100 Amp main disconnect FRIED!

[Erby]

Any ideas what would cause this, other than a loose connection.

There was a 200 Amp Main panel and this 100 Amp Main Panel, both fed direct from the meter. The only thing the 100 amp panel served was the heat pump.

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[Jim Katen]

Looks like a classic loose connection.

[ghentjr]

If you look at the individual wires you can see that the fried one is not mashed like the clean one. It was time for lunch and they forgot to tighten it.

[LeePlace]

Is that a neutral conductor or a GEC that is blown apart in the bottom right of the panel? If it is a neutral conductor from the heat pump would the higher resistance on the left line created a load imbalance that would have over loaded a down sized neutral? If it is a GEC, a voltage surge?

[Mr. Electric]

The wire marked with white tape is actually a ground, not neutral. Should have been bare or green, but the main issue is the loose connection that failed. Agree with Jim.

[LeePlace]

I was asking about the conductor that is landed at the bottom of the ground buss. The 4 in B4U Close points at it.

[Erby]

Perhaps you can see it better without the water mark.

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[Jim Port]

That looks like the braided ground from the SER cable

[Speedy Petey]

The wire marked with white tape is actually a ground, not neutral. Should have been bare or green, but the main issue is the loose connection that failed. Agree with Jim.

That white IS a neutral. There is a separate ground run to the ground bar.

[Speedy Petey]

That looks like the braided ground from the SER cable

I hate to correct you Jim, but the bare wire in SEU is typically a neutral, and in this case it is connected to the neutral bar.

That bonding jumper is there because this is a main breaker.

[Jim Katen]

I see three service entrance conductors inside conduit coming into the rear of the box - no cable there.

At the bottom of the box, an SE cable runs to the heat pump. The heat pump requires no neutral, so the braid is being used as an equipment grounding conductor.

A jumper runs from the neutral terminal to the accessory grounding terminal bar. The only function of this accessory bar seems to be to accommodate the sideways J-shaped wire that goes to the bonding bushing.

I don't see any grounding electrode conductor, which I would have expected to see.