Earthing Strip / Wire / Pit Quick Reference (Part-1)
EARTHING STRIP /WIRE / PIT QUICK REFERENCE-(PART-1)
TRANSFORMER-EARTHING WIRE / STRIP SIZE:
Size of T.C or DG
Body Earthing
Neutral Earthing
<315 KVA 25×3 mm Cu / 40×6 mm GI Strip 25×3 mm Cu Strip 315 KVA to 500 KVA 25×3 mm Cu / 40×6 mm GI Strip 25×3 mm Cu Strip 500 KVA to 750 KVA 25×3 mm Cu / 40×6 mm GI Strip 40×3 mm Cu Strip 750 KVA to 1000 KVA 25×3 mm Cu / 40×6 mm GI Strip 50×3 mm Cu Strip
MOTOR- EARTHING WIRE / STRIP SIZE:
Size of Motor
Body Earthing
< 5.5 KW
85 SWG GI Wire
5.5 KW to 22 KW
25×6 mm GI Strip
22 KW to 55 KW
40×6 mm GI Strip
55 KW
50×6 mm GI Strip
PANEL- EARTHING WIRE / STRIP SIZE:
Type of Panel
Body Earthing
Lighting & Local Panel
25×6 mm GI Strip
Control & Relay Panel
25×6 mm GI Strip
D.G & Exciter Panel
50×6 mm GI Strip
D.G & T/C Neutral
50×6 mm Cu Strip
ELECTRICAL EQUIPMENT EARTHING:
Equipment
Body Earthing
LA (5KA,9KA)
25×3 mm Cu Strip
HT Switchgear
50×6 mm GI Strip
Structure
50×6 mm GI Strip
Cable Tray
50×6 mm GI Strip
Fence / Rail Gate
50×6 mm GI Strip
EARTHING WIRE (AS PER BS 7671)
Cross Section Area of Phase, Neutral Conductor(S) mm2
Minimum Cross Section area of Earthing Conductor (mm2)
S<=16
S (Not less than 2.5 mm2)
16<S<=35
16
S>35
S/2
EARTHING RESISTANCE VALUE:
Earthing Resistance Value
Power Station 0.5 Ω Sub Station Major 1.0 Ω Sub Station Minor 2.0 Ω Distribution Transformer 5.0 Ω Transmission Line 10 Ω Single Isolate Earth Pit 5.0 Ω Earthing Grid 0.5 Ω As per NEC Earthing Resistance should be <5.0 Ω