I am replacing a bathroom light fixture. The light fixture I am installing has one set of wires (1 black, 1 white, 1 ground). The ceiling box has 3 sets of wires (3 black, 3 white, 3 ground). How do I wire the new fixture?

How was the old fixture wired?
Are any of them spliced together?

Stan, I don't exactly remember, because I removed the old one prior to purchasing the new one. But I believe that one set of wires was spliced to another set (White to white, black to black, ground to ground).

You might take the cover off the light switch controlling the fixture and look inside; if a white wire and a black wire are attached to the switch, you are dealing with an end of the run switch, and one set of cable in your ceiling box would be going on to another fixture. If two blacks are attached, then it is something else, and it would make sense that you said one set was spliced to another. Hope this helps.

What wires were connected to the old fixture? Did you remove the wire nuts?

I don't remember exactly, but I believe the old fixture had 2 sets(1 black, 1 white, 1 ground) of wires. And then two sets coming out of the ceiling box were spliced together, making a matching 2 sets to 2 sets. The problem is my new fixture only has one set of wires.

In the bathroom where you are working, is there a wall switch?

Normally, each cable will contain the B/W-g wires.

Since you have three cables in the ceiling, it suggests to me that you have one switch loop in the mix.

Step one would be to find out which cable is the supply cable. If you have a volt meter, test for voltage at each B/W pairing.

Once you have isolate that cable, then switch the meter to Ohms and test the other pairs by connecting to the b/w pair. With the switch in the "Off" position, there will be infinite continuity between the two wires. With the switch in the "On" position there will zero (0) resistance. If you are using an analog meter (one with a needle) you will see the needle deflect all the way to the right.

If you have a digital meter, the indicator will go to zero and the meter may "Beep".

Once you have the supply cable and the switch loop identified you are ready to make connections.

Take the white wire from the switch loop the black wire from the supply and the third black wire and connect all three with a wire nut. At this time, also, either place a piece of black tape or use a magic marker and color the white from the switch loop. This is called re-tasking the conductor.

With that completed, take the white from the supply cable, the white from the new fixture and the white from the third cable and connect them together with a wire nut.

Lastly, take the black from the switch and connect it to the black from the new fixture.

FYI - The NEC allows the use of the white conductor as a hot conductor when used in a switch loop. However, the NEC limits its use to carrying the power from the supply to the switch. It cannot be used to return the power from the switch to the device.

It is common for a fixture-luminair- to have a single black and white for each light. You may find these have been bundled in the new light. I would connect all the blacks, all the whites and the ground wires. Hang the fixture temporarily with a coathanger hook and turn it on. If it works, turn it off and go ahead with the install. If it doesn't work, follow Donf's testing process. Good Luck, Brian

I would go ahead and connect all the blacks, all the whites and the ground wires. Hang the fixture temporarily with a coathanger hook and turn it on. I personally would NOT do this. I agree with Don that a switch loop is probably in the mix. Connecting all the blacks and all the whites will more than likely create a direct short.

Unfortunately this is pretty typical scenario where someone removes a fixture and feels the need to unsplice EVERY wire in the box. To anyone reading this, for future reference, DO NOT do this. Only remove the fixture wires and leave all other splices intact. That, or label every wire and keep track of what was what.