We have a problem where a light in the stairwell is controlled by 2 - 3way switches, however not in the traditional sense. When you turn the light on with one switch, you have to turn it back off with the same switch. It can be either one, but it must be the same one to turn on and back off.
I've rewired the entire circuit. (I'm an industrial controls electrician.) With no power on the circuit, I checked the resistance through the switches. The circuit performs perfectly. When I apply power, we have the same issue.
I removed the light fixture and inserted the voltmeter between the power coming back from the switch to the fixture (hot). I tie the other lead of the meter to the neutral of the power coming in. Theoretically I should see 0 volts (or very close) when the switches are in one position, and then changing to 120 volts and back, but I don't. I see 120 volts and as I switch one or another switch it goes to 105 volts or 110 volts.
I'm not entirely sure what I have on my hands here. I have only 2 wires (old) power coming into the new circuit I've replaced, so there is no ground to check to. I'm thinking someone might have crossed the wires and I may be switching neutral?
I'm not sure. I guess I will be re-wiring the rest of the incoming circuit as well. :-(
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One of the two switches has the power coming in with no ground. It would be good to run a ground.
This switch has the hot wire connected to it (or possibly the neutral if someone crossed the wires). The two wires coming off the switch on a three way will always have one wire hot and one not. These are the "travellers". You can use your meter to measure the voltage between a traveller and the neutral to make sure the switch is working correctly. The hot traveller will change with switch position.
The second switch should receive the two travellers from the first switch. The output wire from the second switch, called the switch leg, goes to the light. You can use your meter to make sure that one traveller is hot from the other switch, then throw the other switch and make sure the other traveller is hot.
The neutral should be continuous through all this and its voltage to any ground (water line, drain line, furnace duct) should be zero.
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