I am not an especially handy guy but I’m trying to learn. I just bought a house that was built in the 1930s. The previous owner lived in the house since 1952, and it doesn’t appear that many upgrades have been made during that time. (And all the carpeting and wallpaper seems to be from the fifties, too, but that’s another story…)
Yesterday, I replaced one of the old ceiling light fixtures with a new one, which seems simple enough, but I’ve never done this sort of thing in an old house. The light fixture works fine, but now I’m wondering if I did this correctly and/or safely.
So I have two basic questions, and none of the online sources I could find gave me reassuring answers.
The old electrical box had three thick copper wires in it. Two were twisted together and the third was alone. Does it matter which wire I connect to which on the fixture? What’s the purpose of the pair of wires? I guessed that this meant electricity was running from this box to one of the wall outlets in the room, but I don’t know.
The new fixture came with a green ground wire. The old fixture didn’t have one, and there’s no ground wire in the ceiling box. Is it adequate to attach the wire to the box with a grounding clip? And just for my own information (not that I intend to do this) what are the consequences if I just left it ungrounded altogether?
I have replaced fixtures, outlets, and wall switches in newer houses without difficulty. I just want to be sure I understand the older wiring and don’t do something that leads to the house burning down. Any dopers have general advice about doing this sort of basic electrical work in such an old house.
It doesn’t really matter which wire on the fixture goes to which wire in the j-box unless the installation instructions for the fixture say it matters. If there is no marked neutral wire in the fixture you’re fine.
Connecting the ground to the box is fine but pointless. You’re supposed to upgrade the wiring to include a ground when you make changes, but it’s not terribly important for a light fixture.
It’s a fluorescent light (this one, fwiw ), so I don’t think heat will be an issue. But I will keep this in mind as I replace other light fixtures. I assume that the fire risk exists with the old fixtures to, since they are all inefficient incandescents.
Thanks for the info, Gus, and thanks for the links AR Cane.
With an incandescent light fixture, the socket shell, or threaded portion should connect to neutral, and the tip connection at the bottom should connect to hot. Reverse them, and the light will still function, but it’s still not as it should be.
The risk of fire exists with the old fixtures, but the risk increases when you bother the wires. The insulation is probably very brittle by now, so the stress on the wires from being moved while changing the fixture can cause cracks in the insulation which can lead to arcing and fire.
The black wire, if any, on the fixture connects to the black, or colored, wire in the box. The white wire on the fixture goes to the white wire in the box. On things like outlets, the black, or colored, wire goes to the brass screw. The white wire goes to the silver screw. Since your wiring doesn’t have a safety ground, just leave the green wire alone. It doesn’t hurt to connect the green wire from the fixture to the box but all that does is keep it out of the way.
The problem I have here is that the wires in the box are both black. So I guess my query was whether I need to use a meter to determine which is which before connecting the fixture, or whether it doesn’t matter.
It doesn’t matter to the operation of the fixture, but the safest way is to connect it so that the hot line is connected to the black lead and the neutral is connected to the white. Connect your voltmeter between one of the wires in question and the fixture box, which should be grounded. If you get ~110-120 V, that’s your hot.
To make the bulb light up, no it doesn’t matter. If you don’t want a shock when you screw in a new bulb, you should connect white to white and colored to colored.
Most people turn the light off before changing a bulb, so no part of the socket will be electrified. It’s nice to hook up the hot and neutral wires correctly but in practice many fixtures make it difficult by not identifying the neutral. I would wager that as many fixtures are crosswired as are wired correctly.
As you put together a list of things to do in the upgrade process, you really should plan on replacing the wiring. If for example, you plan to insulate the walls, replacing the wiring first is a lot easier.
I’ve lived with post and knob wiring and the early versions of romex and it can get quite interesting when the insulation on the wiring falls off from old age.
Not always, some older homes are wired so that the neutral is switched, not the hot.
I bet not. In order for a fixture to get UL approval it has to have the neutral wire go to the screw shell.
In addition, the old wiring in the home can be sleeved with shrink wrap insulation if the existing wire is brittle. Also, checking with a meter for the hot wire (when all wires are old and appear black) may not get you anywhere if the box is not grounded. I’ve had to run a lead to the nearest neutral at an outlet and then up to the fixture box to determine which wire was the hot. Else, you can get one of the various voltage sensors on the market. It will beep/flash when it comes close to a hot wire.
Likely what you have in your ceiling box is a single hot and two neutrals. The hot wire comes from the switch and the neutral is spliced through. The box itself is unlikely to be grounded.
Could you offer a NEC cite for that being permissible? My understanding has been that disconnection of the line or both line and neutral was acceptable, but not the neutral alone.
As uncommon sense said, I don’t think it’s legal, but it’s done. Just like (I don’t think) wiring a fixture backwards isn’t legal, but it’s done as well.
I think the thing is, someone wanted a light to be on a switch so they grabbed a wire and put a switch on it with out really thinking about which wire it was, as long as the light turned on and off.