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Remodeling my bathroom which, has now spilled into the hallway. I intend to leave the electrical configured the same as it has been so I drew up how it was wired before dismantling it. Only now, I'm not 100% sure I drew it up correctly in my notes as far as the hall lights and switch are configured.

See the attached diagram - Does the switch wiring to the hall lights make sense? enter image description herehttps://drive.google.com/file/d/1pdPZeA9_Oi-rYKF0LQrkVhmVpo4DmJJ2/view?usp=sharing

The line coming into hall light one is a shared neutral that branches off to an office, the switch and lights described have always been on the same circuit that is apart from the office

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  • Also, this was built and wired in 1957
    – Albert
    May 27, 2021 at 23:16
  • Was there only a single switch at the switch location, or was there a double switch there? May 27, 2021 at 23:23
  • It's only a single
    – Albert
    May 28, 2021 at 18:32

2 Answers 2

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I'm not an electrician, and I'm not familiar with the National Electrical Code, so this answer may contain inaccuracies.

Everything seems to make sense, but I see some potential problems.

In this diagram, all of the black wire nuts are always-hots. So are all of the black wires, except for the one coming from hall light #1. The white wire nuts in the upper boxes, and all of the wires connected to them, are neutrals. The white wire nut in the switch box, and all of the wires connected to it, are switched-hots. Each of the hall lights is connected to one switched-hot and one neutral, just like you want. All of the other cables exiting the diagram carry one always-hot and one neutral.

Here are the potential problems that I've noticed:

First, on hall light #1, the black wire is connected to neutral and the white wire is connected to switched-hot. It's probably supposed to be the other way around. If the light fixture has an Edison socket and it's wired the wrong way around, then the hot wire will be connected to the easy-to-touch part of the socket instead of the hard-to-touch part, which increases the risk of electrocution.

Second, the hot wires form a loop: the black wire in the upper left box connects to the switch box, where it connects to the upper right box, where it connects back to the upper left box. I believe that's a code violation, but I'm not able to find a source for that.

Third, the hot path and the neutral path for hall light #2 are different: the hot wire goes through the switch box, whereas the neutral wire goes through the cable that directly connects the two upper boxes. This will cause those wires to produce a stronger magnetic field than usual whenever those lights are turned on. If you have any audio equipment in your home, it may pick up that magnetic field and make an unpleasant noise (mains hum). If you don't have any audio equipment and you don't plan to get any, then mains hum won't be a problem for you. However, A. I. Breveleri pointed out in a comment on this answer that these magnetic fields can also cause inductive heating in nearby metal objects.

(When a wire carries a current, that wire will always produce a magnetic field. However, if you have two wires right next to each other carrying the same amount of current in opposite directions, then their magnetic fields will mostly cancel out. That's one of the reasons why hot and neutral wires are usually run right next to each other.)

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    The third issue you describe is a code violation even if you don't have any audio equipment and you don't plan to get any. The problem is that a hot or neutral with no balancing counter-current along the same path can cause inductive heating in nearby metal objects, along with the mains hum you mention. May 28, 2021 at 2:45
  • @A.I.Breveleri That's useful information, thanks! I've added a mention of that. May 28, 2021 at 3:32
  • Thanks for your help. In hindsight, there was a mild hum coming from an audio system for my computer in my office that seems to be gone ever since the breaker has been turned off.
    – Albert
    May 28, 2021 at 18:41
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Nope, this is a gory mess. I see what they were doing there, but they're not allowed to do that.

There's a bunch of paralleling going on, with multiple paths for the always-hot, and switched-hots going all directions from the switch.

There's no clean way to fix this, except to change out the switch for 2 switches, and make each light an independent "switch loop".

That way you sever the loop.

Another way of looking at it is, "power flow must go back the way it came". Or, in any cable, the currents in the wires must be equal and opposite, canceling each other out (or to be more precise, their electro-magnetic fields).

It should be noted that anytime white is used for "not a neutral", it must be used as the always-hot wire. In a separate rule, white can never be used for the switched-hot wire. So the "switch loops" will need to be rejiggered to make a re-marked white wire as the always-hot, and black as the switched-hot.

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  • Excellent. Thank you. Two switches it is
    – Albert
    May 28, 2021 at 18:47

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