Neutrals burning up in panel

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jumper said:
Charlie's theory is correct, but 1 and 3 are not on the same buss/pole in most panels. Odd is left side and even is right.

1 and 3 are A and B.
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That what was I meant in my post. I guess I should have said bus instead of phase, any way, my point was it is legal-MWBC.

charlie b said:
Mea culpa. I see that now. I should have used circuits 1 and 5 as my example, or perhaps 1 and 2.
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That was what I was trying to point out. 1&3, 3&5, etc. all can be used because they are on different legs/buss/bars.
 
Little Bill said:
That what was I meant in my post. I guess I should have said bus instead of phase, any way, my point was it is legal-MWBC.



That was what I was trying to point out. 1&3, 3&5, etc. all can be used because they are on different legs/buss/bars.
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Bill, we all know what you meant, just as we all know what Charlie meant. Even John is correct as there are panels in which the all the spaces on either side are all on one buss.
 
thanks for the comments I don't remember if the circuits in question were sharing neutrals or not, I'll have to take a few meter readings too. I searched for damage to the neutral bar itself or for a bad incoming connection and couldn't find one. I enjoy this forum you guys make me laugh with your back and forth, I have to admit Charlies first comment did throw me for a loop though. Being from the east coast (Virginia) i've never come across house panels organized in any other fashion than odds on the left, evens on the right, a and b phases alternating vertically. :lol:
 
Just remember when two hots are on different phases then the neutral will see the deferential of the two, I.E one hot has 10 amps, the other hot has 5 amps, the neutral will have the other 5 amp.

But when two hots share the same phase then the two are additive to the neutral, or the neutral will carry the sum of the two circuits, I.E. 10 amp on one hot and 5 amps on the other will put 15 amps on the neutral.

So making sure you have multi-wire circuits on different phases are a must, and it is a very common sign when we see over heated neutrals to check where the hots are landed if it involves a MWBC.

It can be much more of a problem where you have a non-experienced installer that has combined all the neutrals in every junction box, which now you will have a whole house load of over loaded neutrals or the potential to have them.

So the best way is to use an amp meter and start shutting off breakers one at a time and watch to see if it affects the neutral current, but this only works if the circuit has a load on all sides of it.

The most tedious way but effective is to shut off the main and all breakers and using a continuity tester such as a Ideal Vol-Con and remove all the neutrals and then check between all the neutral then from each neutral to each breaker, if it beeps then you know which neutral is going to which breaker, which is when you might find more then two circuits tied to one neutral.
 
neutral burning up

neutral burning up

I am a romex jockey aspiring to one day do more than small commercial remodeling. I have been told that in commercial, it is customary to put three hot wires (from the 3 different phases), (have to be all the same amperage?) on a shared neutral. It doesn't matter if the load is lighting, plugs, motors?
 
difowler1 said:
I am a romex jockey aspiring to one day do more than small commercial remodeling. I have been told that in commercial, it is customary to put three hot wires (from the 3 different phases), (have to be all the same amperage?) on a shared neutral. It doesn't matter if the load is lighting, plugs, motors?
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And the NEC has allowed them for as long as it has existed, and there called a multi-wire branch circuit or (MWBC) for short, but there has been some changes in the past code cycle and it might affect whether or not you would still want to use them, or how you place what loads on them.

Now you must use a single means of disconnect (multi-pole breaker or single pole units with handle ties) to disconnect all ungrounded conductors of a MWBC. 210.4(B) (2008 NEC)

Second you must group them in a way that they can be identified in a panel including the shared neutral. 210.4(D)(2008 NEC)

As for being the same amperage that is a myth, there is no requirement for MWBC being the same amperage just that the common neutral must be sized for the largest circuit used in the MWBC
 
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