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I have a breaker with at least two light switches on it upstairs. There has been random flickering with LED bulbs, so today I decided to change out the fixtures to see if that was part of the problem. The breaker was on, but the light switch was off while I worked on one set of fixtures. At one point, the white wire (is it called neutral in this case? return?) touched the can/housing (which is grounded) and the other light switch's light got brighter. What would cause this? Is this normal? Or could this be a clue as to what is causing the random flickering?

(I'm aware that I probably shouldn't work on these things while the breaker is on, and that it's not guaranteed to be safe just because the light switch is off.)

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  • Neutral must be white(or grey), but white is not always neutral. Since it did not blow up in your face, it is probably neutral. You know what you did wrong which is good, it is your life. LEDs are weird and will flicker for almost anything, but it might be a clue.
    – crip659
    Mar 11 at 23:16
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    Suspect a broken or loose neutral somewhere. Mar 12 at 0:18
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    @manassehkatz-Moving2Codidact how would I test for this to verify?
    – Reese
    Mar 12 at 6:10
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    @Reese Based on testing you did in response to the answer, that pretty much eliminates a utility-side (i.e., entire house) Lost Neutral. Still could have a lost neutral somewhere in that circuit. Need to check each junction (junction box, pass-through receptacle, light switch box, etc.) between the panel and the light. Mar 12 at 13:56

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The white (neutral) and green or bare (ground) wires should be very close to the same voltage, so if they touch for a second, with good wiring, it should not make any change in brightness.

That change might indicate one of two defects:

A floating neutral

In many locales in North America, the street transformer drops power-line voltage (perhaps 13,000 volts) to 240 VAC, split in the middle (split phase). There are three wires coming from the transformer: 120 VAC-0-120 VAC; since the two 120 VAC outputs are 180° out of phase, three is 240 VAC across them. The 0 (neutral) is grounded at the transformer and at the house.

Household appliances using 120 VAC take power between either hot line and the neutral. 240 VAC appliances, such as stoves and clothes dryers, get power between the two hot lines.

If the neutral line from the transformer to the house is broken, 120 V appliances are connected in series with each other across 240 V. This is not good! For example, a 600 W refrigerator might be on one side of the line, in series with a 100 W television. The fridge would get about 35 V, not enough to run, and the TV would have ~205 V, enough to destroy it.

If the LED lamp was on the same side of that hypothetical TV, and ground touched neutral, the lamp would get 120 V, rather than 35. However, it also means current is flowing through the ground wire, and possibly through the earth outside, making a shock hazard.

A bad connection or too heavy current load

If an appliance is using far to much current for the circuit, or if there is a bad connection to the neutral wire at the entrance panel, then there would be enough voltage drop in the neutral circuit to reduce power.

This is also bad, because it indicates a fire hazard.

It would be a good idea to check voltage at each outlet in the house, while appliances are plugged into the outlet and running. If voltages are significantly different between nominal 120 V outlets, or far from 120 VAC, have a licensed electrician determine the issue.

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  • I've tested a majority of outlets with different major appliances running and the biggest differences I got were 118 at one and 122 at another
    – Reese
    Mar 12 at 6:08
  • If the situation described in this answer is true, and I think so, you have a very dangerous situation. This can lead to personal injury and also fire, because you inevitably will have the ratings of some appliances exceeded. Get an expert to check this out.
    – Marcel
    Mar 12 at 10:30
  • @Reese, a 4 volt difference isn't terrible, but does indicate that voltage drop on the neutral. See greenbuildingadvisor.com/question/… for comment, "My guess is you have a loose connection somewhere, which is something that needs to be fixed." and further testing. Mar 12 at 13:28
  • @Marcel: Indeed, while local utilities may vary, the danger posed by a floating neutral is sufficient for many power companies to treat it as an emergency to which they will respond very promptly. Since the power company could be liable for harm caused by a broken neutral connection at the transformer, they will generally want to ensure as quickly as possible to ensure that there's no problem on their end.
    – supercat
    Mar 12 at 15:45

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