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