I need to replace a light switch, which is one of a pair in double switchbox. I discovered that the two switches are on different breakers. Apparently, this is actually to code, but how common is it? It seems like you are asking for trouble when somebody simply assumes that both switches are off when they figure out which breaker goes with the one they want to mess with.
Perfectly common. Don’t make assumptions about what’s live. Get a non-contact voltage detector and use it before sticking your hands in a box.
Just wait until you find a multiwire circuit or get zapped by a neutral that someone tied into and shouldn’t have. That’s fun.
Anyways, that’s why you not only always test, but test all the wires, the hot and the “neutral” and all of the wires that your hands are going to be near. If you want to work on or near live wires, that’s fine, I won’t fault anyone for doing that, just know which wires are hot.
I have some of those NCV detectors. I always tell people, I’ll use them to know when a box has hot wires in it, but I’ll never use it to know when a wire isn’t hot. I just don’t trust them.
That is, I can put one near an outlet and say 'okay, something in here might be live*, but I’d never think to myself ‘it didn’t beep, I can grab this’.
I have 3 or 4 of those cheap neon testers and I keep them around. Far more reliable and cheap enough that I can keep one at work, one at home, one in my car etc.
For the record, I DID check. That’s why I knew. It just struck me as unexpected.
Yes, indeed. They’re a good way to add redundancy, but the potential for a false negative means you should never rely on them alone. Just an additional check that you should add to your arsenal.
Yeah, I picked one up a few years ago (and my multimeter has one built in) to see what they were about. But, I never really did like it that much and I’d certainly never trust it to tell me a circuit is off. But it does have it’s uses.
For example, and this one was interesting. At work I have some outdoor GFCI outlets with some stuff plugged into them. One of the GFCIs was tripped and wouldn’t reset so the question is, is the GFCI broken or is there no power going to it. With a regular probe voltage detector or meter, I’d have to open the box up (and it was overhead, hard to reach and in winter). However, put the NCV detector near it, it beeped, and we can be certain enough that the GFCI outlet is probably faulty that it’s worth picking up a new one before starting on the project.
Yes, there could have been other factors at play, but it was worth it to me to make the run to home depot first instead of having to worry about wires hanging out or putting it back together and then going after verifying that the outlet was getting power.
As for why it was interesting, IIRC I found that even with the GFI tripped (and not resettable), the NCV detector still beeped near the load. That’s one of the way I verified that it was, in fact, the outlet. (Could be misremembering this last part, it was a while ago). So, yeah, I guess it’s another tool to have around, I suppose I won’t toss it just yet.