Ground and hot wires touched-safe?

October 4, 2009 12:46 PM

[Electricity Filter]: Ground wire touched hot wire and singed the contact point; are we safe to use the appliance?

We installed a new, very basic, range hood. We attached the hood to the underside of the cabinets just fine. When attaching the wires, the ground accidentally touched the hot wire-it made a zapping sound, flipped the breaker, and singed the contact point for the wire on the range hood. We connected it up and it all works fine. Are we safe to just use this range hood? Should we buy another one? We are a bit skittish about electrical matters; should we have an electrician look at it? (which seems a bit excessive for a $30 range hood, but we don't want a fire.....)

posted by Mrs. Green to home & garden (9 comments total)

It sounds like you were attaching the leads while the circuit breaker was on. Please please please never do that again. ALWAYS turn the main power off while wiring up appliances. Messing around with live wires is incredibly unsafe if you don't know what you're doing.

That said, the range hood is probably fine. But if you don't know much about electrical stuff, you might want to call an electrician, or at least a knowledgeable friend -- more to double-check the connections than to inspect the hood itself.
posted by Commander Rachek at 12:58 PM on October 4 [1 favorite]

I am not an electrician, but it would seem that if you hooked it up correctly and the hood still works, and your breaker still works as a safety net, you're good. You made a mistake, and the breaker tripped. That's what they're for, no biggie.
posted by deadmessenger at 12:59 PM on October 4

Oh, and ditto what Commander Rachek said about safety. I debated whether to put something like that in my comment, because it was kind of ambiguous as to whether you were working on a live circuit, or whether the breaker flipped once you turned it back on after hooking it up incorrectly. If the former, yeah, you dodged a bullet, and let that be a learning experience for you.
posted by deadmessenger at 1:01 PM on October 4

When attaching wires, it is best that the copper surfaces are completely clean. This is because the residue can cause interruption of the current flow, which can lead to arching, which then leads to more residue and even more arching.

If this situation was in the open, it could fairly easily lead to fire. If it is contained in a metal box, like an outlet box or a range hood or whatever, it is only a minor safety issue (fire could still get out of the box, it is just very unlikely). However, it is still a reliability issue. Eventually, enough residue could build up that the device simple never turns on anymore.

Don't overreact to all that though.. It really depends on how much area was 'singed'. If it was a tiny fraction of the area, less than 10%, you've nothing to worry about. If it was more than half the area, you should really open it up again and clean off the carbon residue.

Why did you work on these wires with the breaker on? Personally, even turning the breaker off isn't enough to satisfy me. I keep a non-contact voltage detector around to confirm that there is no voltage present. I'll even sometimes careful touch hot to ground just for the satisfaction of seeing no spark :)
posted by Chuckles at 2:26 PM on October 4

Thanks for all your responses-

Clarification: the breaker was off when we hooked it up. Breaker switched back on and we verified that it worked. Went to put the cover over the wires and noticed that the ground was sticking out at an angle which would prevent the cover from going on. Moved the ground so we could get the cover on, but it touched (it had a long section of exposed metal) the copper connector part (the part connecting the appliance wires to the appliance) causing the zap, the breaker to flip, etc.

I will double check the amount of area singed, but it wasn't much. These answers are really helpful-
posted by Mrs. Green at 2:55 PM on October 4

If you're worried, you can replace the breaker with an arc-fault interrupter breaker. It's supposed to prevent chuckle's scenario.
posted by malp at 4:34 PM on October 4

It really depends on where the zap was. Your first description ("contact point") made it sound like one of two mating surfaces (eg, a plug prong, or the very end of a wire) was scorched. If that's true, and current has to flow through the scorch to get from one wire into another, then you should at least clean the scorch with steel wool until you see nice bright shiny copper instead of copper oxide + miscellaneous crap.

However, your second description sounds much more like you zapped the side of a wire inside the box -- that, in other words, you don't have to make an electrical connection directly to the point that was scorched. If that's the case, assuming the zap only scorched (and didn't cause any pitting) then you should be fine.

One more thing -- you mention there being a lot of exposed copper in the box. If that's the result of your work, you're almost definitely doing it wrong -- you should only be stripping enough insulation to make your contacts happy, and it's rare that you'd ever need more than 1/2" stripped (and all of that would be inside a wire nut, or wound around a screw, or otherwise obscured).
posted by range at 6:19 PM on October 4

Moved the ground so we could get the cover on, but it touched (it had a long section of exposed metal) the copper connector part (the part connecting the appliance wires to the appliance) causing the zap

This shouldn't be able to happen. Get a licenced electrician in to make sure it doesn't happen again.
posted by flabdablet at 6:49 PM on October 4

It's always possible to align a bare ground wire in a wonky way so that it makes an inadvertent connection to the hot or neutral contacts. I hate the way you wire up a receptacle in the US and then have to force it back into the box. For this reason experienced electricians use small bits of electrical tape to cover the contacts.

I don't see any reason the appliance isn't safe to use afterwards, although a short could always do something like burn out a digital control board.
posted by dhartung at 9:23 PM on October 4