I went to change out an inside panel the other day, and the main panel outside was a "Zinsco" panel. I turned off the
100 amp main that fed the panel I was changing out. Everything went fine. The man also had a dryer that wasn't working. I went to check the voltage at the dryer receptacle, and would get 240 volts one instant, and the next instant there would be nothing. I at first thought my tester was messing up on me, maybe a weak battery etc., but then I remembered the customer's son had checked it earlier and was only getting 120 volts to ground from one phase. I decided to try and find the breaker that controlled it, since it wasn't labeled. I went to the outside Zinsco panel, and started turning off the breakers, waiting for the customer to tell me when it went off. I turned off all the breakers and it still didn't go off. I started to turn them back on, and all of a sudden he yells that is off. So with the breaker in the "on" position it went off, and with
the breaker in the "off" position it was still on. I'm glad I didn't just trust the breaker when I was checking it out. Could have got Zapped pretty good at the least. Even better, I'm glad the 100 amp Zinsco main I had off, while changing the inside panel, didn't go "haywire" the same way.
I might have been a casualty. We've got a lot to be thankful for. Don't ever completly trust the breaker. I'll be thinking a little more of it in the future, especially with Zinsco breakers. Next time I'll probably take the wire off the "main breaker" before I attempt to work it. New things always happening. Never to old to learn. Hope this might help someone else out there. Be careful. Steve...