Trying to make sense of wiring...

[jsmyle]

I am hanging a ceiling fan and found the following when I dropped the light:

1) There are 3 romex cables coming into the box. I will call them A, B and C.

2) Ground wires (bare): A & B are twisted together and loose in box...each wire is about 3 inches long. C is grounded to box.

3) Black wires: A & B are twisted together and capped off with a wire connector. They are pushed back in box (unconnected). C is twisted together with B's white wire and connected to black wire from ceiling light.

4) White wires: A & C are twisted together and connected to white wire from ceiling light. As mentioned above, B is tied together with C's black wire from C and connected to black wire from ceiling light.

Is this, which appears to me as a mess, correct? Should I: (a) hang my ceiling fan and maintain the current wiring arrangement, (b) use only the wires on C and cap of A & B with wire connectors, or (c) call an electrician?

Thanks.

[Eric in North TX]

One of those is likely a switch wire, you'll need that, the other "extra" wire likely is a daisy chain to another light fixture. This is really pretty minimal, I have no less than 6 sets meeting at my first ceiling box in my living room, something I intend to change one day, as the light and outlets share a circuit. That was common old school practice, but less common and no doubt illegal today.

[Doug Miller]

All three should be connected to each other and to the box. The easiest way to accomplish this probably is to detach C from the box, attach a length of bare wire (6-8") where C was attached, and wire-nut that wire together with A,B,&C.

What do you mean, "unconnected"? They're connected to each other, aren't they?

Looks like A supplies power to the box, and B is a switch leg for the light. Current goes to the switch on cable B's black wire, and returns on B's white wire. C apparently supplies power to a second light (or perhaps an outlet) controlled by the same switch.

Sounds good.

Probably it is.

Yes. Why would you do anything different?

If you do that, it will stop working. So will the other light (or outlet) controlled by that switch.

That might actually be your best bet, since (no offense intended) it appears that you don't really understand the situation.

[Goedjn]

If I understand your description properly, then I expect that (A) is coming from the service panel, and feeding a hot and a ground to (B), which is returning a switched hot on the white wire, {which therefore ought to be marked in some way.}

That switched hot is supplying both the light fixture, and something else off on the other end of cable (C).

The nuetral coming back from whatever's on the other end of (C) combines with the nuetral off the light, and goes back to the service panel on the white wire from (A).

If this is correct, then the ground wires are wrong, since the ground from the mystery device is connected to the box here, but not to the ground that leads to the service panel. All three grounds should be twisted together, along with one from the box itself.

Note that you don't have enough wires from the switch to SWITCH both a light and a fan, but since you've got an always-hot wire from the service panel, you can supply the fan from that, and use the pull-chain to control the fan.

So you'll want [ (A,black) (B,Black), (fan) ] = Supply

[ (B,white) (C,black), (light) ] = Switched [ (A,white) (C,White), (fan/light, white) ]

and [ (A, ground) (B, ground) (C, Ground) (Box-Ground) ]

....

--Goedjn.

ps. Always assuming I've guessed right about what the current wires are doing.

[Joseph Meehan]

OK I have not really thought this out, so this is just a quick non-certified reply.

It appears to be a light with pass through power and a switch line.

There appears to be an error in that all three grounds should have been connected (and attached to the box). A second possible error may be the lack of remarking the color of the wire to the switch. I seem to recall that current code requires marking the ends of the wire in this case.

[N8N]

It does, but I believe that that is a recent addition to the code so it may not have been a violation when the work was done.

nate

[John Grabowski]

In addition to being grounded to the box the "C" grounding conductor should also be connected to "A" and "B" as well as the grounding conductors from the ceiling fan.

Yes if you want the fan to work just like the currently installed light fixture, wire it the same way. Is the electrical box that currently supports the existing light fixture rated for ceiling fans? If not then you will need to remove it and install a fan brace and box. Make sure to identify each conductor before taking them apart.

(b) use only

[mgkelson]

My suggestion would be to simply maintain the current wiring arrangement. It's not really a mess unless the box is to small. You should probably connect ground wires A&B to the box if there's room in the box to do so. If there isn't room, I think I would leave it alone or swap out the box.

Your biggest problem is in bracing the box so that it can carry the weight of the ceiling fan. I did that once and as I recall, I precut a piece of 2 x 4 lumber and screwed it on to the ceiling trusses and then screwed the electrical box on to the 2 x 4. I think I actually replaced the box while I was at it, but I wouldn't do that unless you have to.

[Nate Nagel]

I *would* replace the box if there is access from above. I believe most ceiling fans want 10-32 screws not whatever the standard ceiling box is (6-32?) also a proper fan box will have more secure holes for the screws to thread into than the bent tabs on a regular ceiling box.

nate

[Nate Nagel]

Just put a strip of tape (red or black) around the end of any white wires used for switch legs whenever you find them so future generations aren't confused. no problem.

nate

[Mark Lloyd]

This house (built around 1969) has several switch loops, none of which are marked. also the 240V circuits use ordinary 10/2 Romex (black/white/bare), and aren't marked either.

[Mark Lloyd]

That would mean removing ceiling light fixtures (since that's the way this place is wired), but I should be able to do that.

[Nate Nagel]

I didn't mean that you should mark everything in the house now; just if you are working on something and determine that there's an unmarked switch leg, it only takes a few minutes to mark it. Obviously you are now aware that there *are* switch legs, so you'll be looking for them in the future and will be aware that some white colored wires may be "hot."

nate

[Goedjn]

It's not worth opening the boxes just to do that. You should just remember to mark them if you're ever in there for some other reason. The less you mess with the wires, the happier they'll be.

[mgkelson]

I didn't know there were special electrical boxes available for ceiling fans. The only installation I ever did was back in about 1985 and I just sort of jury-rigged everything with 2x4s, etc. The fan is still hanging there so I must have done OK :>

It could be, though, that the special boxes were available even back then and I just didn't know it.