9

USA - I’m installing a new ceiling light fixture in a bathroom. The instructions (and every how-to video I watched) said to connect white to white (neutral) and black to black (hot). However, when I detached the old fixture, I found the opposite: the white wire was connected to black and vice versa. It’s been like that for years. Should I connect the new fixture the way it was previously, or follow the instructions? And what could potentially happen if I do it the wrong way? In case it matters: there is also another light fixture in the same room that is controlled by the same switch. First picture provided is the existing configuration. I stopped and left it the way it was because I wasn’t sure how to proceed.

EDIT: I have now added a second picture of the existing wiring at the switch. There are two switches at this box. The switch on the left controls a fan in the ceiling. The switch on the right controls the light fixture in question along with another light fixture. There are 4 sheaths coming into/out of the switch box, each of which has one black wire, one white, and one ground. I’m not sure which of these delivers power from the house, and which go out to the lights and fan.enter image description hereenter image description here

17
  • 6
    Traditional incandescent fixtures with sockets for bulbs are wired so that the shell of the socket is neutral and the base contact is hot. That reduces the likelihood of getting an unpleasant surprise while changing bulbs when the circuit is energized, You may be able to visually confirm the connections and can certainly do so with a multimeter. – HABO May 3 at 3:27
  • 1
    This may be a hack job by somebody used to work on automotive or boat wiring. Black was often used for the negative on a DC 12v circuit (often referred to as the ground when the chassis wasn't used for the negative. The only way to be sure is to test with a multimeter or open up the switch controlling the light and examine the wiring. – George Anderson May 3 at 5:09
  • 16
    This was clearly installed improperly. In this situation, don't even trust the wiring coming in. Test - and make sure the white wire is actually neutral. Maybe Joe DIY installed this device box too and got the wires wrong at the other end - then flipped the lamp connections to make it "good" again. Don't trust anything. Get a tester and test. This is a red flag. Ignore it at your peril. – J... May 3 at 11:29
  • 8
    When doing electrical work not having a voltage tester is not an acceptable option. At the big box store with orange buckets a non-contact tester is $6, and a led voltage tester is $13. – NoSparksPlease May 3 at 16:23
  • 2
    I have now updated the original question to add a picture and description of the existing wiring at the switch that controls the light fixture in question. I can’t really make sense of it though to be honest. – Matt Leonard May 4 at 3:14
11

OK, I'm sure it's clear to you that the white should be connected to the white, and it should be the neutral.

But just switching the wires really is an incomplete solution, you know they did something wrong, but how wrong? At very least you need a tester to verify that the black is the hot and it is the switched wire. This can simply be done with a no-contact tester or with a volt meter with one lead connected to the bare ground and the other lead testing the black and white for voltage. The black should be the switched hot. If not then you need to at least trace the cable back to it's source, probably the other light, but possibly the switch. It is unlikely but possible that they could have run two switched cables from the switch, rather than one cable from the switch then one cable between lights.

If you find that the wires feeding the junction box are correctly polarized but the fixture is just connected wrong that really wouldn't give me peace, I wouldn't know if it was a single moment of inattentiveness or a pattern inability to follow safety codes. I would want to open the other fixture and probably the switch to verify correct connections. You could then post follow up questions if anything else looks awry.

T̶h̶e̶ ̶o̶n̶l̶y̶ ̶p̶l̶a̶c̶e̶ ̶y̶o̶u̶ ̶s̶h̶o̶u̶l̶d̶ ̶s̶e̶e̶ ̶a̶ ̶w̶h̶i̶t̶e̶ ̶c̶o̶n̶n̶e̶c̶t̶e̶d̶ ̶t̶o̶ ̶a̶n̶y̶t̶h̶i̶n̶g̶ ̶b̶u̶t̶ ̶o̶t̶h̶e̶r̶ ̶w̶h̶i̶t̶e̶s̶ ̶i̶s̶ ̶i̶n̶ ̶a̶ ̶g̶r̶a̶n̶d̶f̶a̶t̶h̶e̶r̶e̶d̶ ̶t̶w̶o̶-̶c̶o̶n̶d̶u̶c̶t̶o̶r̶ ̶s̶w̶i̶t̶c̶h̶ ̶l̶o̶o̶p̶.̶ ̶I̶n̶ ̶m̶o̶s̶t̶ ̶n̶e̶w̶ ̶i̶n̶s̶t̶a̶l̶l̶a̶t̶i̶o̶n̶s̶ ̶a̶ ̶n̶e̶u̶t̶r̶a̶l̶ ̶i̶s̶ ̶n̶o̶w̶ ̶r̶e̶q̶u̶i̶r̶e̶d̶ ̶a̶t̶ ̶t̶h̶e̶ ̶s̶w̶i̶t̶c̶h̶ ̶t̶o̶ ̶a̶l̶l̶o̶w̶ ̶t̶h̶e̶ ̶o̶p̶e̶r̶a̶t̶i̶o̶n̶ ̶o̶f̶ ̶o̶c̶c̶u̶p̶a̶n̶c̶y̶ ̶s̶e̶n̶s̶o̶r̶s̶,̶ ̶s̶o̶ ̶a̶ ̶s̶w̶i̶t̶c̶h̶ ̶l̶o̶o̶p̶ ̶w̶o̶u̶l̶d̶ ̶r̶e̶q̶u̶i̶r̶e̶ ̶a̶ ̶b̶l̶a̶c̶k̶/̶r̶e̶d̶/̶w̶h̶i̶t̶e̶ ̶c̶a̶b̶l̶e̶ ̶w̶i̶t̶h̶ ̶b̶l̶a̶c̶k̶ ̶a̶n̶d̶ ̶r̶e̶d̶ ̶u̶s̶e̶d̶ ̶a̶s̶ ̶h̶o̶t̶ ̶a̶n̶d̶ ̶s̶w̶i̶t̶c̶h̶l̶e̶g̶s̶.̶ ̶I̶n̶ ̶a̶ ̶g̶r̶a̶n̶d̶f̶a̶t̶h̶e̶r̶e̶d̶ ̶i̶n̶s̶t̶a̶l̶l̶a̶t̶i̶o̶n̶ ̶a̶ ̶f̶i̶x̶t̶u̶r̶e̶ ̶i̶s̶ ̶f̶e̶d̶ ̶w̶i̶t̶h̶ ̶a̶ ̶h̶o̶t̶ ̶a̶n̶d̶ ̶n̶e̶u̶t̶r̶a̶l̶,̶ ̶t̶h̶e̶ ̶w̶h̶i̶t̶e̶ ̶n̶e̶u̶t̶r̶a̶l̶ ̶i̶s̶ ̶c̶o̶n̶n̶e̶c̶t̶e̶d̶ ̶t̶o̶ ̶t̶h̶e̶ ̶l̶i̶g̶h̶t̶,̶ ̶t̶h̶e̶n̶ ̶t̶h̶e̶ ̶h̶o̶t̶ ̶(̶b̶l̶a̶c̶k̶)̶ ̶i̶s̶ ̶c̶o̶n̶n̶e̶c̶t̶e̶d̶ ̶t̶o̶ ̶s̶e̶p̶a̶r̶a̶t̶e̶ ̶b̶l̶a̶c̶k̶/̶w̶h̶i̶t̶e̶ ̶c̶a̶b̶l̶e̶ ̶t̶h̶a̶t̶ ̶l̶e̶a̶d̶s̶ ̶t̶o̶ ̶t̶h̶e̶ ̶s̶w̶i̶t̶c̶h̶.̶ ̶I̶n̶ ̶t̶h̶e̶ ̶s̶w̶i̶t̶c̶h̶ ̶c̶a̶b̶l̶e̶ ̶t̶h̶e̶ ̶w̶h̶i̶t̶e̶ ̶i̶s̶ ̶(̶s̶u̶p̶p̶o̶s̶e̶ ̶t̶o̶ ̶b̶e̶)̶ ̶m̶a̶r̶k̶e̶d̶ ̶w̶i̶t̶h̶ ̶t̶a̶p̶e̶,̶ ̶i̶n̶k̶,̶ ̶o̶r̶ ̶p̶a̶i̶n̶t̶ ̶a̶n̶d̶ ̶t̶h̶e̶n̶ ̶i̶s̶ ̶u̶s̶e̶d̶ ̶a̶s̶ ̶a̶ ̶h̶o̶t̶ ̶b̶e̶t̶w̶e̶e̶n̶ ̶t̶h̶e̶ ̶l̶i̶g̶h̶t̶ ̶a̶n̶d̶ ̶t̶h̶e̶ ̶s̶w̶i̶t̶c̶h̶.̶ ̶T̶h̶e̶ ̶b̶l̶a̶c̶k̶ ̶t̶h̶e̶n̶ ̶r̶e̶t̶u̶r̶n̶s̶ ̶t̶o̶ ̶t̶h̶e̶ ̶l̶i̶g̶h̶t̶ ̶a̶s̶ ̶t̶h̶e̶ ̶s̶w̶i̶t̶c̶h̶l̶e̶g̶ ̶t̶h̶a̶t̶ ̶i̶s̶ ̶c̶o̶n̶n̶e̶c̶t̶e̶d̶ ̶t̶o̶ ̶t̶h̶e̶ ̶b̶l̶a̶c̶k̶ ̶f̶i̶x̶t̶u̶r̶e̶ ̶l̶e̶a̶d̶.̶ ̶(̶I̶f̶ ̶t̶h̶e̶ ̶b̶l̶a̶c̶k̶ ̶w̶a̶s̶ ̶u̶s̶e̶d̶ ̶a̶s̶ ̶a̶ ̶h̶o̶t̶ ̶d̶o̶w̶n̶ ̶t̶o̶ ̶t̶h̶e̶ ̶s̶w̶i̶t̶c̶h̶ ̶t̶h̶e̶n̶ ̶t̶h̶e̶ ̶w̶h̶i̶t̶e̶ ̶w̶o̶u̶l̶d̶ ̶h̶a̶v̶e̶ ̶t̶o̶ ̶b̶e̶ ̶u̶s̶e̶d̶ ̶t̶o̶ ̶t̶h̶e̶ ̶l̶i̶g̶h̶t̶,̶ ̶w̶h̶i̶c̶h̶ ̶w̶o̶u̶l̶d̶ ̶r̶e̶s̶u̶l̶t̶ ̶i̶n̶ ̶t̶w̶o̶ ̶w̶h̶i̶t̶e̶s̶ ̶t̶o̶ ̶t̶h̶e̶ ̶l̶i̶g̶h̶t̶ ̶f̶i̶x̶t̶u̶r̶e̶.̶ ̶T̶h̶e̶ ̶w̶r̶i̶t̶e̶r̶s̶ ̶o̶f̶ ̶t̶h̶e̶ ̶c̶o̶d̶e̶ ̶t̶h̶o̶u̶g̶h̶t̶ ̶t̶h̶a̶t̶ ̶w̶o̶u̶l̶d̶ ̶c̶r̶e̶a̶t̶e̶ ̶m̶o̶r̶e̶ ̶c̶o̶n̶f̶u̶s̶i̶o̶n̶.̶)̶ ̶

Edit: After seeing your updated picture any talk about switch loops and white being marked and used for anything but neutral doesn't apply, which is good. But since you indicated there is another light on the switch that controls this light, and since the light shown is an end-of-line you still need to verify proper polarity of the wires feeding the light isn't reversed in the intermediate fixture. If you refuse to get a voltage tester a redneck method to verify the polarity at the end light would be to disconnect the white fixture wire from the black building wire, then connect the white fixture wire to the bare building wire. If the switch turns the light on then you need to take apart the other fixture and connect all wires color for color. If nothing happens when you turn the switch on then just connect color for color in that end-of-line j-box and you will be good to go.

7
  • 2
    This answer is a little bit "wall of text" but I'm upvoting it because it is the only one that recommends you try to UNDERSTAND the problem better before fixing it. I'd use a volt meter myself. take off the fixture and turn on the switch. make sure black has voltage to ground and white does not. you identified one backwards connection. who's to say it's not backwards on the other side too? – Billy C. May 3 at 18:00
  • I could get a voltage tester - sounds like that is probably a good idea. I’m just not sure I would know how to use it correctly. But I could give that a try. I appreciate all the info! – Matt Leonard May 4 at 13:04
  • @MattLeonard If you do not have confidence in your ability to learn a new skill correctly, or in your ability to assess your own learning, hire an electrician. It's as simple as that. – J... May 5 at 11:28
  • 1
    To follow up: My landlord stopped by with a voltage tester and we determined that the black wire coming out of the ceiling was in fact hot. So we installed the new fixture connecting black to black per the instructions and everything seems good to go! – Matt Leonard May 6 at 1:46
  • @MattLeonard Wait... your landlord?? If you're a tenant you should not be doing electrical work on your landlord's property - for a myriad of reasons, not the least of which is that you're not qualified and it's not your house. You're lucky your landlord is crazy and didn't evict you or sue you. – J... May 6 at 9:40
15

An Edison bulb has a metal "tip" that is totally inaccessible once you start screwing it in. It does not make contact with the socket until it's screwed all the way in.

It also has an outer metal threaded screw base, which is easily touched while screwing it in. It makes contact with the sockets "shell" immediately and continuously while screwing it in.

The socket's shell is attached to the white wire. If you connect that to neutral, then touching a bulb's socket while screwing it in will be harmless unless there's a wiring fault.

Of course if you connect the socket shell to hot, then if you forgot to turn the switch off, you can get nailed by your finger touching the shell as you screw it in.

0
3

This points out the need for understanding the basics of wiring. The light fixture must have a neutral from the house connected to the neutral on the fixture, and will have a switched hot from the switch box connected to the hot connection of the fixture.

The neutral from the house wiring will always be white. If the fixture has wire leads, the fixture neutral will always be white so the neutral connection to the fixture will always be white to white.

The switched hot from the switch however can be either black or white. Therefore, the connection to the hot lead on the fixture can be either black to black or white to black. When a white wire is used as a hot or a switched hot it is supposed to be marked with black tape or a black marker around each end.

EDIT

There are two ways the house wiring can power a ceiling fixture controlled by a wall switch:

(1) The cable from the house (black always hot, white neutral) goes into the switch box. The black line hot connects to one side of the switch. The white neutral connects to the white of a cable going to the ceiling box.

In the ceiling box the black wire is switched hot and connects to the black lead, and the white is neutral and connects to the white neutral lead of the fixture.

(2) The cable from the house enters in the ceiling fixture box. In the old wiring method the white neutral connected directly to the white neutral of the fixture and stopped there. The black line hot was connected to either the black or the white of a cable with only black and white going to the switch box. The other wire of the cable was connected to the black lead ofvthe fixture.

In the switch box the two wires (one black and one white were connected respectively to the two contacts on the switch so the white wire either carried the line hot to the switch or the switched hot to the fixture. In this arrangement there was no neutral in the switch box which was OK because the simple mechanical switch did not need one.

Nowadays it is required to have a neutral in the switch box (new construction only) so if the line hot enters in the ceiling, then a three conductor cable (black, red, white) would be required between the ceiling fixture box and the wall switch. The white would be neutral, and the red and black would carry the hot and the switched hot and be connected to the two connections on the switch.

The white neutral would only be connected to the switch if the switch was one which consumed power, e.g., an electronic timer or a smart switch.

3
  • 1
    the fixture neutral will always be white ...if it was installed by a competent person. I have certainly seen boxes where the fixture neutral was not white - the more red flags a box has, the less you can assume is done correctly. – J... May 3 at 14:31
  • I was thinking of factory installed fixture wiring. – Jim Stewart May 3 at 16:40
  • Fair, I meant to quote The neutral from the house wiring will always be white - sorry, grabbed the wrong text. – J... May 3 at 17:01

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.