Michael writes: I got a call from a colleague to come check out a panel, and here is what I found.

This panel was a 3-phase 225A main. The cause for the fire is still up in the air. The electrical system in the plant in which this panel was located is “dirty” to begin with; every ground point of the raceway (screws, straps, locknuts) had black arc spots.

After the fire, the coils of the transformer were expanded to double their normal size. The ground wire was traced from the Xo point to the point of the grounding means, which was a water pipe. Sure enough, the water pipe had been cut on both sides of the point of connection.

(Courtesy Michael Kelly of The Electrical Department Co.)

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