Sizing of the Neutral Conductor

[kriverswaters]

If I am planning on installing a Single Phase, 120\240 Volt, 600A Service, to a storage building with 4EA. 200A Single Phase, Sub Panels. Would the NEC Code accept installing 250 MCM AL, for the un-grounded conductors, and a 4\0 AL for the grounded Neutral Conductor to each of the units? The lighting loads are 15KW per unit. What is the "minimum" Neutral size of (Grounded Conductor), that can be used for this application, and where is the "Minimum" size located in the NEC Code Book? 220.61 doesn't seem to make it clear.

 

[Dennis Alwon]

The minimum size grounded conductor cannot be smaller than the calculated load and cannot be smaller than the required equipment grounding conductor.

For a service the neutral or grounded conductor cannot be smaller than the required grounding electrode conductor.

 

[Dennis Alwon]

For Feeders

215.2(A)(2) Grounded Conductor. The size of the feeder circuit
grounded conductor shall not be smaller than that required
by 250.122, except that 250.122(F) shall not apply where
grounded conductors are run in parallel.
Additional minimum sizes shall be as specified in
215.2(A)(2) and (A)(3) under the conditions stipulated.

For Service

250.24(C)(1) Sizing for a Single Raceway. The grounded conductor
shall not be smaller than specified in Table 250.102(C)(1).

 

[Carultch]

The minimum size grounded conductor cannot be smaller than the calculated load and cannot be smaller than the required equipment grounding conductor.

For a service the neutral or grounded conductor cannot be smaller than the required grounding electrode conductor.

How does one know the amount of imbalance among all the line-to-neutral loads, that would govern the amount of current on the neutral?


Good practice is to balance the loads as closely as you can. But there still is the case with the happenstance of what is turned on when, that all the line 1 loads could be off, and only the line 2 loads are on.

 

[don_resqcapt19]

How does one know the amount of imbalance among all the line-to-neutral loads, that would govern the amount of current on the neutral?

Good practice is to balance the loads as closely as you can. But there still is the case with the happenstance of what is turned on when, that all the line 1 loads could be off, and only the line 2 loads are on.

That is exactly how you size it..... that is with all of the 120 volt loads on the leg with the most 120 volt loads on and all of the 120 volt loads on the other leg off.

220.61 Feeder or Service Neutral Load
(A) Basic Calculation. The feeder or service neutral load shall be the ma ximum unbalance of the load determined by this
article. The maximum unbalanced load shall be the maximum net calculated load between the neutral conductor and any one
ungrounded conductor.

Note that often this results in a size smaller than required by the sections that Dennis cited. You must apply the rule that requires the largest conductor.

 

[kriverswaters]

Sizing the neutral

Sizing the neutral

Thanks for your help guys!!! Useful Information!!!