If the hots come from different circuitsdifferent panels. The 4 way switch is reversing the connection of the hot and neutral travelers and all it takes is for the switch mechanism to momentarily connect traveler to traveler to get a plasma arc.
Managing The Redo Log
Illegal 3 way switch. Because handymen and totally ignorant so called expert electricians refused to stop using it. This was done to save on wire and to avoid having to use 3 wire cables. Conventional 3 way wiring is not very complexwith conventional wiring the line line voltage connects to the common of one switch. Weird and illegal 3 way switch 1. The alternate 3 way switch wiring configuration california or west coast was used as a way to wire 3 way switches and be able to supply line voltage to either switchthis configuration is no longer allowed as the neutral is not present in each switch box. There were also some illegal 3 way set ups done at outbuildings to have 3 way switching of a light and an always live load without having to have a multi wire conduit run.
If the lampholder is screw shell reverse polarity is not allowed. Color of wires to lamp since each is sometimes hot sometimes neutral. I doubt the 4 ways are tested or even designed with this in mind and have to wonder if putting the hot and neutral on travelers isnt a 1103b or nrtl. Because the hot and neutral switch back and forth a 3 way dimmer can not be used the carter circuit was banned in 1923 but i have found them in homes wired all the way up into the 50s and using romex wiring.
Gallery of Illegal 3 Way Switch
