What is the minimum value of insulation resistance of an electrical equipment so we can give it in service?

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Well " insulation resistance"  this is very basic term in electrical world. 

If some motor, switchgear, transformer trip in Earth fault then we need to check the insulation resistance of the equipment with megger. 

For LT equipment we use 500volt megger. Our equipment is generally of 415 volt ac. So the minimum IR value formula is 

IR min. = KV +1 Mega ohm

SO if the voltage is 415 vac then min. Value of IR  will be

IR  = 0.415 +1 Mega ohm 

     = 1.415 Mega ohm.

If voltage level is 11kv then min. Value of insulation resistance will be

IR min. = 11kv + 1 Mega oh

              = 12 Mega ohm.



If any queries please comment.

Thanks.

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