Electrical Thumb Rules

Wednesday, 20 August 2014 13:31 administrator
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Size of Cable on Secondary Side of Transformer (11KV/433V)
Ref: KSEI Handbook
Rating of T/C (KVA) Primary current (Amp) Secondary Current (Amp) Min. Size of Neutral Earthing Conductor (mm2) Minimum Size of Cable (mm2)
63 3.3 84 25X3 50mm2
100 5.25 133.3 25X3 95mm2 or (2×50 mm2)
160 8.4 213.3 25X3 185mm2 or (2×95 mm2)
200 10.49 266.6 25X3 300mm2 or (2×120 mm2)
250 13.12 333 25X3 2×185 mm2
315 16.53 420 31X3 or 25X4 (2×300 mm2) or (3×185 mm2)
400 21.80 533 38X3 (3×300 mm2) or (2×400 mm2)
500 26.20 666.5 25X6 (3×400 mm2) or (4×240 mm2)
630 33 840 31X6 4×400 mm2
750 39.36 1000 50X4 Bus Bar Trucking (min. Isc 50KA)
1000 52.50 1333 210mm2 Bus Bar Trucking (min. Isc 50KA)
1250 65.50 1667 290mm2 Bus Bar Trucking (min. Isc 50KA)
1600 83.98 2133 380mm2 Bus Bar Trucking (min. Isc 50KA)
2000 105.00 2666 450mm2 Bus Bar Trucking (min. Isc 50KA)

 

HT Fuse on Primary Side of Transformer (11KV/433V)
Rating of T/C (KVA) Primary current (Amp) Secondary Current (Amp) HT Fuse
Min (Amp) Max(Amp)
63 3.3 84 10 16
100 5.25 133.3 16 25
160 8.4 213.3 16 40
200 10.49 266.6 25 40
250 13.12 333 32 40
315 16.53 420 40 63
400 21.80 533 40 63
500 26.20 666.5 50 100
630 33 840 63 100
750 39.36 1000 75 160
1000 52.50 1333 100 160
1250 65.50 1667 100 200
1600 83.98 2133 160 250
2000 105.00 2666 200 250

Capacitor Bank for Power Supply Voltage
System Voltage Minimum rating of capacitor bank
3.3 KV , 6.6KV 75 Kvar
11 KV 200 Kvar
22 KV 400 Kvar
33 KV 600 Kvar

Capacities of PVC conduits
Nominal conductor Size mm 16 mm 20 mm 25 mm 32 mm
Number of Cables (maximum)
1.0 6 5 19 30
1.5 5 4 15