Voltage on the ground not tripping breaker

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Sierrasparky

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
Was on a unusual troubleshoot today.
I got there and the customer had a couple of switboxes open that someone was working on. The nuetral was melted. I looked at several other boxes and the and the neutral wires were also melted.

Upon inspection at the panel I see the branch circuit tripped for that circuit with the melted wires.
I wiggy the mains. L-L =220 ok,
la-N 120v ok
Lb-N 120v ok
La-ground=120
Lb - Ground NOTHING!!!
Ground to Neutral 120v ----OOPS!!!

I found a recent finish nail shot through the SER cable after opening the wall. The nail went right through the one hot and into the ground. Now what is strange is that there is no shorting, no arcing, just a good connection. I pulled the nail and the problem went away. This is a multi meter unit and there might be a bonding jumper issue at the multi meter wall pack. I have to wait to get the lock rings pulled. Could there be such a High impedence from nuetral to ground.


So the question is why did a circuit neutral melt.
Why did the main 100 amp not open.
Why was there no arcing at the Grounding electrode conductor.




Lb

,
 
With the nail connecting L2 to the EGC no MBJ all of the equipment grounding conductors and surfaces would be at 120V. The grounded neutral would be connected to earth and the POCO neutral. It's Dead Short; just following a different path.

Since there is no overcurrent protection on the grounded conductor you are gonna burn something.
 
FYI As I thought there appeared to be no MBJ at the service. However the nuetral at the service and the feeder to the apt sub was ok. One single branch circuit had a melted nuetral. I have not been able to see where the connection of ground and neutral was tied together at the downstream branch circuit. No appliances were damaged. The TV and cable box were unaffected.
 
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