Multi wire circuits

[Brandon Loyd]

Having a 3 pole, 20 amp breaker, is it legal to install #12 on two poles and #10 on the other?

 

[jumper]

Yes. The EGC for the MWBC would need to be a #10. 250.122(B)

 

[charlie b]

Yes. But if the circuits share a common neutral, then it has to be #10. Also, if they share a common EGC, it also has to be #10.

Now that I have typed that, I am suddenly uncertain about the sentence that starts with "but if." I don't want to withdraw it, but I am not sure the code would back up my claim. What do you all think: Can you have a #10 ungrounded and a #12 grounded on a 20 amp circuit? :?

 

[jumper]

Yes. But if the circuits share a common neutral, then it has to be #10. Also, if they share a common EGC, it also has to be #10.

Now that I have typed that, I am suddenly uncertain about the sentence that starts with "but if." I don't want to withdraw it, but I am not sure the code would back up my claim. What do you all think: Can you have a #10 ungrounded and a #12 grounded on a 20 amp circuit? :?

I cannot find a reference but I really want to say no. Somewhere I am hoping that there is something like 215.2(A)(2) for a branch circuit and then I can apply 250.122(B) to the grounded conductor.

(2) Grounded Conductor. The size of the feeder circuit
grounded conductor shall not be smaller than that required
by 250.122.....

 

[infinity]

Yes. But if the circuits share a common neutral, then it has to be #10. Also, if they share a common EGC, it also has to be #10.

Now that I have typed that, I am suddenly uncertain about the sentence that starts with "but if." I don't want to withdraw it, but I am not sure the code would back up my claim. What do you all think: Can you have a #10 ungrounded and a #12 grounded on a 20 amp circuit? :?

Since this is a 20 amp circuit I see no reason why you would need a #10 neutral. I agree with you on the EGC.

 

[Howard Burger]

larger neutral for harmonic on 3 ph non-linear

larger neutral for harmonic on 3 ph non-linear

Wouldn't running a larger neutral on three-phase non-linear loads allow for the increased return on the shared neutral? Worked for a company once where that was the policy for lighting loads; then the economiy got tight and they went back to running all the same size...

 

[Barndog]

Since this is a 20 amp circuit I see no reason why you would need a #10 neutral. I agree with you on the EGC.

The neutral must be a 10 as well. If you increased for voltage drop they must increase as well and also isn't the neutral required to be at least the size of the ground wire?? making it a 10 also.

 

[infinity]

The neutral must be a 10 as well. If you increased for voltage drop they must increase as well and also isn't the neutral required to be at least the size of the ground wire?? making it a 10 also.

I see the logic but can you cite a code section that makes this a requirement?

 

[Little Bill]

Having a 3 pole, 20 amp breaker, is it legal to install #12 on two poles and #10 on the other?

To the OP:
Now that this has been discussed some, please tell us your application for this. It might aid in the answer. IE., is the #10 for voltage drop?

 

[jumper]

I see the logic but can you cite a code section that makes this a requirement?

Nope, and it is driving me nuts.:rant::rant::rant:

 

[hurk27]

Having a 3 pole, 20 amp breaker, is it legal to install #12 on two poles and #10 on the other?

Yes. But if the circuits share a common neutral, then it has to be #10. Also, if they share a common EGC, it also has to be #10.

Now that I have typed that, I am suddenly uncertain about the sentence that starts with "but if." I don't want to withdraw it, but I am not sure the code would back up my claim. What do you all think: Can you have a #10 ungrounded and a #12 grounded on a 20 amp circuit? :?

I think you guys are reading too fast

this has nothing to do about the neutral or EGC, and he doesn't mention that the #10 was ran for voltage drop, it might have just been what was already installed and wants to use it? I don't see anything in the NEC that would prevent him from using two #12 phase conductors and a #10 phase conductor to feed the hots to a MWBC circuit.

Sure now if this #10 was run for voltage drop then that is another issue if not run in a metal raceway.

 

[hurk27]

I guess I have a question:
If I have a circuit that is just a little over the 5% voltage drop and just up sizing the hot would bring it back down is there a code that would prevent me from only up sizing the hot and not the neutral?

 

[hurk27]

I cannot find a reference but I really want to say no. Somewhere I am hoping that there is something like 215.2(A)(2) for a branch circuit and then I can apply 250.122(B) to the grounded conductor.

(2) Grounded Conductor. The size of the feeder circuit
grounded conductor shall not be smaller than that required
by 250.122.....

Wow using a requirement for the EGC for a neutral then using a rule for a feeder for a branch circuit?

talk about mixing apples and oranges:lol:

 

[jumper]

Wow using a requirement for the EGC for a neutral then using a rule for a feeder for a branch circuit?

talk about mixing apples and oranges:lol:

Alright, I admit I am toast. I had to throw whatever I could out there.

I am taking my ball and going home.

 

[hurk27]

Alright, I admit I am toast. I had to throw whatever I could out there.

I am taking my ball and going home.

Sorry I wasn't meaning as bad as I don't think I have an answer either, I'm not up to date on some of these newer changes and barely have been getting the 208 digested which we just changed to. looks like it will be awhile till we are on the 2011.

I do the same thing, through out what I think and hope someone will show me what is correct.

 

[jumper]

Sorry I wasn't meaning as bad as I don't think I have an answer either, I'm not up to date on some of these newer changes and barely have been getting the 208 digested which we just changed to. looks like it will be awhile till we are on the 2011.

I do the same thing, through out what I think and hope someone will show me what is correct.

No need to say sorry, if you go back I had already admitted I could not refute the argument. I searched for 30 minutes and got zip. I would not mix the sizes on this application, but darn if I can find a reference that says you cannot.

 

[Dennis Alwon]

As far as I know you can but there is nothing that I could find to support that for branch circuits other than ranges, dryers, etc. I believe we had a long discussion on this and art. 210.19. If I recall I wrote a proposal for this to be clarified. BTW, proposal deadline is coming quickly, I believe Nov.4, 2011

 

[Barndog]

I see the logic but can you cite a code section that makes this a requirement?

no i can not. i thought i read both of them here on this forum.

 

[Brandon Loyd]

To the OP:
Now that this has been discussed some, please tell us your application for this. It might aid in the answer. IE., is the #10 for voltage drop?

The problem is that I don't know what the application is. We are performing preventative maintenance inspections while also reporting any code violations/installaion errors. One of our guys found a 3 pole 20 amp breaker with 2-#12 and 1-#10 leaving a BCP. He sited this as being a code violation, but couldn't back it up. I am trying to validate this as a code violation even though I don't believe it to be one. I think it is more than likely they just pulled in a #10 because that is the wire they had available.

 

[dana1028]

I guess I have a question:
If I have a circuit that is just a little over the 5% voltage drop and just up sizing the hot would bring it back down is there a code that would prevent me from only up sizing the hot and not the neutral?

2 responses -
- There is no code requirement to upsize the hot for VD, therefore, no code to require the neutral.
- The formula for VD includes the neutral path, so by not upsizing the neutral would impact the over all VD calc [assuming a 2-wire circuit].