I'm installing a light fixture in my dining room and there is an existing wall box just below where I want to put the light switch. I'm assuming this old box also contained a switch. I was going to run the lines from the existing box through my switch and to the light. However, when I opened it up and pulled everything out, I was surprised to see that both black wires had been capped but the whites and grounds are still tied together.

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Does anyone know why the two hots would be capped and not tied together like the others?

  • 1
    Like you said... it was a switch. When they disabled it they wanted it turned off.
    – isherwood
    Oct 10 '18 at 22:55
  • Yea, that makes sense. It's just that nothing downstream of the switch would work anymore which is what I'm confused about because everything in the room seems to work fine.
    – bfink
    Oct 10 '18 at 23:06

That's exactly how it would be left if someone removed the switch. When the switch was there, the two blacks went to the switch, and the whites and grounds were spliced just like that and pushed into the back of the box.

After removing the switch, if they wanted to emulate the switch being on, they would have spliced the blacks together. If they wanted to emulate the switch being off, they'd do what they did.

That may be because they removed the fixture and did not want hot going somewhere it did not need to be.

  • Thanks, glad it's that easy. Seems like all I need to do is pull the hot up to my new switch box along with the neutral and ground. That seem like the right thing to do?
    – bfink
    Oct 11 '18 at 2:10
  • 1
    Went ahead and determined which wires went to the panel and wired up a new switch and it works great.
    – bfink
    Oct 11 '18 at 23:46

To understand what you have you should determine which of the two cables has the line hot and its associated neutral. Use a non-contact voltage tester or a standard voltmeter with probes.

At this point you could just ignore the extra cable (and maybe disconnect its neutral and cap it) and run a new cable from this box to the new box you want to install.

The other cable would have supplied power to a light or to a switched receptacle. Is there a ceiling box or a wall box for a light near this? Alternatively is there a receptacle near the switch (on the same wall or nearby on a perpendicular wall which is currently not working (check both of the receptacles of a duplex receptacle)? If all nearby receptacles are working, then you would have to look in them to see if there are capped off wires in them. Or look for unusual extra connections like jumpers from one receptacle to the other of the duplex receptacle.

Here is one possibility for how these wires came to be in this configuration:

There was a switch in this wall box which switched one half of a nearby duplex receptacle (so a floor or table lamp plugged in would be controlled by the wall switch). The other half of the duplex receptacle would have been powered by another cable and was always on.

If someone wanted both halves of the duplex receptacle always on, they would disconnect the wire from the switch and connect both receptacles to the always on power.


It is (most likely) an old Switch Loop

Switches are confusing until you have that "aha!" moment (which actually took me quite a while).

A switched fixture typically includes:

  • Grounds everywhere - connect them together, no reason to disconnect when removing the switch, so they are still connected.
  • Hot from the panel to the switch - that is one of the black wires.
  • Switched Hot from the switch to the fixture - that is the other black wire.
  • Neutrals - one from the panel to the switch and one from the switch to the fixture, so they are connected together.

However, older switches (and current switches that are "just switches" and not dimmers, smart switches, lighted switches, etc.) do not actually use the neutral. Sometimes you will not even find the neutral inside the switch box because it doesn't actually need to be there. Code now requires a neutral to allow for dimmers, smart switches, lighted switches, etc. so the configuration you found - neutral from fixture and neutral from panel connected together - is perfectly normal. If you need neutral for your new switch, pigtail it to the existing neutrals.

So why aren't the blacks connected? Because that would complete the circuit. If a fixture is still in place then it would always be on. The gap between the two blacks is equivalent to an "off" switch.

As others (especially Harper) often point out, a black switched hot is a convenience (NM cable is normally black + white + ground) but is confusing, so labeling it by putting red electrical tape on both ends (in the switch box and at the fixture) avoids confusion. But most of the time it is just another confusing black wire.

The one important thing to figure out is "which black is hot and which one is switched hot". That is actually easy: Using a non-contact tester with the circuit breaker ON, the "hot" black will be live and the "switched hot" going to the fixture will not be live.

  • Thanks for the thorough write up. I understand the "always on" aspect, but what I'm missing is that there doesn't seem to be anything "always off" (due to the missing switch). However, this is a very old house, so the fixture could have been removed, hidden, etc. Sounds like what I need to do is determine which black is hot and run that to my new switch and ignore the switched hot from the old box - seem reasonable?
    – bfink
    Oct 10 '18 at 23:38
  • 1
    switch loops are cool. But here, power is supplied at the switch. That is not a switch loop. Oct 11 '18 at 1:45
  • @Harper - Looks like I got the description (I hope, I think...) of the wiring correct, but not the term. I just Google'd and apparently switch loop is (if I found the right answer) for MULTIPLE lights. So what is an "ordinary", "single fixture" - hot -> switched hot -> neutral circuit like this officially called? Oct 11 '18 at 1:58
  • @bfink You need to figure out which white & black go to the panel and which ones to the old switched location. Then connect the "to the panel" white (neutral) and black (hot) to a new cable going to your new switch location. The old neutral and switched hot are then junk - but it would be preferable to actually know where they are going - worst case you can cap them with wire nuts in this box to keep things safe. Then in the new switch box you run a switched hot (typically black but Harper recommends marking both ends of it red so you know what it is later)/neutral (white) to the fixture. Oct 11 '18 at 3:01
  • Perfect, that's exactly what I planned on doing. Thanks!!
    – bfink
    Oct 11 '18 at 3:03

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