Pic of melted lug

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electricmanscott

Senior Member
Location
Boston, MA
Check out this lug. It was pointed out by a home inspector. My feeling is that there is no heat issue here. The panel is part of a 400 amp service installed in the early 70's. Pretty unusual for a dwelling of that era. The owner is a commercial construction guru and his buddies "found" the panels on a job.

Anyway, it looks to me like an Allen wrench was probably blown to bits by some poor guy. There is no evidence of overheating on the wire or lug itself.


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Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Looks like your old work is coming back to haunt you. :grin:

Am I seeing that the lug was beaten to pieces? Was that before or did you do that trying to get the lug loose.
 

chris kennedy

Senior Member
Location
Miami Fla.
Occupation
60 yr old tool twisting electrician
Notice that the damaged lug has twice as many threads exposed and the conductor isn't as compressed as that on the left. Can you say torque wrench?
 

mcclary's electrical

Senior Member
Location
VA
The only way I can see that happening is someone stuck an allen wrench in it while it was energized, then rotated wrench against side of pan. Kaboom
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Well I guess that answers a lot of questions. Obviously the installer got a bad thread or cross thread and tried to beat the lug tight. It obviously didn't work very well. :)
 

electricmanscott

Senior Member
Location
Boston, MA
Well I guess that answers a lot of questions. Obviously the installer got a bad thread or cross thread and tried to beat the lug tight. It obviously didn't work very well. :)

I don't think so. The lug isn't really beat up. The set screw is melted, but only the center area. I think somebody was torquing live and had themselves a little 4th of July!
 

kwired

Electron manager
Location
NE Nebraska
If an arcing incident is there any sign of the other end of the short circuit. An energized wrench in free air should not arc.
 

benaround

Senior Member
Location
Arizona
I would bet it stripped out the inside of the allen bolt and made that little mark on the

neutral lug that is sticking out, just a guess.
 

Jim W in Tampa

Senior Member
Location
Tampa Florida
Safe to say that it had a short threw an allen wrinch. That in itself does not concern me. What i would be concerned about is if it is tight. If you can torque it fine. Why not simply replace it.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
If an arcing incident is there any sign of the other end of the short circuit. An energized wrench in free air should not arc.

I was wondering that also. One would think the side of the can would have matching marks.
 

e57

Senior Member
Yeah - this thing should have a matching arc somewhere - but maybe not???

As far as it surviving it - load that phase up. Take some temp measurements before, during and after, along with ambient.
 

A-1Sparky

Senior Member
Location
Vermont
Safe to say that it had a short threw an allen wrinch. That in itself does not concern me. What i would be concerned about is if it is tight. If you can torque it fine. Why not simply replace it.

I agree. Why take any chances with this? Just de-energize and replace the set-screw and/or lug. You can then torque to specs and never worry about it again.
 
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