Burnt bonding screw

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Peter Furrow

Peter Furrow

We’re not born humble, we’re born to be humbled
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Electrical contractor
Notice the bonding screw is burnt. My guess is that there is objectionable current on the circuit grounding conductors that is attached to the grounding bar to the cabinet casing. The bonding screw is probably loose which caused the arcing around the bonding screw.
I’m reviewing the home inspection report and will have to visit the property today.
 

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Lightning or a fault current at one time or another. Neither of which is objectionable current If this were the SE.

The issue would be that this appears to be a feeder where the grounded conductor is improperly bonded a second time.

Simply removing the screw should be all you need to do.
Don‘t count on it.

eta: I now see the EG bars. Changed my answer
 
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If you read that little sticker above the bonding screw it says to torque the screw BEFORE mounting the panel. That's so the screw can go all the way in without the wall preventing it from being tight. That could have been part of the problem, but probably was a fault at some time as well.

ETA: It appears the box is recessed and there is probably room behind the box so the screw probably didn't hit the wall.
 
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Looks to me like there is no jumper between left neutral bar and right neutral bar. That panel series usually has the bar running across the bottom of the interior assembly between the two bars, I see nothing there. Neutral current for left bar was likely finding a path through some EGC, maybe other equipment and then back to the right possibly via the bonding screw.


Add: never mind I now see a bonding jumper between bars that is on top of the breakers.
 
I assume you checked the bonding screw to make sure it was tight. Tight up against the neutral bar tab. It may just be barely touching the tab making a poor contact. In the event of a bolted ground fault it couldn't handle the high current back to the service neutral conductor.

Install a couple of bonding jumpers from the neutral bar to each equipment ground bar.
 
kwired said:
Looks to me like there is no jumper between left neutral bar and right neutral bar. That panel series usually has the bar running across the bottom of the interior assembly between the two bars, I see nothing there. Neutral current for left bar was likely finding a path through some EGC, maybe other equipment and then back to the right possibly via the bonding screw.


Add: never mind I now see a bonding jumper between bars that is on top of the breakers.
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Yes,but you're right. I've seen that type be loose from the factory. More than once.
 
It's hard to tell from the photo but the bonding jumper appears like the insulation has a dull surface and may have overheated. The jumper also looks somewhat inadequate in gauge but again hard to tell.
 
synchro said:
It's hard to tell from the photo but the bonding jumper appears like the insulation has a dull surface and may have overheated. The jumper also looks somewhat inadequate in gauge but again hard to tell.
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Pretty sure it has a insulating covering on it, mostly because of close proximity to the ungrounded lugs/buses.
 
synchro said:
It's hard to tell from the photo but the bonding jumper appears like the insulation has a dull surface and may have overheated. The jumper also looks somewhat inadequate in gauge but again hard to tell.
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That wouldn't cause the burn mark around the grounded conductor neutral bar tab bonding screw.
 
I don't know how old the installation is, or the history, but the large number of wire nuts suggests to me that this might indeed be the service equipment, installed by a hack replacing a split-bus panel. Peter, I'd dig a little deeper before trying to fix the unfixable (at a reasonable price).

In relatively recent days, it is certainly not compliant, being either a service equipment with more than 6 breakers required to isolate, or a "subpanel" without EGC. If a subpanel, the use of L-N-L 230V circuits from a panel with uninsulated "neutral?" has been against code a long time, although not uncommon.
 
oldsparky52 said:
I thought I saw one on the left ground bar near the middle of that bar.
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Yeah, I saw that too. It looks like it goes out the top left side of the panel. Why wouldn't it be landed on the neutral bar? On the right side neutral bar. And if it's the service panel why waste money on two EG bars? Plenty of room on the neutral bars for the EGCs. Unless the panel was originally wired as a subpanel.

The OP needs to supply more info. Is there another panel or a separate main disconnect enclosure where the grounded conductor is bonded?
 
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