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Why all the scorched neutrals?


inspectorreuben
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Perhaps only one or a few of the scorched connections generated the heat and the conducted heat ended up being sufficient to burn the insulation of other nearby conductors.

Heat in small quantities does worsen some types of connections and lead to additional heat being developed.

As to which connection began developing heat...look at the screws. There's one that sticks out. Third from the bottom. Look like it severed and left a piece of conductor.

Marc

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Perhaps only one or a few of the scorched connections generated the heat and the conducted heat ended up being sufficient to burn the insulation of other nearby conductors.

Heat in small quantities does worsen some types of connections and lead to additional heat being developed.

As to which connection began developing heat...look at the screws. There's one that sticks out. Third from the bottom. Look like it severed and left a piece of conductor.

Marc

I see the screw you're talking about. It seems unlikely that one scorched wire could have caused all of those other wires to get scorched like that though, doesn't it?

- Reuben

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I've only found one scorched conductor at a time. Multiple ones is kinda weird.

Agreed. I've never seen a bunch like that before either.

Electrician with a limp wrist.

Maybe I should have tried tightening a few of the screws to see if they were loose? I wanted to pull on a few of the wires, but the panel was just too messy to go sticking my hands in there.

You also have ground wires on the neutral bus bar ...

I see a bonding strap on that bar so, presumably, it is service equipment and therefore no harm having grounds and neutrals on the same bar.

Correct.

- Reuben

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The neutral bus grounding strap has also been hot, and it is right next to that burnt neutral. There could have been a massive power surge on a neutral. I wondered about lightning as well, or a high tension lead striking the service drop. Maybe a transformer blew. If a surge hit the neutral service, it could have taken the grounding strap back to ground.

I wouldn't have messed with it at all. Best to let the electrician see the panel in it's unaltered state.

Good catch, Reuben.

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The uniform discoloration of the neutral bar might suggest that the neutral bar was the source of the heat. If so, my vote would be for lightning. It may have heated through energy traveling through the ground conductors. The corrosion on the connections could have happened after the affects of lightning.

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I wondered about the "all screws loose" scenario too. In Reuben's photo, it looks like the screw heads are recessed to the level they would be if they were tightened. The ones in your photo don't look the same.

Douglas Hansen

Though I rarely use a flashlight when taking pictures, I used one here just to highlight the height of the screws. Reuben used the flash on his camera, which tends to flatten the image.

Still, I see what you mean. If those screws are loose, they're not loose by much.

If it was from a lightning strike, it would had to have been just right - enough to burn the higher-resistance connections, but not high enough to burn the wires themselves. I'd also expect to find similar burning at other connections elsewhere in the system.

- Jim Katen, Oregon

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I wondered about the "all screws loose" scenario too. In Reuben's photo, it looks like the screw heads are recessed to the level they would be if they were tightened. The ones in your photo don't look the same.

Douglas Hansen

Though I rarely use a flashlight when taking pictures, I used one here just to highlight the height of the screws. Reuben used the flash on his camera, which tends to flatten the image.

Still, I see what you mean. If those screws are loose, they're not loose by much.

If it was from a lightning strike, it would had to have been just right - enough to burn the higher-resistance connections, but not high enough to burn the wires themselves. I'd also expect to find similar burning at other connections elsewhere in the system.

- Jim Katen, Oregon

In Reuben's photo, there are indications of overheating on the equipment grounds and the bonding jumper, perhaps a point for the lightning scenario.

There is also a lot of corroded copper, something I wouldn't anticipate from a one-time event, and that would more likely be associated with some long term overheating. Take back that point from the lightning side of the scorecard.

It would be interesting to know the history.

Douglas Hansen

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Perhaps only one or a few of the scorched connections generated the heat and the conducted heat ended up being sufficient to burn the insulation of other nearby conductors.

Heat in small quantities does worsen some types of connections and lead to additional heat being developed.

As to which connection began developing heat...look at the screws. There's one that sticks out. Third from the bottom. Look like it severed and left a piece of conductor.

Marc

I see the screw you're talking about. It seems unlikely that one scorched wire could have caused all of those other wires to get scorched like that though, doesn't it?

- Reuben

The breaker will never trip, as long as volts & amps are within its limits. If volts are low, and amps are high, the breaker will only trip if if overheats to the point that it exceeds the setpoint that it was engineered for.
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Perhaps only one or a few of the scorched connections generated the heat and the conducted heat ended up being sufficient to burn the insulation of other nearby conductors.

Heat in small quantities does worsen some types of connections and lead to additional heat being developed.

As to which connection began developing heat...look at the screws. There's one that sticks out. Third from the bottom. Look like it severed and left a piece of conductor.

Marc

I see the screw you're talking about. It seems unlikely that one scorched wire could have caused all of those other wires to get scorched like that though, doesn't it?

- Reuben

The breaker will never trip, as long as volts & amps are within its limits. If volts are low, and amps are high, the breaker will only trip if if overheats to the point that it exceeds the setpoint that it was engineered for.

A thermal/magnetic breaker will trip much sooner than normal if it receives additional heat from an external source such as a bad connection at the terminal or bus bar.

Marc

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