Can changing the light switch do this?

[marinajc]

Hi:

We have a hallway with a three way circuit and two lights. My husband changed one of the light switches and now the synchronization doesn't work between them. By this I mean that or both of the light switches won't turn the lights on unless you turn the other switch off or on first. Any ideas why just changing a light switch would make this happen?

Thanks.

 

[breezer]

wrong type of switch, incorectly wired

 

[marinajc]

Thanks. I know you don't have much information from me, but can you please be more specific? All he did was change the switch at one end. It worked fine before that. Thanks for your advice.

 

[yankey-sparky]

Well first thing's first. Are you certain the old 3-way switch was replaced with a new 3-way switch, or could it have been replaced with a regular switch by mistake?

There are several mistakes that could have been made. It would help if you told us what the four possible up/down combinations do, for example in a correctly wired system:
A up B up - OFF
A up B down - ON
A down B up - ON
A down B down - OFF

How do your combinations behave?

 

[marinajc]

You mean there is a 3 way switch and regular switch? We must have used a regular switch then?

 

[yankey-sparky]

Looks like we found our problem.
Your friendly and helpful sales associate at your local hardware store will gladly explain the difference, help you select the right switch, and instruct you on how to fix your mistake. Small, family-owned hardware stores will be the most help.

If you search for "3 way switch" on the internet you'll find wiring diagrams and additional help.

 

[marinajc]

But if it's simply the switch I'm changing, I don't need diagrams for wiring do I?

 

[yankey-sparky]

Okay, here's the long answer.

A normal switch is what we call "single pole single throw", or SPST. This means that in one position, the switch makes a contact between wire 1 and wire 2, and in the other position, the switch breaks the contact between wire 1 and wire 2. When wired in series, either switch can turn OFF the light, but BOTH switches have to be on to turn ON the light.
A up B up = ON
A up B down = OFF
A down B up = OFF
A down B down = OFF

A three way switch is a "single pole double throw", or SPDT, switch. This means that in one position, the switch makes a contact between wires 1 and 2, and in the other position the switch makes contact between wires 1 and 3. If you hook two of these switches up in series, you get:
A up B up = OFF
A up B down = ON
A down B up = ON
A down B down = OFF

But you have to know how to hook them up correctly. See this link for more information.

 

[johnashworth]

_____________________________
lynda, moderator

its very nice of you to reply, but as the post is 2 1/2 years old I do not think the OP will be worrying about it now