I recently had to install a ceiling light fixture. The wiring I saw in the junction box seemed odd, and I just wanted to clarify things.

There were 5 black, and 5 white wires in the junction box. 4 of the black wires were connected together, and 4 of the white wires were also connected together. Using a multi-meter, I tested the remaining black and white wires for voltage. The white was 120 V, and the black wire was 0 volts.

- Shouldn't the white have been 0 V, and the black wire 120 V? What
happened here? is this common?
- As the white wire is hot, I'm assuming this has to go to the black wire of
the light fixture, correct?
- I didn't test the voltage of the black, and white wires that had been
connected together. However, would the black wires have been 120 V, and
the white wires 0 V in this case, or is this something that is indeterminate at
the moment?

 

Was that testing to ground? Is this a switch box, or lighting box, or a receptacle box?

 

It's the light box. It's the box in which the wires from the ceiling fixture are connected to other wires. To be sure, here's a picture of what it looks like:

I tested the voltage by touching one of the multi-meter probes to one of the colored wires, white or black, and the other probe to the inside of the light box.

 

What did the fifth white and the fifth black used to be connected to?

Was there an older light fixture there before?

I would connect the fifth black wire to the gold screw or small black wire of the light fixture and the fifth white wire to the silver screw or small white wire of the light fixture. There is a wiring error someplace else (probably at a switch) which I would then try to find and fix although not yesterday.

The bundle of 4 white wires should be zero volts to ground.

THe bundle of 4 black wires could be 120 volts to ground but is really indeterminate because they could be controlled by a switch.

 

Yes, the 5th black and white wires were connected to a previous light fixture. I'm just not sure how.

Since the 5th white wire is hot, shouldn't that go to the black wire of the fixture. Then, then 5th black, neutral, to the white of the fixture?

 

Propagating an error is not the way to go. If you can find the other end of the 5th wires, usually in a switch or junction box, you will see the 5th white wire connected to a black wire and the 5th black wire connected to a white wire. After shorting the the 5th black and white wires going to the lamp (removes the power to this circuit), switch the 5th black and white wires at the switch or junction box and wire the 5th black wire to black and 5th white wire to white at the lamp. Hopefully the junction box for the light has an earth ground connection. Reset circuit breaker or replace fuse to repower the circuit. If you can't find the other end of the fifth wires, call an electrician.

 

It is quite possible that you are dealing with a switch loop that was not re identified. The white is the constant hot.

 

Is there a way to tell if it is a switch loop or not?

I do know the white is hot.

I just don't know how to tell if it is a "constant hot" that is being referred to.

 

Look at the switch. Are there only a black and white on the switch terminals?

 

Yes, look at the switch. If it has only one 2-conductor cable and the black and white wires are connected to the switch then it is a switch loop. However something is still not right. If the two wires of the cable were not connected neither should be hot.

 

With both the hot white and the dead black coming out of the same cable and loose at the light fixture box these two wires are not a switch loop.

Even in a switch loop, the wire bringing switched power (non-constant hot) to the light fixture (fixture gold screw or small black lead) must not be white even if marked (re-identified) with black.

 

Yes, the switch does have only one 2-conductor cable, and both wires are connected to the switch.
Here's a picture of the switch, link

When I took the voltage reading, the two wires of the cable were not connected, but the fuse was on, and I had turned on the switch in order to get a voltage reading.

Is this a switch loop ?

 

If it is you shouldn't get a reading. With the two wires disconnected measure between the black and white. If you still get a reading something isn't connected right. Double check they are really from the same cable.

Here is a basic switch loop just to give you a better idea.



As you can see if the two wires of the switch loop were disconnected at the light there is no source of power.

 

The cable entering the switch box with both white and black attached to the switch is a switch loop.

The two loose wires, white one hot, entering the light fixture box are not the same two wires and at least the white one is incorrectly connected at its other end..

 

I did some further investigation. There is another ceiling fixture that is connected to the same switch. I took out that fixture as well, and prepared the below wiring diagram of my observations.



I did find a black wire connected to a white wire, 3B-L1 to 1W. The reading across the two wires was always 0V with the switch both ON/OFF. The other 2 white wires in Light 1 were connected together. They were hot when the switch was on, and neutral when the switch was off. Light 2 is the original fixture I was trying to replace.

Does the wiring look ok? I'm not quite sure how the electricity flows in this situation. Any explanation would be appreciated.

 

Your wire colors are swapped. They need to be changed. See changes in diagram below.



DIAGRAM WITH CORRECTED WIRE COLORS

 

I rearranged the wires as indicated. Everything worked out well.

I was curious about another set of ceiling fixtures in the vicinity. They turned out to have the same issue. I fixed those as well using the same principles.

Picture of one of the fixtures with wires corrected, Link

Thank you.

 

How old is this wiring? It seems that making the black wire the switched one and the recoded white wire the hot one was added to the code at some point. In several switch loops I found wired in the 1970s in different houses, the white wire is the switched one. There was also no recoding.

 

The house was built in 1974.