My daughter in law called because she had tried to replace an ugly ceiling fan and light fixture with a light only fixture and whenever she threw the wall switch it tripped the breaker. I thought it would be easy to figure out but not so.
The old fixture (which she had already removed) was controlled by two light switches and a variable speed fan control. The light switches are at each end of the room – so a three way circuit is in place and the fan control is boxed in a two gang with one of the toggle light switches.
The ceiling fixture has a black, red, white and ground. The red is always hot regardless of how the switches or fan control are set. I even removed the fan rheostat completely and capped off the wires in the wall. Red was still hot regardless of the toggle switch positions. The black wire is hot when the wall switches are on. The white is never hot. When I wire a simple light load across the black and white wires, turn on the wall switch, the black is no longer hot and the light doesn't work.
I can't understand how this could ever have worked. There seems to be no connection between the fan control on the wall and the ceiling fixture. Why does hooking up the light between black and white kill the power entirely. Nothing seems to switch off the red!! Arrggh. Any ideas anyone? Any other tests I can run on the setup which may throw light on what is happening?
Best Answer
When someone does a light fixture replacement with switches involved and has a problem, it is usually because they reconnected the white wire that feeds power to a switch back to the other whites thinking it is a neutral.
Then they connect the black to the hot feed throw the switch and it trips the breaker because it is now a dead short.
When using cable to feed switches and return a switch leg, the proper practice is to feed the white wire hot to the switch and return the black wire to the light from the switch. Then (and this is the part many people don't do) you are supposed to re-identify the white wire as some other color. Black tape or red paint or something permanent. I like to use blue tape since you don't see blue in residential wiring. This show the next person that this wire is a switch feed NOT a neutral.
Sounds like the red is a hot feed from the panel that powers the whole circuit. If you are testing for "hot" with a no-contact tester you can get false positives that are from induced currents. You need a basic electrician's voltage tester.
You may have to take all the wiring apart and methodically identify each cable and conductor. Then plan how to reconnect the wiring to accomplish your goal.
Good luck!