Reduced Service Entrance Netural Size

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mull982

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I am looking at an existing existing 4000A service that has 10 sets of 500MCM cables however the neutrals are only 10 sets of 4/0 cables. This is an older installation and now that the main switchboard is being replaced I'm wondering if larger neutral's have to be run with the existing 10 sets of 500MCM feeders?

I was always under the impression that the NEC required neutral to be same size as phase conductors however there were articles that allowed for using a smaller neutral. NEC 250.24 comes to mind.

Can someone tell me what is required for service entrance neutral conductors and what sections can be applied for using a reduced neutral. Does a reduced 4/0 neutral sound right for this instance?

Thanks
 
mull982 said:
I am looking at an existing existing 4000A service that has 10 sets of 500MCM cables however the neutrals are only 10 sets of 4/0 cables. This is an older installation and now that the main switchboard is being replaced I'm wondering if larger neutral's have to be run with the existing 10 sets of 500MCM feeders?

I was always under the impression that the NEC required neutral to be same size as phase conductors however there were articles that allowed for using a smaller neutral. NEC 250.24 comes to mind.

Can someone tell me what is required for service entrance neutral conductors and what sections can be applied for using a reduced neutral. Does a reduced 4/0 neutral sound right for this instance?

Thanks
Click to expand...

See 220.61:

220.61 Feeder or Service Neutral Load.
 
mull982 said:
I am looking at an existing existing 4000A service that has 10 sets of 500MCM cables however the neutrals are only 10 sets of 4/0 cables. This is an older installation and now that the main switchboard is being replaced I'm wondering if larger neutral's have to be run with the existing 10 sets of 500MCM feeders?

I was always under the impression that the NEC required neutral to be same size as phase conductors however there were articles that allowed for using a smaller neutral. NEC 250.24 comes to mind.

Can someone tell me what is required for service entrance neutral conductors and what sections can be applied for using a reduced neutral. Does a reduced 4/0 neutral sound right for this instance?

Thanks
Click to expand...
The minimum grounded service conductor must be per 250.24(C)(2) (assuming your calculated neutral load per Art. 220.61 does not exceed this). Grounded conductors used as service conductors only need to be sized for the largest ungrounded conductor in each raceway (but must comply with 220.61). Per Table 250.66 a 500 MCM CU ungrounded conductor would need at at least a 1/0 grounded conductor, so your 4/0 are fine as long as you don't have neutral load that exceeds this.
 
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