methods for more details): Load summation (connected load and design load), including neutral-current and third-harmonic contribution. Sizing/checking of device ratings for design load, for starting or inrush current and for discrimination against other devices. Sizing/checking of cables for design load, for voltage drop and for shortcircuit and earth-fault energy withstand and disconnection time. Sizing/checking of CPC's for similar design constraints. Incidental results obtained also include maximum groupings, short-circuit and earthfault currents, impedances, energy let-throughs and disconnection times, and circuit and overall voltage drops. The number and type of calculations performed by Field will depend on the data you enter and the results you require. In particular the device, cable and CPC sizing will only be performed if you have not set the sizes on input. If you have, the sizes you have set will be checked instead. VE 2015 Field 50

51 When the calculations are complete, you will be given a count of errors, warnings and comments. You may review these messages using the Review Messages option (see Messages) Single-Circuit Calculation Selecting this command allows you to perform a single-circuit calculation on the selected circuit only. Not available at present CostPlan Output Selecting this command allows you to produce output to file that can be used as input to CostPlan. The file will automatically be named the same as the project file but with a *.cst extension. CostPlan will then need to be run separately using this file as input. VE 2015 Field 51

52 2.6. Review Menu The Review menu includes commands that let you review input data, messages, and various types of results. All review options that come to screen may also be printed or added to the output file. Most of them appear in a resizable Review dialogue box, the contents of which may be scrolled, selected, copied, added to output or printed Input Data This option brings up a sub-menu of the different types of input data: The Review Input Data menu consists of: Design Data Predefined Data Load Data Network Data Use these options to review the data required. Each set of data is shown in a Review dialogue box. VE 2015 Field 52

53 Messages This option displays the Messages dialogue box. This contains a Messages tab (see below), very similar to the one used in the Edit Circuit dialogue box (see The Messages Tab). The only differences are: The top pane lists messages for circuits in general rather than for the one particular circuit being edited. When one or more of these messages are highlighted the appropriate circuits are also highlighted in the text list and the graphics area on the main window. This can be useful to help you to identify the parts of a network having a particular type of problem. So, for example, to see all the circuits which have errors, select Show errors only, and then highlight all the error messages; or, to see all circuits with voltage drop problems, highlight the appropriate messages it may give you a clue as to the cause, because all the circuits may be fed from a particular board. VE 2015 Field 53

54 Equipment Load Balance This option produces a drawing of all the boards selected, or the 8 most unbalanced boards, showing a little histogram of loads split by phase, so that you can visualise the balance between phases General Load Summary This option displays a general load summary in a Review dialogue box. This is a summation of all loads on a board-by-board basis. VE 2015 Field 54

55 Fixed Schedules This option displays the Fixed Output Schedules dialogue box. At present two fixed schedule formats are available, Basic Schedule and Detailed Schedule. They are suitable for reviewing most of the fundamental data on a board-by-board basis. Select all the boards for which you wish to have schedules in the left-hand pane. Use Select All or Clear All to speed up the process. Select the required schedule in the right-hand pane. Then press Create Schedules to create all the requested schedules. These appear in a Review dialogue box. VE 2015 Field 55

56 Customised Schedules This option displays the Customised Output Schedules dialogue box. There are several customised output schedule formats (although some of these are examples not meant to be used in real situations) and it is possible for you to create and edit your own in addition. Select all the boards for which you wish to have schedules in the left-hand pane. Use Select All or Clear All to speed up the process. Select the required schedule in the right-hand pane. Then press Create Schedules to create all the requested schedules. These appear in a Review dialogue box. Press Edit Schedules if you wish to edit the formats (templates) for customised output schedules. The Field Customised Output Schedules dialogue box will open. VE 2015 Field 56

57 Selecting a schedule and pressing Add will add a new schedule based on the selected schedule, and bring up the edit box for this new schedule. Selecting a schedule and pressing Edit will bring up the edit box for the currently-selected schedule. In either case the Edit Customised Schedule dialogue box will appear. VE 2015 Field 57

58 The top tabs represent different types of circuit data (input and results) that are available for use in your schedule format. The bottom tabs represent the items of data already in use, arranged according to section. Two sections represent the main table (Part 1) and a continuation table (Part 2), and four sections represent total lines which show data from the circuit feeding the board in question. The arrows allow the order of data in any section to be modified. Follow the instructions on screen for modifying the layout of your customised schedule by selecting items from the top tabs for inclusion in any of the bottom tabs, or by removing or changing the order of items in the bottom tabs. At any stage the View button may be used to examine the effects of the changes you are making. This is the fastest way to learn what the different sections mean, because the View Schedule dialogue box shows them laid out as in the finished schedule. VE 2015 Field 58

59 Key to Schedules This option displays the key to symbols used in the schedules in a Review dialogue box. VE 2015 Field 59

60 Equipment Analysis This option displays a breakdown of load demand by load type Load Schedule This option displays a summary of loads of each type, with the quantity used. VE 2015 Field 60

61 Distribution Equipment Schedule This option displays a summary of all the distribution equipment, showing the largest device and the maximum short circuit current Device Schedule This option displays the schedule of devices and quantities by rating and number of phases. VE 2015 Field 61

62 Cable Schedule This option displays a schedule of cables, quantities and total lengths by size and number of cores Abbreviations and Codes This option displays the abbreviations and codes used in Field, in a Review dialogue box. VE 2015 Field 62

63 Output File This option displays the output file. This uses a different type of dialogue box which allows you to print the output file and/or save it. If it is not saved, it will be lost at the end of a Field session Help Menu Contents This option displays the help file for Field. Note pressing F1 at any stage will bring up this help file, on a suitable page according to where the cursor was when F1 was pressed Help on Help This option displays the standard Windows Help on Help help file, telling you more about how to use the Windows Help system. VE 2015 Field 63

64 About This option displays the About dialogue box. The caption of this box is the quickest and most reliable way to find out what version of Field you are running (the splash screen also shows this). Please find out the version number before you make a support call. VE 2015 Field 64

65 3. Tool Buttons The tool buttons save you time by enabling you to select some of the most frequently used commands, without having to select them from the pull down menus at the top of the Field window Main Toolbar The main toolbar is described below from left to right. New Project (see File menu) Open Project (see File menu) Save Project (see File menu) Bridge In (see File menu) Import V.10, V.11 Project (see File menu) Add circuit (see Edit menu) Add board (see Edit menu) Edit (see Edit menu) Delete (see Edit menu) Network calculations (see Calculations menu) Messages (see Review menu) Print output (see File menu) Find node reference (see Edit menu) Help contents (see Help menu) 3.2. Status Bar The status bar is used for displaying messages about the status of activities in Field and for displaying prompts, especially during graphical manipulations in the Graphics screen. It is highly recommended that you keep an eye on this for important prompts when you are performing graphical manipulations such as adding circuits or boards, zooming in, putting a selection fence around items, dragging and copying selections, etc. VE 2015 Field 65

66 4. Selection of Boards and Circuits Various activities in Field require you to select one or more branches (boards or circuits), for editing, deleting, etc. or to select a node (a connection point on boards and circuits), for dragging. The text list (like any standard extended-selection list box in Windows) allows you to: Select individual branches by clicking the mouse on the list. Select consecutive branches by dragging the mouse over the list. Add or remove individual branches to or from the selection set by pressing Ctrl and clicking the mouse on the list. Add or remove consecutive branches to or from the selection set by pressing Ctrl and dragging the mouse over the list. The graphics window, in its default state, expects you to do one of the following: Select a node to drag. Select a branch (board or circuit) to drag, copy or edit. Add or remove a branch from a selection set. Start dragging a fence rectangle to select one or more branches. Start dragging a fence rectangle to add one or more branches to a selection set. VE 2015 Field 66

67 To select a node to drag, simply move the mouse pointer near to a node at one or other end of a circuit, and the pointer will snap to the node point. If you press the mouse button and drag it, the node will be dragged. If the circuit is connected to a board at that node, you will be asked whether you wish to disconnect it. If you do not, the drag will be stopped. To select a branch to drag, copy or edit, simply move the mouse pointer to a part of the circuit or board not too close to the nodes. Click the mouse button and the circuit will become highlighted. To drag the selected branch, press the mouse button again and this time keep it down while you move the pointer. After the drag is finished, any connected ends will be readjusted so they are still connected. The middle section of a circuit may be dragged without moving the ends. To copy the selected branch, hold down the Ctrl key while dragging. The original branch will be left where it was and a copy will be dragged instead. To edit the selected branch, double-click it with the mouse or select the Edit menu option or toolbar button. To add or remove a branch from a selection set, hold down the Ctrl key while you select it VE 2015 Field 67

68 To start dragging a fence rectangle to select one or more branches, press the mouse button when the pointer is over a space where there are no branches and drag it while holding it down. In this example the mouse pointer is dragged from the top left of the window: As you drag the pointer, you will be dragging a rectangular fence. If View > Fence Overlap is turned on, keep dragging the fence until it encloses or intersects all the branches you wish to select. If View > Fence Overlap is turned off, the dragged fence must enclose all the branches you wish to select. In this example, View > Fence Overlap is turned off and the fence is being dragged to select nearly all the boards and branches: VE 2015 Field 68

69 When you have finished dragging the fence, release the mouse button. The enclosed branches will all be selected and highlighted, as shown below for our example: VE 2015 Field 69

70 Note that the intersected circuits were selected because View > Fence Overlap was turned on. You may now edit (only if there is only one item selected), or drag to move or copy the selected items as for a single selection. In this example the selection is being dragged to move the selected items: VE 2015 Field 70

71 To start dragging a fence rectangle to add one or more branches to a selection set, simply hold down the control key while the fence is being dragged. Unlike individual selection with the Ctrl key held down, this cannot be used to remove branches from the selection, only to add them. VE 2015 Field 71

72 5. Program Size Limits Field allows up to 3000 circuits, 500 items of distribution equipment, 1000 loads and 3000 connections of loads to circuits. Up to 10 cable types and 42 protective-device types (with 224 individual ratings) can be held in memory simultaneously; more can be treated but this incurs a speed penalty as data is paged from disk. VE 2015 Field 72

73 6. Voltage Drops Various percentage voltage drops or voltage drop limits are required in the input data. This diagram may help to clarify which voltage drops are being set or limited in the various dialogue boxes: VE 2015 Field 73

74 7. Customised Schedules The Review menu has a facility for obtaining customised schedules of distribution equipment. All the information required is held in two standard datafiles: citems1.dat contains a complete list of all the items of data available for customising your own schedule formats. The items of data are grouped into types, and within each group the individual items are given a number. For each item of data, information is stored about the format, scale factors, units and headers to be used if it is included in a customised schedule. Note this file is strictly formatted and should not be edited. cforms1.dat contains prepared formats for each customised schedule. For each schedule, the title is stored, followed by pairs of data types and numbers to specify each item to be included in the schedule. See Customised schedule data for more information. You may modify, add or delete customised schedule formats in cforms1.dat. This may be done directly using any text editor with which you are familiar, but the preferred method is to use the editing facility provided, which actually creates an edited copy of cforms1.dat in the Field folder below your project, so that the installed customised schedule formats are not lost. Here are two examples of formats for customised schedules from this file. You can see other examples by examining the file, and you can compare some of them with the resultant output schedules for the example run): Design Data , 1, 1, 2, 1, 1, 1, 2, 2, 2, 2, 8, 8, 8, 8, 2, 2, 2, 2, 2, 2, 8, 2, 8, 2 3, 33, 12, 91, 16, 34,35, 2, 38, 6, 8, 5, 1, 2, 3, 7, 3, 70, 71, 73, 72, 11, 85, 6, 41 Maximum Fault Level (ka) is 2 52 Maximum Upstream Earth Loop Impedance (ohm) 2 65 Total Upstream Voltage Drop (%) is 2 42 is VE 2015 Field 74

75 Example Schedule: , 1, 1, 2, 2, 2, 3, 3, 3, 2, 2, 2, 5, 5, 5, 5 1, 2, 3, 1, 2, 3, 1, 2, 3, 1, 2, 3, 1, 2, 3, 4 Note that the formats are simply placed one after the other in the file, and include the three standard schedules (load analysis, design data and installation data). The second example is simpler so we shall examine this first: Line 1 contains the required title, Example Schedule. Line 2 has 6 numbers indicating how many items required, respectively, in: Part 1, a table repeated for each circuit on the equipment. Part 2, a continuation table below Part 1 if there are too many items for one table because of the limited width of the output paper. Total 1, the first of four summary lines for the whole equipment. Total 2, the second '' '' '' '' '' '' '' '' Total 3, the third '' '' '' '' '' '' '' '' Total 4, the last '' '' '' '' '' '' '' '' In this case, the schedule requires 16 items to be tabulated for each circuit (Part 1), but no continuation table (Part 2) or summary lines (Totals 1 to 4). The items in Part 1 are to be tabulated under a header which is automatically generated from the data held in file citems1.dat. Lines 3 & 4 contain pairs of data types and numbers for each item required in Part 1 - the data types on line 3 and the numbers below each data type on line 4. E.g. the 6th item in Part 1 is data type 2, CIRCUIT RESULTS, item number 3, Maximum Grouping. (If a Part 2 had also been required, the pairs of data types and numbers would have followed on from the similar lines for Part 1, and the header would be generated in a similar way.) The Design Data schedule is slightly more complicated, having 26 items in Part 1, still no continuation table (Part 2), and 3 summary lines (Totals 1 to 3) with 1 item each. Totals 1 to 4, being summary lines, are not given a header in the same way as Parts 1 or 2, so they need an extra line detailing the text which is required to precede the items on the line of output. If the text includes character it will be replaced by the current board description. The items for Totals 1 to 4 follow this text line. VE 2015 Field 75

76 8. Calculation Methods 8.1. Load Summation General This is done vectorially using input values of W, VA and power factor. For threephase circuits each phase is summed separately, though for convenience balanced loads are input and output as single values. The third harmonic is summed separately and carried forward for calculation of neutral current Connected Load The input values of connected load are summed, without spare capacity or diversity, throughout the installation. Power factor is taken into account. Totals, expressed as kva, are output for each final circuit, for each board, and for the complete installation. Secondary summations provide totals of connected load (kva) under load type headings. Quantities of each type of equipment subdivided into type and rating are also summed. These are output by the Schedules of loads option on the output menu. Any load designated standby is not summed, but is carried to the secondary listings of loads and shown as standby. Note that the presence of at least one item of standby equipment amongst the loads on a circuit effectively makes the whole circuit standby Design Load on Final Circuits The design load is used to select a device rating and cable size for a circuit. Where more than one type of load is connected to a circuit, the contribution from each load is added into the total design load. The contribution depends on the load type as explained below. It is equal to the connected load for lighting, motors, heating, lifts and control panels, but standby equipment is not summed. The standby design load is however used in selecting the device for the circuit and sizing the cable. For cooking appliances, diversity is applied either in accordance with Table 4A of the IEE Regulations (15th. Edition) or as a percentage of connected load, as directed by the input in the cooking appliance data. VE 2015 Field 76

77 For non-classified loads, diversity is applied as a percentage as entered in the relevant data. However, the diversity of elevators must be entered as 100 percent. For socket circuits, special considerations apply as explained below. Field is using the old Appendix 5 (now removed) of the 15th. Edition of the IEE Regulations and of BS The old Appendix 5 says that any of the socket circuits dealt with (except cooker circuits), and not just the standard A1, A2 or A3 circuits, must have a corrected current-carrying capacity, Iz, not less than In, the device rating (multiplied by 2/3 if it is a ring circuit). This appears to mean that the design current, IB, must be set equal to In if the old Appendix 9 (now 4) is to be used, as required when the circuit is grouped. Otherwise the use of the alternative equations in the old Appendix 9 (for groups in which the circuits are not liable to simultaneous overload) would result in Iz being less than In. When IB is set equal to In, no matter which old Appendix 9 equation is used, Iz will not be less than In. In a nutshell, the old Appendix 5 forced IB to be set equal to In. This is probably because there is no way to ensure that a socket circuit may not be loaded right up to the limit imposed by the device rating and seems sensible in normal circumstances. However, it was only advisory (see old Appendix 5 and old Regulation 314-3, now ). A circuit could satisfy the old without complying with the old Appendix 5 as long as it satisfied Chapters 43, 46 and 52, and in particular the old (now ). Although the old also said that Iz must not be less than In, it referred to the old Appendix 9 where the use of the alternative equations when the circuit is grouped may result in Iz being less than In, as long as IB can be safely assumed to be less than In. Also, voltage drop depends on IB, and results in larger cables than really necessary if IB is set equal to In but is unlikely to be as high as In practice. Unless you specify otherwise, IB is established as follows: Standard socket circuits (A1 ( ); A2, A3 (Appendix 5, 15th. Ed.)): IB = In Other socket outlets - depends on the mix of loads on the circuit: 2A sockets: IB = connected load, subject to minimum 0.5A per socket Other ratings, one socket only: IB = socket rating Other ratings, more than one socket: IB must be set by user Other ratings, non-socket loads included as well: IB must be set by user To get a realistic cable size for voltage-drop considerations simply enter a realistic value of IB for Fix IB for Voltage-Drop Calculations on the input data for the circuit. This will not affect the value of IB used in the current-carrying capacity calculations. If IB must be set, or if you want to set it anyway since the circuit is grouped with other circuits not liable to simultaneous overload and IB can be safely assumed to be less than In, enter a realistic value of IB for Fix IB for Voltage-Drop Calculations as VE 2015 Field 77

78 above, but also enter Yes for Fix IB Also for Grouping. Also you must ensure that the predefined circuit being used has No for Use Equation 2 of Appendix 4. The aggregate rating of all sockets on a circuit is calculated and included on output to assist the user to determine design load, but the aggregate is not summed beyond the final circuit. The contribution to the design load of the upstream distribution circuit is determined differently when socket circuits are involved - see Load summation design load on distribution circuits Design Load on Distribution Circuits At each board the sum of the design loads of outgoing circuits, plus spare capacity where appropriate, is multiplied by the diversity. The values are output in kva and power factor for each distribution circuit and for the complete installation. However, when one of the outgoing circuits is a final socket circuit, the contribution of the sockets to the design load of this circuit (see Load summation design load on final circuits) is not included in the summation. This is because this is normally set equal to the device rating (multiplied by 2/3 for a ring circuit) to ensure that the cable is protected no matter what load is drawn from the sockets, but this would be an unrealistically high load to carry up to the distribution equipment. Instead, the socket loading as given in the socket data is included, assuming that it includes an allowance for diversity Design Current This is calculated from the design VA divided by the nominal voltage of the supply. When the supply is three-phase, the line voltage is used throughout, with the factor 3 applied to single-phase circuits: so for a 400V supply the single-phase voltage is taken as V and current values are slightly different from those calculated at 230V. For single-phase supplies the input phase/neutral voltage is used throughout. For distribution circuits the design current is derived from the design load. In the case of TPN circuits with unbalanced load, the highest phase current is used for all subsequent calculations Neutral Current For TPN circuits with unbalanced load, this is derived as follows: Any third harmonic component is subtracted from each phase. The fundamental currents are resolved vectorially, allowing for power factor. The third harmonic currents are resolved vectorially, allowing for power factor. The resultant VE 2015 Field 78

79 fundamental and third harmonic currents are summed arithmetically and the third harmonic component expressed as a percentage of the total. VE 2015 Field 79

80 8.2. Device Selection/Checking Basic Factors The type of device must be selected. However, the rating does not have to be entered. If it is not entered, Field selects it; otherwise, Field checks it. To select or check the device rating, the following criteria are used: Circuit design current Starting or inrush current (final circuits only) Discrimination with each downstream device under overload conditions. The selected rating will satisfy as many as possible of these criteria. A warning or error will be given if it is not possible to select a rating to satisfy all the criteria, or if there is inadequate data to select a rating. Later, when the cable sizing calculations are carried out, further checks are made that the device will also discriminate with each downstream device under fault conditions, and have a sufficiently high breaking capacity for the fault current or are protected by the upstream device. See the later sections on short-circuit and earthfault calculations Design Current Field attempts to satisfy BS 7671 regulation (i) so that the nominal current or setting of the device is not less than the design current of the circuit. The rating margin in the Design Data is used so that the nominal current or setting of the device is not less than the product of design current and rating margin Starting Current For a circuit with one cage induction motor and GEC BS88 fuse, selection will be in accordance with the Tables in Protective device data device selection on motor circuits when a standard starting condition has been input. For a circuit with one cage induction motor, GEC BS88 fuse and non-standard starting data, Field does not attempt to ensure that the rating it selects will cope with starting current. In a future version of Field, reference will be made to the pre-arcing time/current characteristics of the fuses. The selected rating will be that whose characteristic passes through or above the coordinate given by the motor maximum starting current/duration. For all other cases the user must set the rating. VE 2015 Field 80

81 Inrush Current You may input s-factors for an analysis or use your firm's default data. See Protective device data s-factors for details of how to modify the default data. Lighting is used here as an example of the application of s-factors, but the principle also applies to heaters, cookers and control panels. The total number of each type of lamp is determined. The total current demand of each group of a lamp type and associated control equipment is multiplied by the appropriate s-factor. The selected rating must be greater than the sum of the resultant values. This can be represented by: In = Sa.Ia + Sb.Ib + Where In = nominal rating of device Sa, Sb,... = s-factor for lamps type A, B etc. Ia, Ib,... = total circuit current for all lamps type A, B etc. For some other load types, or where no s-factor has been input, Field will have insufficient data to ensure that the rating it selects will cope with the inrush current or to check the rating if set by the user Discrimination Where adequate data are available a rating will be selected to discriminate with all downstream devices. Discrimination is determined in two ways: a) By reference to tables of predetermined relationships between various ratings (see Protective device data discrimination between fuses). b) By comparison of time/current characteristics. This is primarily used to compare curves of different device types, but will work for any combination of types and ratings. If the two curves cross or the margin of discrimination is less than 25%, the rating for the upstream device is increased. Where devices have an instantaneous trip current, such as MCB's, the curves are only compared as far as the instantaneous trip current of the downstream device; this avoids increasing the rating unnecessarily when two curves will inevitably cross, as with a fuse discriminating against an MCB. A check is later made that the intersection current is above the maximum prospective short-circuit current at that level in the network. Where insufficient data are available, Field will not attempt to ensure that the rating it selects is adequate for discrimination. VE 2015 Field 81

82 Standard Circuits Field is using and the old Appendix 5 (now removed) of the 15th. Edition of the IEE Regulations. For standard circuits type A1 from the rating is selected at 30 or 32A to conform to For standard circuits, type A2 or A3 from the old Appendix 5, the rating is selected to conform to Table 5A. If the user has set the design load a warning will be given if it exceeds the rating (with rating margin fixed at 1.0), but no other checks are made Ratings Set by User Where the rating has been set by the user, a warning will be given if it does not satisfy all the criteria for rating selection, or if Field has inadequate data to make a check Fused Connection Units At present Field does not select the BS1362 fuse rating to account for the design current and starting or inrush current of the load, or discrimination with any device in the equipment Socket Circuits This applies to socket circuits which are not standard circuits type A1, A2 and A3 ( and Appendix 5, 15th. Edition). Where only one socket outlet is connected and the device type set by the user includes a rating equal to that of the socket outlet, Field will select that rating. For all other cases the user must set the rating Cable Sizing/Checking Basic Factors The cable-sizing checks for each circuit use the following criteria: a) Current-carrying capacity of the cable. b) Voltage drop within the circuit. c) Overall voltage drop at the load end of the circuit. d) Short-circuit conditions. e) Earth-fault conditions. VE 2015 Field 82

83 The checks proceed in the above order. The selected size and number will satisfy as many as possible of these criteria, provided that Field keeps the cable size or number of parallel cables within the appropriate limits. The type of cable for each circuit can be entered, but not the cable size or the number of parallel cables. However, maximum and minimum limits for these values can be entered or left as zero. To fix the size or number, the size may be entered for both the maximum and minimum limits; Field is then constrained to use that value for the size or number. Of course, cable sizes are also limited by the maximum and minimum sizes available for the cable type concerned (installation method, phase, number of cables and number of cores per cable are taken into account). Also, for certain standard circuit types (A1, A2 or A3 final circuits) there are limits laid down in and Appendix 5, IEE 15th. Edition. Finally, parallel cables are NOT allowed in these special circuits or in ring circuits, so the number of cables is limited to one. If the cable-sizing check for a particular criterion is satisfied, it moves on to the next criterion. Otherwise the following occurs: The next available size is chosen if possible and the checks restart at criterion (a). Otherwise if the number can be increased (and if it would help) it is increased by one (the size is usually set back to the value determined for the previous criterion) and the checks restart at criterion (a). Otherwise an error or warning message is given. (An error or warning message will also be given if there is inadequate data to check the criterion.) The checks finish when an adequate size and number are found which satisfy all the criteria or the limits are finally reached and the error or warning message is given. Other calculations are also made to select or check the length of the cable and the size and length of each conductor comprising the CPC. No attempt is made to resize a cable to satisfy criterion (c), since this requires the user to make a decision about whether to increase the size of this cable or that of one of the upstream distribution cables. The length of a final circuit, however, if not set by the user, will be calculated in order to satisfy criterion (c). The cable may be resized to satisfy criterion (e), i.e. to withstand the earth-fault current, but the only CPC conductor that will be resized for this criterion is a separate cable used as the CPC or as part of the CPC. This is sized to withstand the earthfault current (or the relevant proportion thereof). The user must fix other CPC conductor sizes. VE 2015 Field 83

84 Current-carrying Capacity The basic current (In) used to select the cable sizes is set equal to the device rating for a radial circuit, and to 2/3 of the device rating for a ring circuit. For a final circuit connected to a single motor, with overcurrent trip, In is set equal to the current at which the trip will operate. The circuit design current (IB) is set equal to In for a standard type A1, A2 or A3 final circuit ( and Appendix 5, 15th. Edition), and otherwise to the calculated design current for the circuit or the value set by the user. Appendix 4 of BS 7671 gives equations for the sizing of cables with regard to current-carrying capacity for normal and overload conditions. Field usually uses a generalised equation: Equivalent to equations (1), (2), (5) or (6), but is referred to as equation (2) for convenience: (2) It >= In FF Ca Ci Cg 1.45 Where FF is the fusing factor (normally 1.45, but 2 for BS3036 fuses), and Ca, Ci and Cg are correction factors for ambient temperature, thermal insulation and grouping. However, if the circuit is grouped with other circuits and they are not liable to simultaneous overload, Appendix 4 of BS 7671 allows the use of alternate equations. In this situation Field uses two generalised equations: Equivalent to (3) or (7), but referred to as equation (3) for convenience: (3) It >= IB Ca Ci Cg Equivalent to (4) or (8), but referred to as equation (4) for convenience: (4) It >= 1 ( In² FF² + IB² 1 - Cg²) 1.45 Ca Ci Cg² In and IB are used as in Appendix 4 of BS 7671 to calculate the corrected currentcarrying capacity (equation (2), or the more stringent of equations (3) and (4), as requested by the user). This is then used to select the smallest cable of the required type and installation method with the required capacity. VE 2015 Field 84

85 Circuit Voltage Drop This is only performed if the maximum length is known (see Cable sizing/checking maximum length). The voltage drop in the circuit is calculated from the tabulated resistive and reactive voltage drops (mv/am, for the cable, phase and installation method), its length (as set by the user for the voltage drop calculation), the design current IB, the power factor and the nominal voltage. The tabulated resistive voltage drop is corrected for temperature (Appendix 4, equation (10), BS 7671). With the reactive component it constitutes a temperaturecorrected vector. The scalar product of this vector and the vector for the design current IB and power factor is the magnitude of the resultant voltage drop per metre. This is multiplied by the length and 100 and divided by the nominal voltage to get the percentage circuit voltage drop. (This is a more explicit statement of Appendix 4, section 7.3, of BS 7671.) Since the tabulated three-phase values are for balanced circuits, the neutral current is included if the circuit is unbalanced. If the circuit is from a busbar the contributions from the resistance and reactance per metre of the live and neutral conductors in the busbar and the currents in each section of the busbar as it changes between take-off points are added to the cable voltage drop. At present the power factor of the current in each busbar conductor is not calculated, but it is assumed to be lined up with the phase angle of the busbar conductor's impedance, so that, effectively, no power factor correction as mentioned in BS 7671 takes place. The final voltage drop in the circuit is compared to the limit value, and if this is exceeded the cable size is increased to the next available size and the exercise is repeated until this criterion is satisfied, if possible. Overall voltage drop is calculated by adding up all the resistive and reactive contributions separately, and taking the scalar product of the resultant voltage drop vector with the current. This is only used for checking cables, not for sizing them (see Cable sizing/checking basic factors) Short Circuit This calculation is performed in two main stages: A) Calculate minimum short-circuit current, i.e. at load end of circuit, and check the cable can withstand the energy generated until the device disconnects. B) Calculate maximum short-circuit current, i.e. at supply end of circuit, and check that this is less than the breaking capacity of the device if it is an instantaneous trip device, and that each parallel cable can withstand the energy let-through of the device and upstream device. Both stages are skipped if the device is not a BS88 or other HRC fuse or an instantaneous trip device, and a suitable warning is given. VE 2015 Field 85

86 The cable resistance is obtained from the relevant table in Conductor data - impedances and corrected to a particular temperature depending on the calculation, either minimum temperature, running temperature or mean fault temperature (i.e. the mean of the running temperature and the maximum permitted final operating temperature). The relevant resistance-temperature coefficient for the conductor material is used to obtain the correction factor. The reactances are obtained from the relevant table in Conductor data - impedances. If no reactance is available in the table, then for a cable over 35 mm² it is calculated assuming an inductance of 0.2 mh/km (zero for smaller cables). If the circuit is from a busbar the resistances and reactances of the sections of the busbar live and neutral conductors from the end-feed to the circuit take-off are included. The k-factors are obtained from the cable database. When inputting the data, the user either set these values explicitly or used the default values calculated from the normal and final operating temperatures. Details of this calculation are given in Cable sizing/checking k-factors. Stage (a) is only performed if the maximum length is known (see Cable sizing/checking maximum length). The maximum short-circuit impedance at the load end of the cable is first calculated by adding vectorially the circuit impedance to the overall upstream impedance already calculated (calculations start at the supply and work down to the final circuits). The upstream impedance is at normal running temperature and the circuit impedance is at the mean fault temperature (see Appendix 17 of the IEE Regulations, 15th. Edition). The minimum possible fault current is then calculated from this value (it also depends on the circuit phase). If the device is an instantaneous trip device and the current can trip it instantaneously the rest of stage (a) is skipped. Otherwise Field checks that the cable can withstand this current until the device trips, resizing if necessary and possible. If the trip time exceeds 5 s the check is made against the 5 s point on the characteristic curve. If it is less than 0.01 s the cable is checked against the energy let-through of the device (as supplied by the manufacturer) instead of the calculated value of current squared x trip time. Stage (b) calculates the minimum short-circuit impedance at the supply end of the cable, and hence the maximum short-circuit current. This does not depend on the cable, only on the upstream impedances (corrected to the minimum expected ambient temperature during short circuit). The calculation now depends on the types of the device and the one upstream: For BS88 and other HRC fuses, the disconnect time is obtained. If this is less than 0.1 s Field checks that the cable can withstand the energy let-through of the fuse (data from manufacturer), resizing if necessary and possible. If the cable is paralleled Field checks that each cable can withstand the minimum short-circuit current at the supply end of the cable until the fuse disconnects, resizing if necessary and possible. This current is merely due to the upstream impedance at normal running temperature with no contribution from this circuit. VE 2015 Field 86

87 For instantaneous trip devices with an upstream fuse, the maximum shortcircuit current is checked to see whether it exceeds the breaking capacity of the device. If so, and the intersection current also exceeds the breaking capacity of the device, the calculation stops with a warning. Otherwise Field checks that the cable (or each parallel cable) can withstand the intersection current or the maximum short-circuit current, whichever is smaller, until the instantaneous trip occurs, resizing if necessary and possible, and that the cable can withstand the energy let-through of the upstream fuse (manufacturer's data), resizing if necessary and possible. For instantaneous trip devices with a similar device upstream, the maximum short-circuit current is checked to see whether it exceeds the breaking capacity of the device (as above). If so, the calculation stops with a warning. Otherwise Field checks whether the cable (or each parallel cable) can withstand the maximum short-circuit current until the device trips, resizing if necessary and possible, and if the upstream device is also current-limiting it checks whether the cable (or each parallel cable) can withstand the energy let-through of the upstream device (data from manufacturer), resizing if necessary Earth Fault This calculation is only performed if the maximum length of circuit is known (see Cable sizing/checking maximum length). The size, and resistance and reactance (per metre), of the protective conductor are obtained differently for each conductor type (all resistances are now calculated at normal running temperature): For steel armour, the resistance, given the phase conductor size and number of conductors, is obtained from the relevant table in Conductor data - impedances. The reactance is assumed to be 0.3 m. The minimum armour size is calculated from the resistance using the resistivity of steel. A warning is given if any other type of insulation is present or if the armour is aluminium. For copper sheath on mineral-insulated cables, the relevant table in Conductor data - impedances gives the maximum resistances for light & heavy duty cables. The reactance is assumed to be 0.3 m. The minimum size of the sheath is calculated from the resistance using the resistivity of copper. For a core of the cable the size is obtained using BS6004 if this applies. If not, or if it does not cover the required phase conductor size, the user is warned and asked to set a size. The resistance and reactance are then obtained as for a phase conductor. VE 2015 Field 87