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-   -   Singed Neutral (http://www.diychatroom.com/f18/singed-neutral-26092/)

capt2 09-01-2008 12:21 PM

Singed Neutral
 
I noticed inside my panel that one of the 12ga neutrals was a little burnt near its screw at neutral bus. I tried to remove it but couldn't turn the screw--it was locked up. Finally I cut it and re-terminated it under another screw.
--Could this this have been caused by the screw being loose?? (I can't tell since it was locked?)
--What else may have caused this? How much of a concern is it? (I've never blown any fuses)
Thanks in advance.

220/221 09-01-2008 02:26 PM

Quote:

Could this this have been caused by the screw being loose??
Possibly. It could have also been cause by an overloaded circuit.

Are there any red wires attached to any breakers?

It is not uncommon to have multi circuit branch circuits in houses. A 3 wire cable is run from the panel to a junction somewhere inside where it splits off into 2 circuits. In this installation the two circuits "share" the neutral.
This works fine if the two circuits are on opposite "phases" but if they are on the same "phase" the neutral will be carrying twice the load it was intended for.

If you have red wires in your panel, make sure that the black, in the same cable is on the opposite "phase" or leg.

The phases alternate top to bottom A, B, A, B etc.



Burned neutrals...not a very clear pic but several are burned/discolored.
http://i8.photobucket.com/albums/a8/...2/DSC01743.jpg

SD515 09-01-2008 02:35 PM

In addition to what 220/221 said:
12 ga is good for 20 amps. Is the panel fused or have breakers?? 'Over-fusing' a circuit can melt/burn wires, but yours sounds like it could have been loose, and now the screw is probably welded from the heat.
FYI...neutral wire terminations can only have one wire under a screw.

Termite 09-01-2008 04:17 PM

I'm with 220/221...
This just smells like an overloaded neutral from an improperly phased multiwire branch circuit. If the lug were loose I'd find the burnt area easier to attribute to a bad connection...But it wasn't loose.

Capt2, if you aren't 100% confident in your electrical abilities, please call an electrician. If the neutral is cooking in the panel, it could be cooking somewhere else in your house just as easily. This is the sort of thing that will burn a house down before a breaker trips.

wire_twister 09-01-2008 04:18 PM

sd515 that is not always the case. I install alot of Cutler Hammer load centers, and the instructions inside the door state the neutral bus terminals are good for up to 3 awg 12 wires, but they must be the same size and material.

jerryh3 09-01-2008 04:24 PM

Quote:

Originally Posted by wire_twister (Post 153929)
sd515 that is not always the case. I install alot of Cutler Hammer load centers, and the instructions inside the door state the neutral bus terminals are good for up to 3 awg 12 wires, but they must be the same size and material.

Isn't that only when they are grounds? Doesn't the NEC allow only one grounded(neutral) wire in each screw terminal?

Matsukaze 09-01-2008 05:14 PM

Quote:

Originally Posted by jerryh3 (Post 153932)
... Doesn't the NEC allow only one grounded(neutral) wire in each screw terminal?

That's correct. Article 408.41 prohibits terminating another wire in the same terminal as a grounded (neutral) conductor. There is an exception for parallel grounded conductors if the terminal is identified for more than one wire.

jrclen 09-01-2008 05:45 PM

In my experience when a wire is subjected to overload, the insulation is discolored over it's length. When the discoloration is only a small section next to the terminal, it has been caused by a loose connection. A terminal screw bound up from the heat confirms the loose connection theory for me.

Take another look at it in a few weeks or months.

theatretch85 09-01-2008 06:52 PM

I would agree with jrclen. I created a thread on here a few weeks ago regarding a melted service entrance wire in a main panel, where the last 4 inches or so were melted and charred, and attempting to tighten the lug down on the loose wire it was stuck in place (seized from the heat buildup).

Loose connections are no good, when the wire doesn't make a solid connection it builds up heat as the electricity is trying to make the connection, the more current you try pulling through that loose connection the worse it gets. Just be glad that loose neutral was on a branch circuit and not the main breaker! in the instance I saw the charred wire entering the main breaker, the whole panel needed to be replace and cost about 4,000 to do so.

capt2 09-01-2008 07:06 PM

Thanks for the replies. There is no red wire or multi-wire circuit involved. And it IS just burned near the bus only. A loose screw sounds like the best news if that is the case. And yes I will re-check the wire near the new screw that I re-terminated it to--in a few weeks. THANKS again.

SD515 09-01-2008 07:57 PM

Quote:

Originally Posted by wire_twister (Post 153929)
sd515 that is not always the case. I install alot of Cutler Hammer load centers, and the instructions inside the door state the neutral bus terminals are good for up to 3 awg 12 wires, but they must be the same size and material.

Twister...next time you get a chance, would you double check that label. I would be curious to know if those LC's actually state 'neutral/grounded' wire or 'grounding' wire can be up to 3. As Matsukaze stated, I know 408.41 prohibits 'grounded', but they do not prohibit 'grounding' (bonding).

Quote:

Originally Posted by SD515 (Post 153909)
...sounds like it could have been loose, and now the screw is probably welded from the heat.

Quote:

Originally Posted by jrclen (Post 153953)
...A terminal screw bound up from the heat confirms the loose connection theory for me.

Same principle an arc welder works on. A loose connection creates a gap for an arc...the arcing welds the screw.

wire_twister 09-01-2008 09:00 PM

The label states the same for both the grounded, and grounding bus bars.

jrclen 09-02-2008 08:43 AM

Quote:

Originally Posted by wire_twister (Post 154048)
The label states the same for both the grounded, and grounding bus bars.

NEC 408.41 Each grounded conductor shall terminate within the panelboard in an individual terminal that is not also used for another conductor.

Exception: Grounded conductors of circuits with parrallel conductors shall be permitted to terminate in a single terminal if the terminal is identified for connection of more than one conductor.

The NEC overrides the label on the panel for grounded (white wire) conductors on the bus. Grounding conductors are allowed to comply with the label.

408.41 was put in the code in the 2002 cycle. Prior to that the panel label or listing usually stated one grounded conductor per terminal.


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