William Sommerwerck wrote:

"Eeyore" wrote
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.

Maybe the quantity wasn't enough ?

Graham