Correcting a "misbehaving" 3-way switch

May 21, 2005 3 Replies

Rate this thread:

deja_bhoot2000 21 years ago

The foyer in my house has two lights about 1/4 away from each end, and there are two switches at either end. Something like the following:

Switch A Light 1 Light 2 Switch B

Switches A & B control lights 1 & 2 in the following way:

Switch position Result Comment A_up, B_up Both lights on ==> lights 1 & 2 are in parallel A_down, B_up Both lights off As expected A_up, B_down Both lights off As expected A_down, B_down Both lights OFF THIS IS THE PROBLEM

It is the 4th case (A_down, B_Down) that is baffling me. In a regular

3-way switch, the lights should come on. In effect, my 3-way switch behaves like a "2.5-way switch, so to say". These two switches have ALWAYS behaved like this for last 6 years, since I bought the house (but the seller may have redone these, since switches look different than all other switches in the house).

I would greatly appreciate your advice and suggestions on the following.

Q1. Does this indicate a problem at Switch A? Or Switch B? Both?

Q2. Can this be rectified by opening the switch boxes?

Q3. I have a tester and have done the following electrical work in the past, without any problems: replace house fuse; replace the outlet box for the 200 V (dryer); extend the power line and add a motion detector light to the outside of the garage. Should I attempt to rectify the

3-way switch myself, or should I pay an electrician? (Seems silly to pay $75, minimum for the visit, to rectify such a simple problem).

Thanks a lot.

Bhoot Nath

Vote

Robert Barr 21 years ago

It is a simple problem. Assuming the circuit ever worked properly to begin with, you'll have this behavior if the traveler has been swapped with the 'hot' terminal on either switch.

Sketch it out and you'll see.

It's far too much of a headache to try to trace down what went wrong where. There are too many possible combinations.

The way to go is to disconnect the power, remove all the wires (don't panic) from both switches (6 total) and go at them with an ohmmeter or continuity checker. You can use a long piece of wire or an extension cord as a really long meter lead and find which pair of wires have continuity between both switch locations. 2 wires will have continuity. You've found the travelers. Take if trom there.

Vote

Jeff Wisnia 21 years ago

I concur. I'd suggest that you first look at a diagram of how two switches control one (or in your case two) lights to understand how a pair of three way switches do their job. Try this one:

formatting link

The second light in your foyer has to be connected in parallel with the first one. i.e. "across it".

It is possible that the wiring IS presently going to the correct switch terminals but one of the switches has become defective so that its "arm" doesn't connect to one of its two stationary contacts when it should. That will produce the fault you describe.

Failing that, you'll have to learn how to "ring out" the wiring as Robert says, or see if you can dope it out from the wire colors and a diagram like the one above.

Above all, BE CAREFUL!

HTH,

Jeff

Vote

Doug Miller 21 years ago

Did you read my responses yesterday in misc.consumers.house ?

That it has *always* been like this suggests very strongly that at least one of the switches is a standard two-way switch. Have you actually verified that they really *are* three-ways?

-- Regards, Doug Miller (alphageek at milmac dot com)

Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?

Vote

Join the Discussion

Have something to add? Share your thoughts — no account required.

Didn't find your answer?

Ask the community — no account required