I am restoring an old house and have completely rewired it. I have one circuit that does not seem quite right (all others — over 40 circuits — work properly and have the correct voltages.) This circuit is a three-way switch circuit controlling a light. The light is in line prior to the two three way switches. I am quite certain I have wired the circuits properly. As with all my circuits, I check the voltages. On this circuit, I measure 120 volts when the switches are “on”. However, when the switches are “off”, I measure about 30 volts. My system has two panel (one where the main service enters and another in the center of the house as a sub panel.) The circuit in question is on the sub panel. I was originally concerned that I was experiencing a bias voltage because of grounding (the sub panel is about 70′ from the main panel) so I installed a grounding rod circuit to the sub panel also (of course the main panel is also grounded with a grounding rod.) The sub panel grounding did not help. I then turned off all breakers in both panels (except the three-way switch circuit breaker) and checked the voltages again. I still measure about 30 volts in the off position.
My question: does anyone know why I am getting this 30 volt reading on the three way circuit?
Thanks,
Harold
Replies
Are you measuring at the panel, switch or fixture? If you measure after the fixture but between the first switch you may be measuring a voltage drop through the fixture. Try taking the bulb out, this should break the circuit and you should get zero volts on the switch side of the fixture and 120 on the supply side.
Treefreak: I have not yet installed any fixture. I am measuring across the two legs (supply and return) of the wires that would normally connect to the fixture.
Harold
I'm not sure how turning the switches on or off would effect the voltage if there is not a load in the circuit. If I understand 3-way circuits right, the light fixture would be in front of the switches with neutral passing through the light and hot being wired direct to the first switch. If this is the case the switches should have no effect at all when measuring between hot and neutral at the fixture (w/o a bulb).
Hi TF,What's the possibility that your polarity has been crossed (fairly common in old buildings). You could be getting some stray voltage from the neutral side if someone messed up sometime in the past.TomIf you can get your hnds on a signal tracer, it might help you find your leak.
Edited 2/17/2005 12:16 pm ET by tms
You sound as though your are very knowlegeable about all this.
If you don't get an answer to the problem here, you might try Breaktime; they have quite a few licensed electricians over there. Just don't call them "sparkies".
Nikkiwood:
Thanks for the suggestion. I will post it on Breaktime.
Harold
There's a number of good dedicated electrical forums. Don't have my list handy on this puter but a quick google will turn up a bunch of them. I recall seeing that question asked on a few of them so the answer is waiting for you.
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