"Eeyore" wrote in message
...

Chris wrote:

I've got a ~2 year old microwave that has shown no previous signs
of trouble and is to all appearances in good working order. During
normal operation (melting butter on low power)...

That isn't a suitable load for a microwave, is it? You need some water
in there. No surprise it arced.

I don't think that's correct. Butter contains water and fat, both of which
absorb microwaves. I've melted butter without problems.

Arcing usually occurs at a sharp metal edge. I once put a plastic jar of
Adams peanut butter in my microwave to soften it up, and got serious arcing
on the teensy bits of aluminum foil that had been left behind when I peeled
off the inner seal.