Originally Posted By: pdacey This post was automatically imported from our archived forum.
Found this in the sub panel today. One of neutrals was scorched and had some corrosion on it. The power to the entire house was off at time of inspection. What would cause this on a single neutral?
Originally Posted By: pdickerson This post was automatically imported from our archived forum.
Probably one of Brian’s suggestions. Also, possibly a faulty circuit breaker in conjunction with excessive current through the circuit. Both this possibility and the overloaded multiwire circuit possibility would not necessarily cause a scorched wire right at the neutral termination. My guess is a loose connection.
Originally Posted By: pabernathy This post was automatically imported from our archived forum.
Also…just in case someone may have overlooked this…do not assume it is just a loose connection…it could also be a multi-wire circuit to which this neutral is carrying a excessive unbalanced load…for example a multi-circuit with one neutral and both HOTS on the same phase…This will cause the neutral to be overloaded and not in balance…thus overheating…
Now days we have to provide a connected tie...but in older units people did a multi-wire circuit and plopped the breakers anywhere...somtimes across from each other making them on the same phase ( or buss bar ) of the panel and the poor neutral had to handle the loads of BOTH hots...
So do not just write it off as a loose connection...this melting is excessive and is coming DOWN the conductor.
-- Paul W. Abernathy- NACHI Certified
Electrical Service Specialists
Licensed Master Electrician
Electrical Contractor
President of NACHI Central Virginia Chapter
NEC Instructor
Moderator @ Doityourself.com
Visit our website- www.electrical-ess.com
Originally Posted By: pdickerson This post was automatically imported from our archived forum.
Paul,
Good comment. If it was an improper Edison circuit, wouldn't you expect to see overheating of the neutral conductor over the full length of the wire instead of focused at the termination? Or is it likely that the termination would have the smallest cross section/contact area and thus be the first to overheat? What are the typical signs of an overloaded neutral in the case of an improper Edison circuit?
Originally Posted By: rcooke This post was automatically imported from our archived forum.
pdickerson wrote:
Paul,
Good comment. If it was an improper Edison circuit, wouldn't you expect to see overheating of the neutral conductor over the full length of the wire instead of focused at the termination? Or is it likely that the termination would have the smallest cross section/contact area and thus be the first to overheat? What are the typical signs of an overloaded neutral in the case of an improper Edison circuit?
The Higher resistance point is where the over heating will show first .
That is where there is a joint or termination .
When heating starts the resistance increases so it will then self feed itself more heat more resistance
Originally Posted By: pabernathy This post was automatically imported from our archived forum.
It is my experience that usually it is a combination of a loose connection and multi-wire neutral overload. The possible theory is it happens from the end where the wire is stripped and higher heat because of lack of insulation near the end that is stripped…then it melts backwards…
But again......no science behind it....
I would simply suggest when an HI is looking at this they should locate the "ungrounded" wires in the circuit with the melted "grounded" wire and see if it is a possible multi-wire circuit.....and then see if they are both on the same side or apart from each other....or on the same side with a breaker between them....either way they are on the same phase and giving an improper balance to the neutral.
The melted insulation is only the starting point....the next point would be to do the following:
1.) Verify the above "ungrounded " ( ie: hot wires ) and see if their are more than (1) coming into the box from the same point the melted neutral enters....
2.) Make sure the " ungrounded" conductor is not one size and placed on a breaker that is oversized....meaning a # 14 AWG on a 30 AMP breaker...trust me...home owners do such a thing....sure it could also melt the black wire insulation as well...but it might not be noticed or started yet.....
3.) Lastly it could very well be a loose neutral....but unless you have a specialty in electrical...I would simply at this point refer it to a licensed electrician....( now I tug on it because I happen to be a electrician so I am comfortable with it....)
But you need to rule out all the above....in determining the problem but in all cases....if questions persist refer to an Electrician.
-- Paul W. Abernathy- NACHI Certified
Electrical Service Specialists
Licensed Master Electrician
Electrical Contractor
President of NACHI Central Virginia Chapter
NEC Instructor
Moderator @ Doityourself.com
Visit our website- www.electrical-ess.com