2

I'm trying to swap a light fixture. I'm used to a fairly standard 3 wire configuration (hot neutral ground) and this is what the replacement fixture expects. When I pulled off the old fixture, this is what I found: socket with 6 wires The two ground wires were twisted together and not connected to the ground from the old fixture. The two hot wires were twisted together and were not connected to the old fixture at all. The old lights ran between the two white wires.

I checked out the switch, it seems normal with just 3 wire attached where they should be: just 3 wires

I continuity tested everything and found the following (indicated by colors in the pictures):

  • The two copper wires are connected to the copper ground at the switch
  • One white wire is connected to ground
  • One is connected to the white neutral wire at the switch
  • Both black hot wires are connected to the black hot wire at the switch

I don't know for certain that black is actually hot and white is actually neutral, they could easily be reversed.

What should I do with this? My instinct is to cap off all the wires on the side where white and ground are shorted, and then just make a standard 3 wire connection using the other side. Would that be reasonable? Safe?

1 Answer 1

4

You have an (improperly done, outdated since the NEC 2011 code adoption in whatever your LAHJ is) switch loop.

The white at the switch (presently) is a switched hot, not a neutral.

A properly done switch loop (assuming it was, in fact, installed before the adoption of NEC 2011 in your area) would have the white from the switch joined to the black of the supply (constant hot) and remarked (tape, heat shrink, or paint/marker) black or red (I prefer red, it's more obviously intentional) or some other hot color to indicate that it's a white hot, not a neutral.

Then the black from the switch becomes a switched hot to the fixture. Neutral from the fixture connects to supply neutral (white). Fixture ground connects to the grounds (properly, with a wirenut or Wago, not just twisted and left.)

The current state of things will require identifying which side of the cable is supply. Since the ground is unbroken I assume they just clawed it open - so you need to undo the wirenut on the blacks and see which one is hot.

Having done that, you mark the white in the OTHER half of the cable (that leads to the switch - both here and at the switch) and connect black from the switch to the fixture, and white from the supply is the other white that was connected to the fixture (and should remain un-marked.)

Post NEC 2011 switch loops need /3 cable so that a neutral is supplied to the switch box, and then it's typical for red to be switched hot from the switch to the fixture.

1
  • Thank you for the explanation and detailed instructions! I followed what you said and the light works and the house isn't on fire so success!
    – Indigo
    Nov 15, 2023 at 5:59

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

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