Electrical – How to install a light socket in the middle of a power line with a switch

electricallight-fixtureswitch

I am replacing a light fixture in the middle of a circuit. Power flows into the fixture from the circuit breaker and out of the fixture to other lights and whatnot. There's also a switch attached. I thought I hooked everything back together properly, but when I switched the circuit back on at the breaker, the light turned on even though the switch was off. When I turned the switch on, it tripped the circuit. I attempted to make a diagram (minus grounding wires which are also connected). What did I do wrong and how do I fix it?

My awesome diagram

Best Answer

You put the switch and the light fixture both between hot & neutral, effectively parallel to each other. That makes the light always on and the switch creates a short between hot & neutral - correctly tripping the breaker.

What you have is a switch loop. They are confusing at first but actually quite simple.

Light switches are normally wired in the "middle" of the hot wire between the power source and the light. The way you do that with a switch loop is as follows:

  • Black from power (hot) connects (yes this will seem strange) to the white wire going to the switch. It bypasses the light fixture.
  • White from power (neutral) connects to the silver screw on the light fixture.
  • Black from the switch goes to the brass screw on the light fixture. This is called switched hot.

This uses the same wires you already have, just arranged slightly differently. Plus you need one more wire nut to connect the black power wire to the white switch wire.

In order to avoid future confusion, you should put colored electrical tape (not green or white) near both ends of that white switch loop wire to indicate that it is a hot wire. fixed light switch

As noted in a comment on the question, you may want to preemptively replace the switch as it may have been damaged by arcing from shorting. If you do that (or if you replace it sometime later for any other reason), keep in mind that a traditional switch loop does not have neutral. That rules out many, but not all, options for timers, lighted switches, dimmers, smart switches, etc. If you put in anything other than a simple switch, make sure that it does not require neutral.