Heat marks at bond screw in sub panel

This is a townhome built in 2005. All the services to the townhomes are at the street and run underground to the units. It is a 3 wire feed so my understanding is the bond screw in the sub panel is correctly installed. Question is why would there be what appears to be arcing at the bond screw? This was the only spot in the panel I saw any heat damage. I am not asking so I can include anything in the report. Just would like to know why this happened.

You gave us no where near enough info to make any kind of determination.
I cannot see any " arcing at the bond screw " from your images…Nope!
I’m not sure if the screw should be there in the first place.
It looks like from your images it is alone on that busbar.

1 Like

Greg, the way I see it from the photo’s is a main service disconnect below the meter and a sub-panel in the condo. If that is correct the bond screw should not be there.
As for why it is shows ‘heat damage’, I have no idea.
Also, are all those tandem breakers in the lower half ok per panel label. Their physical profile is visibly different than the Square D breakers.

So being a 3 wire feed the bond screw should be removed? yes they are tandem breakers.
What other information are you looking for Roy?

Is there any others conductors on the bonded busbar? I only see a portion of the bar.
See image.

I would think that being a sub-panel it should have had a 4-wire feed and the neutral and ground busses isolated.


The ground is provided via the metal conduit… the sub-panel in the picture should have its neutral separated from the cabinet. If someone tried to bond it while in service it would arc because you just connected another path for current to travel on back to the service panel.


I agree with Simon…

The conduit is PVC

No other ground path?

Do you have a pic of the whole panel inside with the cover off?

Not back to the service unless I missed something. There is a ground rod for the sub panel and at the service. And no good picture of the complete sub panel

What is this wire?

To the ground rod

It looks like it is not connected to anything at the right arrow.

It is just looped around. It is connected to the ground buss bar

Looks like the ground screw is loose, are there any neutrals connected to the EGC bus? If so the neutral current is flowing through the loose ground screw. Since this is pre-2008 NEC a 3 wire feeder is permitted.

1 Like

I cant positively answer that question because I have no pictures to confirm but Im fairly certain all the neutrals were on the neutral bus bar. So the bond screw being installed is correct since it is a 3 wire feed with PVC conduit?

The only grounding electrode was a rod? If there was a water pipe then I could see some of the neutral current returning on the GEC through that screw.

Yes only 1 ground rod and the water lines are cpvc. The gas piping was not bonded

This house is in the city so it had to pass their inspections when built.