The ceiling electrical box in my kids bedroom only has a single red and single black wire, but nothing else (no white wire, no bare copper ground wire, not even a grounding nut). I bought a ceiling light fixture which has the standard black, white and copper wires (hot, neutral, ground), but I've no idea how to connect these to the ceiling box and would prefer not to guess. Any help would be appreciated.

Do you have a tester? Is the box metal and grounded to conduit or armored cable? Chances are good you actually have a hot and a neutral just not the right colors. I run into all sorts of things like this when remodeling, just never know what the guy before you was doing.

Thanks for your reply. I did check the potential across the 2 wires, with the light switch OFF it's 0V, with switch ON it's 120V. The ceiling box is plastic and held in with 2 screws, neither of which is grounded. Nothing else in the plastic box is ground and no other wires. I haven't pulled the box to see what's behind it, so not sure how the red/black wires were routed to it. What I did was connect the light fixture black to ceiling box black, and light fixture white to ceiling box red, and the light seems to work fine (turn on and off with room switch). I don't like leaving the light fixture safety ground floating but without a ceiling box ground I don't have much choice. I suspect since it's a ceiling light that there's not much chance of anyone getting shocked by it if a fault occurred, but it is something I'll have to remember if the light ever starts acting funny... don't touch it... or check to see if it's hot with a meter.

Pilm,

With the switch in the "Off" or "Open" position there should be 120 VAC (+/- 10%) across the terminals of the switch.

With the switch in the "On" or "Closed" position there will be zero (0) volts.

Does the handle of the switch have "On/Off" indicators? If your switch does not have ON and Off embossed onto the handle, then stop there and take pictures of the wiring at the switch and at the overhead outlet box.

Make sure you open the breaker the feeds this circuit before doing any additional work, please.

After the breaker has been opened, I would like you to remove the faceplate on the switch and then remove the yoke. This is the vertical metal plate that contains the switch.

Slide the switch assembly away from the outlet box, do not disconnect it.

I suspect that you are feeding the power to switch in the Off/Open position. Close the switch On/Closed and the power is fed through the switch to the light fixture.

I would expect to find a black wire connected to the bottom and top terminals of the switch and the red wire bypassing the switch and continuing on to the light.

If that is true, then the power feed to the light is via the black conductor. The red conductor would be a re-tasked conductor from a hot conductor to a neutral conductor. Not exactly to code and dangerous.

If this is what you see, then take a White Sharpie or White electrical tape and color the Red Conductor with the white marker at both ends.

If you see anything else, please take pictures of both ends of the cable and post them to this item using the "Advanced" tab below.

What Plim measured makes sense to me - measuring across the wires in the ceiling would be 0 V with the switch off, and 120 with it in the on position. As far as how you connected the wires Plim, it really does not matter with AC. Both would have worked the same. Ideally you would do white to white and black to black, but you did not have that option. I am guessing your house was built some time ago, or the previous owner wired the box up there without regard to electrical codes. If you are worried about not having a ground, if the area above this room is unfinished space (e.g. and attic) you could climb up there and run a single ground wire from some other circuit to that box and connect the bare metal wire to that. Or even better, if you are a go-getter, you could just snake a 14/2 cable from the switch to the box in the ceiling using electrical fish tape. Would not be too hard if you have attic access.

Dm,

I agree with the measurements also, however it doesn't get you any closer to solving the wiring riddle.

The switch needs to be inspected for correct operation because reversed wiring does make a difference with respect to knowing which wire should be connected to the neutral conductor in the ceiling.

To know that, you need to know how the switch is configured and then you need to properly identify the correct neutral conductor.

Hey Don - I was not aware that it really mattered with a simple AC light which was hot or cold, and that it would work fine both ways since the light is effectively a resistor in series with the light switch. Is this not the case?

Thanks!

What happens when you connect a hot line to Neutral with no load in the middle?

A short, and hopefully a tripped breaker :-) Agreed. And with a load, all works as expected with no issues.

Correct, now, which is Neutral and which is Hot?

You need to see the switch to know whether the feed to the light is either the Black conductor or the right conductor so you will know which is which at the ceiling jbox.

Hi Don,

Yes, the switch handle shows OFF when down, ON when up, and the voltages read just as you indicate for each position.

I took some pictures of the light switch box wiring. It was a mess of wires inside there, not quite what I expected! Picture 1 is an overall shot with the cover plate off and toggle switch partially pulled out, picture 2 is close up showing how the toggle switch is wired, and picture 3 (which is rotated so the top is on the left) shows white/black wires tied together, as well as a wire bundle in lower left consisting of red, black, white and ground wires (not 14/2). I checked voltage on the toggle switch screws with the switch OFF, the upper red wire was 120V and the lower was 0V relative to ground. With the switch ON both upper and lower red wires were 120V to ground. I assume this means the supply is coming to the top screw red wire and the bottom red wire goes to the ceiling box (this is mostly confirmed because the bottom red wire is stranded wire while the top is solid wire, and the red wire at the ceiling box is stranded wire). So I think this means the red wire in the ceiling box is toggled hot while the black wire is return (picture 1 shows this black wire in the upper right, where you can see it is tied to a white wire with the wire nut - note in the pictures that the white wire appears somewhat yellow, due to my camera and lighting). So if I read your post correctly, this means I should change the light fixture I connected to the ceiling box from black-black and red-white to red-black and black-white.

One thing I'm unclear on is on the toggle switch, I was surprised to see a black wire going into the back of the toggle switch (not to a screw but inserted into the back of the toggle switch, see picture 2). Any idea why that was done? It doesn't appear that this black wire is tied into the wire nut that tied the black wire from the ceiling box to the white neutral/return wire, so I'm not sure what this is about. Also, the yellow conduit bundle (picture 3) has four wires, red, white, black and ground, which doesn't seem to be normal household wiring, so I'm wondering why someone would do it? Note the house was built 2003 and probably to code but I suspect the prior owner had his hands in the box and may not have known exactly how to do code wiring, but why introduce a 3 wire colored cable?

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Who ever did this wiring should be dragged in front of some seriously incensed, mad, wives with stones and sharp instruments in their hands.

I did some PhotoShop magic on the pictures for you.
Please turn the BREAKER "OFF"

#1 - Using white tape or a white sharpie, color the black wire that is inside the wire nut with two other white wires. This conductor needs to be marked as a re-tasked conductor. This black wire is being used as a Neutral. It will connect to the White wire coming from the light fixture.

#2 - The Red conductor is going to be your hot conductor. It will connect to the "Black" wire coming from the light fixture.

#3 - With the breaker in the "OFF" position, I would remove and cap off the black wire that is back stabbed into the switch. If it is needed for something else it needs to be on a separate switch or replace the switch with a three way switch.

#4 - If there are any bare uncapped conductor ends, they must be capped off.

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Don,
Thanks for the comments and updating the pictures, I know exactly what to do now. I'm still a bit perplexed why someone stuck a black wire in the back of the toggle switch but I'll get over it. Thanks again!