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Yesterday my wife went through and replaced several receptacles and single pole switches. Most seem to be working fine, but now an entire breaker will not work (just the light fixtures, the outlets work). Interestingly, it is just switch controlled lights that aren’t working. Further, when I test the switches and the light fixtures themselves the tester trips indicating there is power, but the lights do not turn on. These are all ceiling lights I’m referring to. The outlets on the same breaker are working fine and power whatever I plug into them without issue - so it’s not like the breaker is blown or anything.

All of the switches are single pole so technically it shouldn’t be possible to wire them “incorrectly” as far as which screw receives which of the two wires. I’ve removed a few of the switches and confirmed the wiring is appropriate.

Is it best to just remove every single switch and ensure there isn’t anything loose? They are all individual so I wouldn’t think that one being “bad” would affect all ceiling lights on the same breaker, but I’m no expert.

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We have a "basics" Q&A on this. What usually gets people is "tabs".

But in this case, it seems like a neutral connection is having a bad day. So I would review neutral connections with great care.

Now you didn't mention anything about "accidents", but some people unaware of the hazard will do this work energized and get a flash-bang in the course of the work. Sometimes it trips the breaker and they go "Oh well, was meaning to do that". Other times it blows a "fuse" in a receptacle or switch.

Now, receptacles and switches aren't supposed to have fuses. This "fuse" characteristic is a side-effect of a cheap splicing technique called a "backstab", where wires are jabbed in holes and grabbed by little springs. Operative word, "little".

Backstabs are also features of only the cheapest outlets and switches - the better "spec grade" devices won't use backstabs but instead will support 2 wires per screw via a method described in the instructions.

Science recently found that screw torque is important, even on small terminals, and torque problems frequently result in burned up wire connections, and fires. As such, in 2014 Code was amended to require the use of a torque wrench or torque screwdriver to set the torque on any terminal which specifies one. This generally also requires combination bits (or flat and a steady hand), since the specified torque value is far too much for a Philips head.

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  • Thanks for the reply. The circuits were completely killed during the installation so I don’t think anything being blown is the issue. I’ll take off all the switches and review their wiring as well as the neutral wiring. The thing that I just can’t understand is how the light fixtures are receiving some element of power but not turning on. I assume that has something to do with current flow that I don’t understand.
    – Brett
    Sep 19, 2023 at 14:29
  • May have found the issue. There is one switch that only controls a single overhead light in an attic, but the switch box has 5 black and 5 neutrals coming into it. I can’t see this switch controlling anything else, and it isn’t a 3 pole because this light is not controlled by any other switch…
    – Brett
    Sep 19, 2023 at 15:05
  • @Brett that many wires are hard to get right in a wire nut, especially if you're using the wrong size nut, which people do A LOT. Consider 5-bay Wago lever-nuts. Sep 20, 2023 at 3:59
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Sometimes a mistake is done with ceiling light wiring.

Usually there is something called a switch loop. Means a white wire (like neutral) is use for switched hot and connected to the switch. That wire should have a black marker on it to identify it as such, but it might be overlooked or not there. If not connected the lights will not work.

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