Version 2012 This reference manual contains examples on how to use CableCALC Pro BS electrical software which is used for designing electrical installations in accordance with British Standard 7671:2008 (IEE Wiring Regulations 17th Ed.) and IEC 60364.
Table of contents 1. Example 1: Flat two-core, Clipped direct .............................................................. 3
1.1 Problem ........................................................................................................... 3
1.1 Problem A 230 V single-phase radial circuit is to be run in flat two-core (with cpc) 70 ˚C thermoplastic insulated and sheathed cable having copper conductors clipped direct and not grouped with the cables of other circuits. The circuit is to be protected by a BS 88-2.2 ‘gG’ fuse against overload and short circuit. If Ib = 42 A, l = 27 m, ta = 40 ˚C, Ze = 0.35 and the short-circuit current at the point of supply is 4 kA determine the nominal rating of the fuse and minimum conductor cross-sectional area if the voltage drop is not to exceed 4 % of the nominal voltage.
1.2 Solution By hand, the iterative process of solving this example can take hours. Using the software it is solved within minutes, or even seconds. Data entry is flexible in that it can be entered into the program by the user in any order. However, it is best to start with the cable data and the installation method as this affects other outputs such as the correction factor calculations.
1.2.1 Cable From the Cable tab set the control values according to Table 1. Set the Installation method to C Clipped Direct. See Figure 1.
Table 1. Example 1 – Cable tab control values
Control Name Value Phases 1 Φ Cores Multi-core Material Copper Armour Armoured Insulation Thermoplastic Flat (70 ˚C)
1.2.2 Load Next go to the Load tab and set the load current to 42 A. As per Table 2 the circuit arrangement is Radial, Power Factor is 1 and Efficiency is 100 %.
Table 2. Example 1 – Load tab control values
Control Name Value Power/Current CurrentAmps 42 A Efficiency 100 % Power Factor 1 Circuit Arrangement Radial
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1.2.3 Supply From the supply tab set the Voltage Drop (%) to 4 %, Length = 27 m, Upstream Fault Level = 4 kA, Impedance, Ze = 0.35 .
Table 3. Example 1 – Supply tab control values.
Control Name Value Comments Voltage ph-e 230 V 1Φ and 3Φ supply default is 230 Vpn and 400 Vpp.Voltage Drop 4 % Use VD? True Length 27 m Upstream Fault Level 4 kA Impedance, Ze 0.35 Frequency 50 Hz System Grounding TN-C-S Notes:
- Right-click the Impedance, Ze control for information on typical source impedance values to be used.
- Although in reality the upstream fault level and the source impedance are related by Ohm’s Law they are usually specified as separate values.
Figure 3. Supply - user inputs
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1.2.4 Correction Go to the Correction tab and press the Ambient temperature, Ca button to open the appropriate calculation program. Set the ambient temperature to 40 degrees Celsius. This results in a calculated ambient temperature correction factor equal to 0.87.
Figure 4. Example 1 - Ambient temperature correction factor Ca calculation
1.2.5 Protection Go to the Protection tab and select the type of protection device. Open (+)Cartridge Fuses → (+)HRC Fuse (BS 88) → 50 A. Table 4. Example 1 – protection tab control values
Control Name
Value Comments
Protection provided
Overload and Short-circuit protection
Design current for sizing cables, Ib when protection provided is (a) Overload and Short-circuit protection → Ib = Nominal current of protective device In; or (b) Short-circuit protection only → Ib = Load current.
Circuit protective device
Cartridge Fuses\HRC Fuse (BS 88)\50 A
Short-circuit clearing time
0.5 s Accurate values obtained from manufacturers curves based on calculated fault currents.
Earth fault clearing time
0.5 s
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1.3.1 Phase conductor The minimum conductor size required is 10 mm2 which has a tabulated current-carrying capacity of 64 A with an effective current-carrying capacity (de-rated) of 55.7 A. The actual voltage drop is 2.08 %. Note for small conductor sizes the short-circuit performance would be the main influence on the minimum conductor size requires if the short-circuit clearing time and/or the upstream fault level were greater.
1.3.2 Earth conductor The standard earth conductor size for this type and size of cable is 4 mm2. By default the program specifies a 10 mm2 earth cable size based on Table 54-7 from BS 7671. In many cases a smaller earth cable size can be used. The user should manually specify the earth cable size to be used and check for compliance with earth fault loop impedance and short-circuit performance. In this case the standard 4 mm2 earth cable is compliant.
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2 Example 2: Single-core thermosetting, In trunking
2.1 Problem A 230 V single-phase circuit is to be run in single-core 90 ˚C thermosetting cables having copper conductors, in trunking with five other similar circuits. The circuit is to be protected by a BS 88-2.2 ‘gG’ fuse against overload and short-circuit. If Ib = 38 A, l = 90 m, ta = 45 ˚C, Ze = 0.8 and the power factor of the load is 0.8 lagging and the short-circuit current at the point of supply is 6 kA determine the minimum conductor cross-sectional area if the voltage drop is not to exceed 2.5 % of the nominal voltage.
2.2 Solution
2.2.1 Cable From the Cable tab set the control values according to Table 5. Set the Installation method to B Enclosed in conduit on a wall or in trunking.
Table 5. Example 2 – Cable tab control values
Control Name Value Phases 1 Φ Cores Single-core Material Copper Armour Non-armoured Insulation Thermosetting (90 ˚C)
2.2.2 Load Next go to the Load tab and set the load current to 38 A. As per Table 6 the circuit arrangement is Radial, Power Factor is 0.8 and Efficiency is 100 %.
Table 6. Example 2 – Load tab control values
Control Name Value Power/Current CurrentAmps 38 A Efficiency 100 % Power Factor 0.8 Circuit Arrangement Radial
2.2.3 Supply From the supply tab set the Voltage Drop (%) to 2.5 %, Length = 90 m, Upstream Fault Level = 6 kA, Impedance, Ze = 0.8 .
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Control Name Value Voltage ph-e 230 V Voltage Drop 2.5 % Use VD? True Length 90 m Upstream Fault Level 6 kA Impedance, Ze 0.8 Frequency 50 Hz System Grounding TN-C-S
2.2.4 Correction Go to the Correction tab and press the Ambient temperature, Ca button to open the appropriate calculation program. Set the ambient temperature to 45 degrees Celsius which results in a calculated correction factor Ca = 0.87. Press the Grouping, Cg button and set the no. of circuits to 6 which results in a calculated correction factor Cg = 0.57. The overall correction factor (displayed) is equal to Ca * Cg = 0.496. Note to reset all correction factors, right-click Overall Correction Factor and select Reinitialise to Default Value.
Figure 6. Example 2 – Correction factor for Grouping, Cg. Note that the total No. of (grouped) circuits includes the cable being calculated (1) plus (+) the five (5) other circuits.
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2.2.5 Protection Go to the Protection tab and select the type of protection device. Open (+)Cartridge Fuses → (+)HRC Fuse (BS 88) → 40 A.
Table 7. Example 2 – Protection tab control values.
Control Name Value Protection provided Overload and Short-circuit protection Circuit protective device Cartridge Fuses\HRC Fuse (BS 88)\40 A Short-circuit clearing time 1 s Earth fault clearing time 1 s
2.3 Results
2.3.1 Phase conductor The minimum conductor size required is 25 mm2 which has a tabulated current-carrying capacity of 133 A with an effective current-carrying capacity (de-rated) of 66 A. The actual voltage drop is 2.41 %.
2.3.2 Earth conductor By default the program specifies a 16 mm2 earth cable size based on Table 54-7 from BS 7671. In many cases a smaller earth cable size can be used. The user should manually specify the earth cable size to be used and check for compliance with earth fault loop impedance and short-circuit performance. In this case a 6 mm2 earth cable satisfies earth fault loop and short-circuit performance requirements.
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3.1 Problem A 400 V three-phase circuit is to be run in multi-core 90 ˚C thermosetting and sheathed cables having copper conductors and is protected against overload and short-circuit by a 40 A BS 88-2.2 ‘gG’ fuse. The cable will be direct buried at a depth of 0.5 meters across a ‘brown field’ site where the soil conditions are not known. If Ib = 35 A, l = 55 m, soil ambient temperature ta = 25 ˚C, Ze = 0.35 and the power factor of the load is 0.9 lagging and the short-circuit current at the point of supply is 6 kA determine the minimum conductor cross-sectional area if the voltage drop is not to exceed 2.5 % of the nominal voltage.
3.2 Solution
3.2.1 Cable From the Cable tab set the control values according to Table 5. Set the Installation method to D Direct in ground or in ducting in ground, in or around buildings.
Table 8. Example 3 – Cable tab control values
Control Name Value Phases 3 Φ Cores Multi-core Material Copper Armour Armoured Insulation Thermosetting (90 ˚C)
3.2.2 Load Next go to the Load tab and set the load current to 35 A. As per Table 6 the circuit arrangement is Radial, Power Factor is 0.9 and Efficiency is 100 %.
Table 9. Example 3 – Load tab control values
Control Name Value Power/Current CurrentAmps 38 A Efficiency 100 % Power Factor 0.9 Circuit Arrangement Radial
3.2.3 Supply From the supply tab set the Voltage Drop (%) to 2.5 %, Length = 55 m, Upstream Fault Level = 6 kA, Impedance, Ze = 0.35 .
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Control Name Value Voltage ph-ph 400 V Voltage Drop 2.5 % Use VD? True Length 55 m Upstream Fault Level 6 kA Impedance, Ze 0.35 Frequency 50 Hz System Grounding TN-C-S
3.2.4 Correction Go to the Correction tab and press the Depth of burial, Cb button. Set the depth of burial to 0.5 metres which results in a calculated correction factor Cb = 1.04. Set the correction factor for Ambient temperature, Ca to soil ambient temperature of 25 degrees Celsius which results in a calculated correction factor Ca = 0.96. The soil conditions are not known, but because of the nature of the site the soil thermal conductivity is assumed to be poor. The tabulated current-carrying capacities for buried cables by default assume 2.5 K.m/W; which is poor. Therefore the correction factor for thermal resistivity of soil (Cs) can remain equal to 1. The overload factor for BS 88-2.2 fuse is 1.45; thus overload for buried cables (Cc) is set automatically by the program equal to 0.9 (Regulation 433.1.4 in BS 7671:2008).
Figure 7. Example 3 – Correction factor for Depth of burial, Cb. Note correction factor >1 (i.e. effective current-carrying capacity increased) for shallower (than default 0.8 m) depth of burial.
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3.2.5 Protection Go to the Protection tab and select the type of protection device. Open (+)Cartridge Fuses → (+)HRC Fuse (BS 88) → 40 A.
Table 10. Example 2 – Protection tab control values.
Control Name Value Protection provided Overload and Short-circuit protection Circuit protective device Cartridge Fuses\HRC Fuse (BS 88)\40 A Short-circuit clearing time 1 s Earth fault clearing time 1 s
3.3 Results
3.3.1 Phase conductor The minimum conductor size required is 10 mm2 which has a tabulated current-carrying capacity of 58 A with an effective current-carrying capacity (de-rated) of 52.1 A. The actual voltage drop is 2.48 %.
3.3.2 Earth conductor By default the program specifies a 10 mm2 earth cable size based on Table 54-7 from BS 7671. In many cases a smaller earth cable size can be used. The user should manually specify the earth cable size to be used and check for compliance with earth fault loop impedance and short-circuit performance. A 6 mm2 earth cable satisfies earth fault loop and short-circuit performance requirements.
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4.1 Problem A 400 V three-phase induction motor has a (mechanical power) rating of 10 kW at a power factor of 0.85 lagging at an efficiency of 90 %. If the motor is subject to frequent stopping and starting and the connection between a direct-on-line starter and the motor terminals is a multi-core armoured thermosetting cable with copper conductors, installed in free air, what is the minimum conductor cross-section area required?
4.2 Solution Regulation 552.1.1 (BS 7671:2008) requires that where a motor is intended for intermittent duty and for frequent starting and stopping account should be taken of the cumulative temperature rise effects on the cables feeding the motor. Furthermore, starting currents for Direct-On-Line starting (D.O.L.) can be between 5 and 8 times the full load current. CableCALC has settings which allow users to size cables for motors (between the starter and the motor terminals).
4.2.1 Cable From the Cable tab set the control values according to Table 5. Set the Installation method to D Direct in ground or in ducting in ground, in or around buildings.
Table 11. Example 3 – Cable tab control values
Control Name Value Phases 3 Φ Cores Multi-core Material Copper Armour Armoured Insulation Thermosetting (90 ˚C)
4.2.2 Load Next go to the Load tab and set the load power to 10 kW. The circuit arrangement is D.O.L. Motor, Power Factor is 0.85 and Efficiency is 90 %.
Table 12. Example 3 – Load tab control values
Control Name Value Power/Current Power Power 10 kW Efficiency 90 %
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Power Factor 0.85 Circuit Arrangement D.O.L. Motor
4.2.3 Supply From the supply tab set the Length = 25 m.
Table 7. Example 3 – Supply tab control values.
Control Name Value Voltage ph-ph 400 V Voltage Drop - Use VD? False Length 25 m Upstream Fault Level 6 kA Impedance, Ze 0.35 Frequency 50 Hz System Grounding TN-C-S
4.2.4 Correction Set the correction factor for Ambient temperature, Ca to ambient ambient temperature of 35 degrees Celsius which results in a calculated correction factor Ca = 0.96.
4.2.5 Protection Go to the Protection tab and select the type of protection device. Open (+)Miniature Circuit Breaker (MCB) → (+)Type C (BS EN 60898) → 20 A.
Table 13. Example 2 – Protection tab control values.
Control Name Value Protection provided Short-circuit protection only Circuit protective device
Miniature Circuit Breaker (MCB)\Type C (BS EN 60898)\20 A
Short-circuit clearing time
0.25 s
Earth fault clearing time
0.25 s
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4.3.1 Phase conductor The minimum conductor size required is 2.5 mm2 which has a tabulated current-carrying capacity of 33 A with an effective current-carrying capacity (de-rated) of 31.7 A. Note the minimum phase conductor size is sensitive to the short-circuit fault clearing time (motors are typically protected from thermal overload).
4.3.2 Earth conductor The earth cable should have a minimum cross-sectional area of 1.5 mm2.
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