Down sizing neutral conductor

[cowboyjwc]

I have a contractor that ran 2 #4's with a #10 neutral to a sub panel.

His loads consist of 2 240v 30 amp circuits and one 120v 30 amp circuit.

I believe that per 220.61 he can do this, but I have never seen it in all my years and of course this gives no allowance for future loads.

Any thoughts?

 

[raider1]

Provided that the 240 volt circuits don't also have a neutral load (such as a dryer or range) I believe that the maximum unbalanced load would be 30 amps (or what ever the calculated load of the 120 volt 30 amp circuit is) and the #10 neutral would be OK.

There is no NEC requirement that the panel be sized for a future load.

Chris

 

[augie47]

since he is installing to a subpanel 215.2(A) would apply. Among other things it states: 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.
If he is protecting his #4s at ?60 amp then he would need a grounded conductor larger than #10 per 250.122 & 215(A)(2)

 

[steve66]

If he is protecting his #4s at ?60 amp then he would need a grounded conductor larger than #10 per 250.122 & 215(A)(2)

Never mind.

 

[augie47]

it was a typo Steve, > 60 amps,

 

[Twoskinsoneman]

since he is installing to a subpanel 215.2(A) would apply. Among other things it states: 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.
If he is protecting his #4s at ?60 amp then he would need a grounded conductor larger than #10 per 250.122 & 215(A)(2)

Great call Augie I am wondering what the sub is protected at...

 

[cowboyjwc]

Radier: That's where I was coming from. Thanks.

Augie: He's protecting it with a 60 amp breaker and table 250.122 says that a #10 is good for 60 amps.

I do find it interesting that you go to a grounding table for the grounded conductor, after being taught all these years that they are two different things.

Thanks for the info. 20 years and you can still learn something.:smile:

 

[steve66]

it was a typo Steve, > 60 amps,

I wasn't refering to the typo. Something you posted made me think about overcurrent protection, and I thought your post was refering to the same thing. But then I realized you were talking about something completely different, so I just retracted my entire post.

 

[steve66]

Have you ever though you understood something in the code pretty well, and then something comes along and you realize you don't understand it at all??

Augie's mention of a 60A breaker has me there now.

240.4 says you have to protect wire at it's ampacity. I don't see any exception for neutral wires.

So how can you have anything more than a 30 amp breaker protecting this #10 neutral wire?

Even worse, how can you ever reduce the size of a neutral wire?? 220.61 says we can reduce neutrals, but it doesn't give us any specific permission to ignore 240.4.

I'm confused.

And one more comment: 220.61 says we can reduce service and feeder neutral sizes. But I can't find anything that says we can reduce the neutral for a branch circuit.

 

[Twoskinsoneman]

So how can you have anything more than a 30 amp breaker protecting this #10 neutral wire?

Even worse, how can you ever reduce the size of a neutral wire?? 220.61 says we can reduce neutrals, but it doesn't give us any specific permission to ignore 240.4.

I'm confused.

And one more comment: 220.61 says we can reduce service and feeder neutral sizes. But I can't find anything that says we can reduce the neutral for a branch circuit.

Good question. An EGC only has to carry current for a short while under fault conditions so they are sized smaller because they a very capable of carrying the fault current for that short time.

As far as the neutral it also has to be able to carry fault current. However it is also sized IAW the unbalanced current.

 

[cowboyjwc]

Have you ever though you understood something in the code pretty well, and then something comes along and you realize you don't understand it at all??

Augie's mention of a 60A breaker has me there now.

240.4 says you have to protect wire at it's ampacity. I don't see any exception for neutral wires.

So how can you have anything more than a 30 amp breaker protecting this #10 neutral wire?

Even worse, how can you ever reduce the size of a neutral wire?? 220.61 says we can reduce neutrals, but it doesn't give us any specific permission to ignore 240.4.

I'm confused.

And one more comment: 220.61 says we can reduce service and feeder neutral sizes. But I can't find anything that says we can reduce the neutral for a branch circuit.

It's not a branch circuit, it's the neutral for the feeders to a sub-panel. One of the books I looked at said that the 220v loads do not add anything to the neutral load so since there is only one 110v of 30 amps, the neutral only needs to be sized for that.

As far as knowing the code that's exactly what happened. I've just never seen it before and it actually threw me a little, so the more I read the more confused I got, until I read the Mcgraw-Hill book and then it made sense, I didn't like it any better, but it made sense.

Augie made me look some where that I hadn't looked before and I got the same answer, now of course if his breaker had been a 70 amp, the ungrounded conductors would still have been right, but the neutral would have been too small, but still could have been a #8. If I'm reading that section correctly.

 

[Twoskinsoneman]

You know as much as I HATE to say this I think this rule should be changed to go the way of 310.15(B)(6). Which is to say it should only be allowed on the service due to gauranteed diverse loads.....

That fact is any one could load that panel up with 5 or 6 more line to neutral circuits that ould overload that neutral without ever knowing....

I really hate to dumb down the NEC because of ignorant sparkys but I think it is a rule I would support.

 

[Dennis Alwon]

John, a neutral isn't even necessary if there is no neutral load required in the sub panel. But now that you have a neutral load it cannot be smaller than the egc. We need some of those engineers to explain why because I am sure there is a logical reason.

 

[cowboyjwc]

John, a neutral isn't even necessary if there is no neutral load required in the sub panel. But now that you have a neutral load it cannot be smaller than the egc. We need some of those engineers to explain why because I am sure there is a logical reason.

Twoskins: I agree, sure would be simpler to say the that the grounded conductor shall not be smaller than the ungrounded conductors and then take away all the exceptions.

Dennis: That is correct and if he had done that I would have been fine:smile: like I said, as soon as he did something different it kind of threw me. Also since it was only a 60 amp circuit it only requires a #10 grounding conductor, so they are sized the same.

Thanks again every one and have a great weekend. I'm taking a couple of days off so I'll see you all on Monday.

 

[Dennis Alwon]

Don't go yet. What about 250.122(B). Problems there I see.

 

[Twoskinsoneman]

Don't go yet. What about 250.122(B). Problems there I see.

God I hate that rule....

are the wires increased in size??

Where the ungrounded conductors are increased in size.....

That sentence need revising....

I guess you could interpret it as increased more than the minimum required for the calculated load... Don't know how else to interpret it... I guess your right the #10 would be no-go

 

[cowboyjwc]

Don't go yet. What about 250.122(B). Problems there I see.

The thing I see is that you have other code sections that counterdict that.

I may have to bring this up at my next IAEI meeting and see what they have to say.

 

[dbuckley]

240.4 says you have to protect wire at it's ampacity. I don't see any exception for neutral wires.

So how can you have anything more than a 30 amp breaker protecting this #10 neutral wire?

The neutral wire is protected by a 30A breaker, which is the breaker that feeds the only circuit that the neutral wire is connected to. So its acceptable and safe. Just. The neutral wire only needs to be protected against overload, not short.

In my opinion in a situation like this there should mandatorially be a warning label permanently attached to the panel indicating that the total 120V load cannot exceed 30A, to stop a future electrician from making a bad assumption and subsequently overloading the neutral.

 

[benaround]

Actually, as long as loads with a total of less than 30a were put on the phase opposite

of the original, it would still balance out.

 

[cowboyjwc]

The neutral wire is protected by a 30A breaker, which is the breaker that feeds the only circuit that the neutral wire is connected to. So its acceptable and safe. Just. The neutral wire only needs to be protected against overload, not short.

In my opinion in a situation like this there should mandatorially be a warning label permanently attached to the panel indicating that the total 120V load cannot exceed 30A, to stop a future electrician from making a bad assumption and subsequently overloading the neutral.

Actually That's a pretty good idea.:smile:

Well I brought it up at my meeting and they all agreed that it complied. One guy complained and said what about if they try to add new loads to it? I told him that I had learned the "you can't inspect what they might do." (I heard that here)