Yup, Marc's right. (I told the answer on the chat, which may have helped
2 Poles, Hubbell, with a label on the side "2 Pole for single circuit only
The installer chose to disregard the label, and ran 480V through them. The fault was 277V, caused by 8-32 in the corner of a 4-S box. The switch on the left took the fault, and its failure sent this "Jack and the Beanstalk" effect into high gear.
There were 18 of these switches installed (that's 36 circuits). The customer had me remove all of them
They will be replaced with contactors.
(BTW, None of the 20 Amp breakers tripped)
[This message has been edited by electure (edited 11-18-2005).]