Picture submitted by Waymag. He'll fill in the details:

Lightning?

We still do not know what made this switch have a melt down. It was on a 277volt circuit and the breaker never tripped. The breaker was a Cutler Hammer Power Line c style breaker. This is also a code violation type deal because 120 and 277 were in the same box. I know the contacts inside the switch had welded together.

The 120V switch and 277V switch can be in the same box IF the voltage between 2 adjacent switches doesn't exceed 300V.

It's in 404.8(B)

(I wonder what the voltage between the 2 systems is?)

Perhaps the switch was not rated for 277?

Best case = 157V, worst case = 397V, depending upon phasing.

My, how simple!

Well it had 120v and basically 480v too because the other 2 switches were 277 on a phase and 277 on b phase... 1-120v switch and 2-277 volt switches...after repullint wire back up to j box I did an amp reading and got 4 amps on the 120v switch 3.5 on one of the 277 volt switches and 1.5 on the other 277 volt switch.