bonding electrical box to siding? safe?
This weekend, I was inspecting my entrance overhead light fixture to install a new light fixture.
My home electrical is primarily non-grounded 2-wire ROMEX with old cloth braided sheath (1951 construction).
It appears that the current light fixture is fastened to a metal pancake ceiling box, installed rather sloppily, and that box and fixture are bonded to the aluminum siding. The electrical cable does not have a ground wire. Some previous owner or electrician had a green insulated ground wire bond the fixture, box, to someplace behind the siding. I can only guess that it is grouding to the siding, that is grouded with its own ground rod (I think, but have not definitively located that ground).
My question is, “Is this dangerous in the current configuration?”
I am thinking that I should put a better electrical box in, like a ceiling fan box and brace, making sure of a good seal between the box and the outdoor light fixture, and getting rid of the green wire ground. Would this help or create a more hazardous situation. The fixture is an outdoor entrance light fixture, that was installed to fit against the metal soffit, which covers the original wooden soffit of the home. The NM cable simply enters the pancake ceiling box through a hole drilled in the soffit, and the box hangs from the cable, not really fastened to anything firmly above it. The light fixture is suspended from the metal soffit by sheet metal screws, which appear OK but the whole thing looks rickety.
I will ask an electrician to look at it when I have him install an outdoor post lamp, but wanted some opinions from here to consider when he comes over.
Replies
I've never heard of a separate ground rod for aluminum siding. Having one would be pointless.
Grounding is really two different things:
1. Having a solid all-metal connection between any metal components of the electrical system, like boxes, conduit, the screws that hold the plates over switches, etc. to the neutral at the service entrance. This is done to make sure that these items can't accidentally go hot, a breaker or fuse will cut the power instead.
2. Having a connection between the electrical system's ground and true earth ground. This will never carry enough current to trip a breaker, but it will make sure that there's never enough voltage difference between the metal parts of the electrical system and true earth to give you a shock. This helps with lightning protection, too.
Bonding aluminum siding to the electrical system is a good idea. Suppose you're putting up Christmas lights, and you nick a hot wire on the aluminum. If it's grounded, it'll blow a fuse or trip a breaker. If not, the siding will become hot.
-- J.S.
But in this case the siding is (apparently) serving to ground the electrical system, not the other way around.The wire from the box to the siding (if indeed it is attached only to the siding) should be removed and a new ground wire run to somewhere in the "grounding electrode system". A separate wire from the siding should also be run to the "grounding electrode system".Before doing anything, though, be sure the existing wire isn't simply running behind the siding to a more proper ground somewhere.
Edited 7/18/2005 1:54 pm ET by DanH
Thank you for you responses.
You are probably closest to the mark in suggesting that maybe the grounding wire is running behind the siding to a proper ground somewhere.
I will search for the green grounding wire termination point throughout the house, in case it is tied into some newer grounded NM cable somewhere in the basement or attic. Otherwise, I guess I will need to have the electrician check it out when I have my lamp post installed.