Service Entrance Neutral

[L'uomo Universale]

I have a project that has two 4000 Amp service feeds to an industrial facility serving mostly 3PH balanced loads. How much can I reduce the neutral conductor by and still be in compliance with all applicable NEC rules?

I have read through 220.61 but I am still unclear on just how much I can reduce the load by. The greatest imbalance is 9720 VA which is only 12 amps on a 480v 3ph system.

Any suggestions of additional code sections that I should consider?

Thanks,

 

[david luchini]

I have a project that has two 4000 Amp service feeds to an industrial facility serving mostly 3PH balanced loads. How much can I reduce the neutral conductor by and still be in compliance with all applicable NEC rules?

I have read through 220.61 but I am still unclear on just how much I can reduce the load by. The greatest imbalance is 9720 VA which is only 12 amps on a 480v 3ph system.

Any suggestions of additional code sections that I should consider?

Thanks,

250.24(C)

 

[texie]

I have a project that has two 4000 Amp service feeds to an industrial facility serving mostly 3PH balanced loads. How much can I reduce the neutral conductor by and still be in compliance with all applicable NEC rules?

I have read through 220.61 but I am still unclear on just how much I can reduce the load by. The greatest imbalance is 9720 VA which is only 12 amps on a 480v 3ph system.

Any suggestions of additional code sections that I should consider?

Thanks,

See 250.24(C). The intent is to have a grounded conductor large enough to carry the fault current. In other words, it has to be big enough to carry the load or if the load is small like yours it must be big enough to carry the fault current.

 

[L'uomo Universale]

So to be clear, I am talking about the "Neutral" conductor which according to that article is also referred to as "Grounded Conductor Brought to Service Equipment".

According to 250.24 (C)

"The grounded conductor shall not be smaller than specified in Table 250.102(C)(1). Am I correct to size the neutral based upon this table?

If so then I can size the neutral at 12.5% of the "Equivalent Area" of all ungrounded conductors.

 

[david luchini]

So to be clear, I am talking about the "Neutral" conductor which according to that article is also referred to as "Grounded Conductor Brought to Service Equipment".

According to 250.24 (C)

"The grounded conductor shall not be smaller than specified in Table 250.102(C)(1). Am I correct to size the neutral based upon this table?

If so then I can size the neutral at 12.5% of the "Equivalent Area" of all ungrounded conductors.

I would think 250.24(C)(2) would apply to you. Size the neutral in each raceway based per Table 250.102(C)(1) based on the size of the ungrounded conductors in each raceway, but not smaller than #1/0.

 

[L'uomo Universale]

I would think 250.24(C)(2) would apply to you. Size the neutral in each raceway based per Table 250.102(C)(1) based on the size of the ungrounded conductors in each raceway, but not smaller than #1/0.

So by using the table 250.24(C)(2):

If I am showing 12 sets of 400 KCMIL conductors for a 4000A service.

I should size each neutral (one per set) at a 3/0. Would you agree?

I don't mean to press the issue but I am green with the NEC and it can be kind of cryptic at times.

Thanks for all of your feedback!

 

[lauraj]

1/0 should be all you need sized from T250.102(C)(1) going off of the 400kcmil in the conduit.