Cause of Burned Neutrals

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supergeek

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Hello everyone,

Well, I ran across this today and wondered what might be causing it. All the neutrals near the top of the neutral bar are badly burned, yet the bottom neutrals look ok. The main neutral conductor looks clean and the connection is tight. There's hardly any load on the panel - 3 phase 120/208 - because part of the building is being renovated.
I tightened the screws on the neutral wires a little, but they weren't horribly loose. Very little load on the neutral either, under 20 amps when I took the reading. Also, the neutral bar wasn't overly warm, even in the 'problem area' And no signs of water damage or leakage into the panel either. Anyway, thanks in advance for any ideas you might have. The property manager has decided to replace the entire panel, but I don't want it to keep happening.

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I'd be looking at the branch circuit conductors ~ not the neutrals.
It is quite possible someone landed 2 or more legs of a MWBC on the same phase.
 
I see this a lot, particularly in Westinghouse/Bryant style panels. Guys land both conductors of a MWBC on a twin breaker. That sorely overloads the neutral. Your pic is a 3? panel, so I have no idea what's going on there. Looks like somebody got their hots and neutral sets mixed up in a big j-box someplace.
 
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Looking at those pictures ( Last edited by supergeek : Today at 07:21 PM.) ...looks like MWBC is the culprit.

I may be wrong ....but that's never happened before :D
 
Would that affect them all?

Would that affect them all?

So would just one or two overloaded wires cause the adjacent wires to fry also? Or does the heat start a downward spiral of more and more resistance?
 
There is more than 20 amps going through those conductors. I would think that were never tightened. Phasing looks right but can't really tell.

When the screw terminals get that burnt the screw won't turn and may seem tight. I bet someone got distracted and never tightened those screws.
 
IF one or MWBC are on the same phase, it will affect 1 or more neutrals.
It may affect other properly wired MWBCs, but looking at those pictures - to me - it looks like lots of improperly wired MWBCs.


In that first picture....it "looks" like a couple of yellow wires are nutted together...at the nut, one "appears" to be blackened. Are these "yellow" wires also neutrals?
 
celtic said:
In that first picture....it "looks" like a couple of yellow wires are nutted together...at the nut, one "appears" to be blackened. Are these "yellow" wires also neutrals?
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In this case, they are yellow wires attached to a black wire. They went to a timer for the lights - some sort of override if the office folks were working late.
 
hot

hot

I would be curious as to the connection between the neutral bar and the main neutral lug. The bar containing the #12s obviously has been hot...the heat may have generated from the bar connection to the neutral also.
 
augie47 said:
I would be curious as to the connection between the neutral bar and the main neutral lug. The bar containing the #12s obviously has been hot...the heat may have generated from the bar connection to the neutral also.
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One would think that the bottom neutrals would also have a problem. I guess it is possible that the grounded conductors on the bottom have no load on them.
 
It's possible....

It's possible....

augie47 said:
I would be curious as to the connection between the neutral bar and the main neutral lug. The bar containing the #12s obviously has been hot...the heat may have generated from the bar connection to the neutral also.
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I was thinking of that too. There are just 2 screws holding the long neutral bar to an 'L' shaped piece of copper where the main lug bolts on. I wondered if that connection was bad and if that could be the reason all the #12's burned up. When it gets changed out, I'm going to take a good look at that connection and see how tight everything is.
 
neutrals

neutrals

If you think it may have been loose screws check the depth of all of the screws to see that they are all tightened to the same depth with the same size wires. This is one of the first things I look at when I open an unknown panel. could this possibly be from a lightning strike?
 
probably not lightning

probably not lightning

quogueelectric said:
could this possibly be from a lightning strike?
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I'm pretty sure it's not lightning. I'm in Los Angeles and we hardly even get rain! Plus, I haven't seen any other equipment damage that might indicate lightning. Good thought, though.
 
phasing

phasing

supergeek said:
I'm pretty sure it's not lightning. I'm in Los Angeles and we hardly even get rain! Plus, I haven't seen any other equipment damage that might indicate lightning. Good thought, though.
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Did you checkto see if the affected neutrals are tied to any single or two phases in particular as in the case of an open or loose neutral somewhere upstream in the distribution chain such as a main distribution panel or xformer somewhere feeding this animal causing an overvoltage on a particular phase or phases. Do you have a good Idea what the actual loads are on this panel Is it lighting receptacles or both??
 
1. Another thought, if the feeder neutral is not intact and there are downstream grounds on the branch circuit neutrals they could be carrying the neutral current.

2, This may also be from a past problem that has been half corrected, the source of the thermal condition was corrected, but the conductors were not cut back and re-terminated. (I see this a lot).

Reviewing the picture I would put my money on my option 2, there appears to be thermal damage to the bus termination bar, the conductors all at one end, these conductors may have been loose fro the beginning till caught by a previous electrician.
 
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