ELECTRICAL AND MECHANICAL WORKS
CABLE SIZING CALCULATION FOR LVB
Supply voltage 220 V
Fault Level 24 MVA
Voltage drop limit 1.5 %
Cable Type Description British Standard
A 4/C XLPE/SWA/LSOH BS5467 BS6724
B 3/C XLPE/SWA/LSOH BS5467 BS6724
C 2/C XLPE/SWA/LSOH BS5467 BS6724
D 1/C XLPE/SWA/LSOH BS5467 REMARK
E 4/C FR/SWA/LSOH BS6387 Cat.C.W.Z.
F 3/C FR/SWA/LSOH BS6387 Cat.C.W.Z. V Volt drop higher than limit.
G 2/C FR/SWA/LSOH BS6387 Cat.C.W.Z. A Cable rating lower than protective device rating.
H 1/C FR/SWA/LSOH BS6387 Cat.C.W.Z. T Cable type not suitable.
I 1/C LSHF BS5467 BS7211 E1 Earth fault relay is needed to trip the protective device for 5s disconnection
J 1/C FR/LSHF BS6387 Cat.C.W.Z. E2 Earth fault relay is needed to trip the protective device for 0.4s disconnection
K 4/C XLPE/SWA/LSHF with moulded outlets K Let-through energy of protective device will damage cable
L 2/C XLPE/SWA/LSHF with moulded outlets KK Let-through energy of protective device will damage protective conductor
M 1/C PVC BS6004 S Touch voltage for 5s disconnection > 50V
CIRCUITRY CABLE PROTECTIVE DEVICE EARTHING Remark
of Protective
Rating of BS 88 back-up
Max. Prospective fault for
Calculated Cable Rating
Max. earth fault loop
Max. earth fault loop
loop
RCD of 30mA in
Calculated Voltage Drop
Device (A) (MCB /
Type ( Cable / Armour /
5s
Touch voltage for 5s
0.4s
impedance at fault (ohm)
disconnecton time (ohm)
disconnecton time (ohm)
sensitivity is employed
No.of Cable per phase
MCCB / BS88 Fuse)
Connected Load (A)
Length of Cable (m)
Type ( B / 3 / Fuse )
for
disconnection (V)
for
downstream (kA)
Cable size (mm²)
fault
No.of Phase
Cable Type
Size (mm²)
impedance
impedance
fuse (A)
Rating
Tape )
Earth
(%)
(A)
Cable No. From To
A01 LVB-3-1 eg 1 25.00 1. C 50. 1. 100. 32. 3 N/A N/A Armour N/A 190 1.14 3 1.528 0.688 0.357 42
A02 LVB-3-1 eg 2 25. 3. A 10. 1. 50 32. 3 N/A N/A Armour N/A 65 1.31 2 1.528 0.688 0.381 34
A18 LVB-3-1 eg 3 25.00 1. C 100. 1. 100. 32. Fuse N/A N/A Cable 6 296 0.59 5 1.760 0.688 0.422 49
A19 LVB-3-1 eg 4 25. 3. A 10. 1. 50 32. Fuse N/A N/A Cable 4 65 1.31 2 1.760 0.688 0.439 37
A03 LVB-3-1 eg 5 230. 3. A 240. 4. 450 250. 3 N/A N/A Tape 50x6 1,824 1.43 13 0.196 0.088 0.060 50
A05 LVB-3-1 SB-3-801 62.24 3. E 120. 1. 52 250. 3 N/A N/A Tape 50x6 295 0.31 17 0.196 0.088 0.020 6
A06 LVB-3-1 ISO-3-801 15.15 1. C 16. 1. 52 63. 3 N/A N/A Tape 50x6 96 1.04 2 0.776 0.349 0.101 1
A07 LVB-3-1 MCC-1-5 293.32 3. E 300. 1. 89 400. 3 N/A N/A Tape 50x6 525 1.27 16 0.122 0.055 0.022 16
A08 LVB-3-1 Capacitor bank 227.27 3. A 240. 1. 24 400. 3 N/A N/A Tape 50x6 456 0.30 28 0.122 0.055 0.009 4
A09 LVB-3-1 LVB-3-2 889.39 3. E 400. 2. 36 1,000. 3 N/A N/A Tape 50x6 1,216 0.71 30 0.049 0.022 0.008 16
A10 LVB-3-1 Capacitor bank 303.03 3. A 400. 1. 24 500. 3 N/A N/A Tape 50x6 608 0.32 28 0.122 0.055 0.008 4
A11 LVB-3-1 MCC-1-6 291.12 3. E 300. 1. 81 400. 3 N/A N/A Tape 50x6 525 1.14 17 0.122 0.055 0.020 14
A12 LVB-3-1 SB-2-602 48.08 3. E 240. 1. 72 400. 3 N/A N/A Tape 50x6 456 0.19 18 0.122 0.055 0.020 13
A13 LVB-3-1 ATS of UPS-1-01 166.67 3. E 150. 1. 83 250. 3 N/A N/A Tape 50x6 339 1.09 14 0.196 0.088 0.028 9
A15 LVB-3-1 DBP-1-222 22.73 3. A 70. 1. 81 160. 3 N/A N/A Tape 50x6 210 0.29 9 0.306 0.138 0.044 6
A14 LVB-3-1 SB-2-502 13.39 3. E 120. 1. 145 250. 3 N/A N/A Tape 50x6 295 0.19 8 0.196 0.088 0.052 16
REMARK
1 Grouping factor 0.87 is based on assumption of 5 groups cable spaced with one diameter.
2 Ambient temperature is assumed to be 40 deg.C.
3 Volt-drop limit to be 1.5 %. ( volt-drop limit for final circuit is 2.5% )
4 50 x 6 mm bare copper tape is used as protective conductor between main switchboards and panel boards.
Cable armour or separate conductor is used as protective conductor for final or sub-final circuits.
CONCLUSION
1 Those cables with V in remark are undersized regarding the limit in voltage drop.
2 Those cables with A in remark are undersized as they are not protected by the protective device.
3 For those circuits with E1 in remark, either the earth fault loop impedance should be decreased or earth fault relay should be provided.
4 For those circuits with S in remark, either the CPC impedance should be decreased or earth fault relay should be provided.
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Cable Insulation Material Thermosetting
resistive
correction
factor from
cable resistive
cross- operating correction
sectional temp. to factor from k value for k value for
PVC 2 area 20C 20C to fault cable armour
Rubber 85 8 1 0.78 1.6 143 46
Thermosetting 14 300 0.78 1.6 143 46
Part of Table 43A
PVC 70 Rubber 85 Thermosetting
Correctio Correction k value
cross- Max. Correction n factor Max. Correction factor for Max. Correction Correction k value k value
sectional conductor temp limiting final factor from from 70C k value for k value for conductor limiting final factor from from 85C k value steel conductor limiting final factor from factor from for for
area (C) temp (C) 20C to fault to 20C cable steel armour temp (C) temp (C) 85C to fault to 20C for cable armour temp (C) temp (C) 90C to fault 90C to 20C cable armour
1 70 160 1.38 0.83 115 51 85 220 1.53 0.79 134 51 90 250 1.6 0.78 143 46
300 70 140 1.34 0.83 103 51 85 220 1.53 0.79 134 51 90 250 1.6 0.78 143 46
Type 1/C LSOH, 1/C PVC ( BS 7211 & BS 7889 ) M/C XLPE/SWA/LSOH ( BS 6387 C,W & Z )
Conduit/Trunking
Installation Method Perforated cable tray / free air
Voltage drop (mV/A/m)
Voltage drop (mV/A/m)
Voltage drop (mV/A/m)
Voltage drop (mV/A/m)
Conductor Impedance
Conductor Impedance
Conductor Impedance
Conductor Impedance
Cross-sectional area of
Armour impedance at
Armour impedance at
per phase at 20C
per phase at 20C
per phase at 20C
per phase at 20C
steel armour (mm2)
1 Phase 2/C (A)
3 Phase 4/C (A)
1 Phase 2/C (A)
3 Phase 4/C (A)
20C (ohms/km)
20C (ohms/km)
Cross-sectional
(ohms/km)
(ohms/km)
(ohms/km)
(ohms/km)
Area/mm2
K2 S 2
K2 S 2
K2 S 2
k
k
k
1 17 46 18.1 143 20449 15 40 18.1 143 20449 0 0 0 0 0 0 0 0 0 0
1.5 22 31 12.1 143 46010.25 19 27 12.1 143 46010 29 31 12.053+.104i 10.2 143 46010 15 25 27 12.053+.104i 8.8
2.5 30 19 7.41 143 127806.25 26 16 7.41 143 127806 39 19 7.381+.101i 8.8 143 127806 17 33 16 7.381+.101i 7.7
4 40 12 4.61 143 327184 35 10 4.61 143 327184 52 12 4.592+0.099i 7.9 143 327184 21 44 10 4.592+0.099i 6.8
6 51 7.9 3.08 143 736164 45 6.8 3.08 143 736164 66 7.9 3.068+.094i 7 143 736164 24 56 6.8 3.068+.094i 4.3
10 71 4.7 1.83 143 2044900 63 4 1.83 143 2E+06 90 4.7 1.823+.093i 6 143 2E+06 41 78 4 1.823+.093i 3.7
16 95 2.9 1.15 143 5234944 85 2.5 1.15 143 5E+06 115 2.9 1.145+.088i 3.7 143 5E+06 42 99 2.5 1.145+.088i 3.1
25 126 1.9 0.727 143 12780625 111 1.65 0.727 143 1E+07 152 1.9 .723+.082i 3.7 143 1E+07 43 131 1.65 .723+.082i 2.3
35 156 1.35 0.524 143 25050025 138 1.15 0.524 143 3E+07 188 1.35 .522+.077i 2.6 143 3E+07 62 162 1.15 .522+.077i 2
50 189 1.05 .379+.092i 143 51122500 168 0.9 .379+.092i 143 5E+07 228 1 .386+.076i 2.3+.3i 143 5E+07 70 197 0.87 .386+.076i 1.8+.3i
70 240 0.75 .263+.088i 143 100200100 214 0.65 .263+.088i 143 1E+08 291 0.69 .267+.075i 2+.3i 143 1E+08 80 251 0.6 .267+.075i 1.2+.3i
95 290 0.58 .191+.086i 143 184552225 259 0.5 .191+.086i 143 2E+08 354 0.52 .193+.074i 1.4+.3i 143 2E+08 114 304 0.45 .193+.074i 1.1+.3i
120 336 0.48 .151+.084i 143 294465600 299 0.42 .151+.084i 143 3E+08 410 0.42 .153+.072i 1.3+.3i 143 3E+08 126 353 0.37 .153+.072i 0.76+.3i
150 375 0.43 .124+.083i 143 460102500 328 0.37 .124+.083i 143 5E+08 472 0.35 .125+.073i 1.2+.3i 143 5E+08 139 406 0.3 .125+.073i 0.68+.3i
185 426 0.37 .0995+.083i 143 699867025 370 0.32 .0995+.083i 143 7E+08 539 0.29 0.1+.073i 0.82+.3i 143 7E+08 196 463 0.26 0.1+.073i 0.61+.3i
240 500 0.33 .0764+.082i 143 1177862400 433 0.29 .0764+.082i 143 1E+09 636 0.24 .0773+.072i 0.73+.3i 143 1E+09 218 546 0.21 .0773+.072i 0.54+.3i
300 573 0.31 .062+.081i 143 1840410000 493 0.27 .062+.081i 143 2E+09 732 0.21 .0626+.072i 0.67+.3i 143 2E+09 239 628 0.185 .0626+.072i 0.49+.3i
400 915 0.2 .05+.08i 143 3271840000 840 0.16 .05+.08i 143 3E+09 847 0.195 .005+.071i 0.59+.3i 143 3E+09 279 728 0.17 .005+.071i 0.35+.3i
500 1044 0.185 .0414+.079i 143 5112250000 973 0.16 .0414+.079i 143 5E+09
630 1191 0.175 .0342+.077i 143 8116208100 1115 0.16 .0342+.077i 143 8E+09
800 1358 0.17 1275 0.155
1000 1520 0.165 1436 0.155
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2.5(Ring) 60 9.5 52 8
on tray not in trunking on tray not in trunking
Table 4E1A Table 4E1B Table 4E1A Table 4E1B Table 4E4A Table 4E4B Draka Draka Table 4E4A Table 4E4B Draka Draka
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K2 S 2
k
0 0
143 46010
143 127806
143 327184
143 736164
143 2E+06
143 5E+06
143 1E+07
143 3E+07
143 5E+07
143 1E+08
143 2E+08
143 3E+08
143 5E+08
143 7E+08
143 1E+09
143 2E+09
143 3E+09
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3d112809-10ed-4344-8762-3212619336d2.xls AC Cable - Page 5 Print Date : 11/1/2011
Size of
conduit/trunking/tape Impedance ohm/km
(mm) at 20C
16 4.75i
20 3.125i
25 2.125i
35 1.375i
50x38 2.13i
38x50 2.13i
50x50 1.77i
75x50 1.26i
50x75 1.26i
75x75 0.98i
100x50 1.1i
50x100 1.1i
100x75 0.88i
75x100 0.88i
100x100 0.63i
150x50 0.76i
50x150 0.76i
150x75 0.63i
75x150 0.63i
150x100 0.46i
100x150 0.46i
150x150 0.37i
3x25 0.2404
25x3 0.2404
6x25 0.1202
25x6 0.1202
6x50 0.0601
50x6 0.0601
Remark: heavy gauge conduit and trunking are considered.
Reactance of conduit and trunking is much greater than resistance. Hence, the temperature rise due to fault has an insignificant effect on impedance.
3d112809-10ed-4344-8762-3212619336d2.xls Earthing - Page 6 Print Date : 11/1/2011
Rating of back-up Breaking capacity of fault
Current For Disconnection (A) fuse (A) current device (kA)
Fuses (BS 88) MCB (BS 3871) 5 4.5
Rating Current for disconnection (A) Type B Type 3 160 4.5
(A) 0.1 s 0.2 s 0.4 s 5s <0.01s (let through energy A sec) <0.1s (let through energy A2sec) 5s (Max)
2
<0.1s (let through energy A2sec) 5s (Max) 200 23
5 25 20 50 9000 22.5 400 23
6 36 31 27 17 52 60 30 24 60 27 630 40
10 60 51 45 31 140 290 50 40 100 26000 45
15 N/A N/A N/A N/A N/A N/A 75 60 150 26000 67.5
16 120 95 85 55 250 570 80 64 160 72 COP table 9(2)
20 175 150 130 79 360 1100 100 80 200 30000 90
25 220 180 160 100 430 1850 125 100 250 112.5
30 150 120 300 37000 135
32 320 260 220 125 620 3400 160 128 320 144
40 400 340 280 170 810 8500 200 160 400 70000 180
50 540 450 380 220 900 13500 250 200 500 225
63 710 590 500 280 1300 24000 315 252 630 70000 283.5
80 1100 890 740 400 1500 40000 400 320 800 360
100 1400 1150 980 550 2000 60000 500 400 1000 450
125 1800 1500 1300 690 2500 85000 1250 562.5
160 2400 2000 1700 900 3500 160000 1600 720
200 3000 2500 2200 1200 4000 255000 2000 900
250 1467 6100 550000 2500 1125
315 2200
400 2444 10000 1900000 4000 1800
630 18000 5300000 6300 2835
1000 10000 4500
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Revision Date Remarks
A 17/11/03 First Issue