If there are 2 guys, we generally:
1. Test both of our testers.
2. Each test circuit with our own testers.
3. Each test it with the other guy's tester.
4. Disconnect & cap off the conductors while working.
5. Repeat 1-3 before reconnecting.
(I carry 2 testers in my box, and when alone generally use both).
Although I've changed out lots of fluorescent ballasts hot @ 277 (the only good use for a Wago), that's it! The company I now work for won't allow it. They lost a man about 4 yrs ago working hot 277V.
I wouldn't think of changing a wall switch or a 480 recp hot (You should see what a hot switch to ground will do to a drywall taper's knife!)
[This message has been edited by electure (edited 09-10-2001).]