Sizing a Neutral for a Sub Panel

[wmeek]

I am wanting to know how you would size a neutral to a sub panel that you are installing for 3phase loads only. I know the code says to run a neutral also, But how do you come up with the correct size. The feeder I am running is a 200A 3phase. I am running 3-3/0 thhn for L1,L2, L3 and a #6 EGC. Any help would be appreciated.

 

[jumper]

I do not think a sub panel requires a neutral, only the main service panel. 250.24(A)

 

[augie47]

............. I know the code says to run a neutral also, ..........................

It does ? where ?

 

[Chamuit]

Do you have any L-N loads?

 

[wmeek]

Sorry I was thinking of the service disconnect where code says you have to run a neutral conductor. Suppose you wanted to run a neutral to a sub panel for future single phase loads what size would you run.

 

[jumper]

Design issue, hard to answer. What is the calculated load on the panel install right now?

 

[wmeek]

The calculated load is 148A . All loads are three phase. Just thinking for future what size could be run.

 

[Dennis Alwon]

The calculated load is 148A . All loads are three phase. Just thinking for future what size could be run.

No neutral is necessary however if you run one then it must be at least as large as the required egc.

 

[wmeek]

So as long as its equal to or larger than a #6 thhn it would be find. this ia far a 200A panel

 

[jumper]

So as long as its equal to or larger than a #6 thhn it would be find. this ia far a 200A panel

It would meet code, as Dennis stated; but will it suffice for all future scenarios? Who knows?

I thought I had a good idea, but it is worthless when I gave it more thought. Sorry.

 

[wmeek]

Probally it would be a good idea to run a 3/0 for the neutral for future ,that way it would be covered most likely.

 

[Dennis Alwon]

Probally it would be a good idea to run a 3/0 for the neutral for future ,that way it would be covered most likely.

If your load on the panel has 148 amps of 3 phase loads why do you think a 3/0 is necessary- you will never have 200 amps on it.

You have 52 amps left on that feeder so I see no reason for 3/0. To your question #6 is all you need

 

[Eric R 1973]

Can"t you use the permitted reductions in Art 220.61 B

 

[jumper]

Can"t you use the permitted reductions in Art 220.61 B

There is no calculated neutral load to reduce conductor size.

 

[augie47]

For a feeder, 215.2(A)(1) provides a guide to the minimum size.

 

[lakee911]

If your load on the panel has 148 amps of 3 phase loads why do you think a 3/0 is necessary- you will never have 200 amps on it.

You have 52 amps left on that feeder so I see no reason for 3/0. To your question #6 is all you need

Maybe he is expecting non-linear loads?

 

[Dennis Alwon]

Maybe he is expecting non-linear loads?

If that was part of the question it could be addressed but even so unless the entire 52 amps were filled with non linear loads it probably would still be okay with a #6 assuming a fairly balanced load. Is that not correct?

I am not sure how you would size for non linear loads on the neutral. Certainly 3/0 is not necessary with the given situation.

 

[Barndog]

If your load on the panel has 148 amps of 3 phase loads why do you think a 3/0 is necessary- you will never have 200 amps on it.

You have 52 amps left on that feeder so I see no reason for 3/0. To your question #6 is all you need

I agree you only have 52 amps left if you max out your panel. so even if you put all your non linear loads on one phase you would only have 52 amps on your neutral. so as Dennis said #6 should be fine.

 

[lakee911]

Ha. Yup. Lol