# Earthing strip size calculation.

Home Electrical Engineering Forum General Discussion Earthing strip size calculation.

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• #10700
shridhar awasthi
Participant

Dear all …. m shridhar awasthi having 3 year's of experiecnce in MEP-field. so this time i m facing lot's of interview's to get better opportunity.

So it happened in one of them… interviewer whe asked to me about the Earth strip size calculation….i replied-earth strip size should be half of phase conductor size….

But he replied there should be any formula to get exact size…if suppose u are going to earth a pannel..u used copper cable and want to earth through GI strip…so would this do work??…if no…then hw would we get earth strip size..

Kindly suggest and help me to enhance my knowledge.

Thanks

#12695
Keymaster

If I understand this correctly you are going to ground a panel.  In the USA we follow the National Electric Code.  Per the code, the minimum size equipment grounding conductor is dictated by a table in the NEC.  Section 250, table 250.122.  It is based on the overcurrent protection on conductors feeding the panel.  No calculations required. – Alton Tupa

#12699
Keymaster

If you want to get more technical, there are calculations in the IEEE standard the Green book, Standard No. 142, chapter 2.

#12691
electricalexpert65
Participant

Yes! Your interviewer was very correct! There is a very precise formula for sizing the earth strip:

S = I Root 't' / K

where, S is the cross sectional area of the earth strip, in sq.mm

I is the maximum anticipated earth fault current, in Amperes

t is the duration of the earth fault in seconds

K is a constant dependinng upon the material of the earth strip, type of insultaion & method of laying the earth strip (Pl. refer to IS 3043 for the values of these constants)

#12669
shridhar awasthi
Participant

Thanx Mr. COONOOR and Mr.Alton to guide me thanx alot

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