Lighting wiring question

[Max]

Here's a very rough drawing of the wiring inside one of the switch boxes in my basement:


Please note that I have left out the earth wires and the return wires are shown as blue instead of white for clarity.

A green "dot" on a switch means the terminal is always hot and a half green dot means that the terminal is only hot when the switch is closed.

You will see there are two terminals, one on each switch, that are never hot regardless of the position of the switch, is this correct for a 3-way switching circuit? This is the way the wiring was when we moved into the house last year. The basement light can be switched from two switches.

Now, for the outside light. The whole reason I am digging around in the switch box in the first place is because our outside lights used to work and then stopped for no apparent reason. The bulbs are fine and I am registering a voltage on the switch terminals but when I click the switch...no light. I can't examine the wiring between the switch and the lights because it is all hidden above the ceiling. I know this isn't a breaker issue because there is power on the switch, is it possible that mice could have chewed through the wire? Another question. If the wiring looks like a 3-way switch then that begs the question, where is the other switch? (We don't know). Is it possible that there could be a problem with the other switch that would stop the outsise lights from working? We have one unidentified switch in our foyer that the previous owner had taped in the on position which we found suspicious. So many unknowns. Might as well mention that all the wiring that I've looked at so far seems to employ back-stabbing which doesn't fill me with much confidence. We're probably going to get an electrician in to have a look a this, and other issues, I just wanted to see if anyone had any ideas that I could try in the meantime.

TIA, Max

[kactuskid]

The dark colored screws on your three way switches are called common screws. These common screws will have the incomming power wire connected to it, and the common screw on the other 3way switch will have the light fixture fed from it. So be sure to put a piece of tape or label on this wire before removing the switch. If you can't find the other 3 way switch (and I would try looking in the garage for it). What I would suggest you do is replace this 3 way switch with a new one. This is easy to do, cheap, and if it fix's it you don't need an electrician. Just be sure to open the breaker first. Here's a link that shows how 3ways operatehttp://www.danswiringpage.com/3ways_101.htm\ Also remove any wires that are inserted in the backstabbed little holes and wrap them around the screws on the sides. These holes are notorious for bad connections.

[Max]

Thanks for the info!

One thing I neglected to mention is that I fitted a piece of plyboard around the box because my wife complained about reaching for the switch in the dark and shoving her hand in the insulation (the basement is unfinished you see). I nailed the board in place so I thought there might be a chance that I shook a wire loose. When I saw that all the wires were intact and that I measured a voltage across the screws I thought all was well. BUT, you say "These holes are notorious for bad connections." so perhaps even though the wire looks like it is in place it might not be making a connection. Hmmmm. I will rewire the light switch (if not replace it) and try again. I guess every time I find a backstabbed receptacle I should take the time to fix it.

Thanks again!

[kactuskid]

You very well could of loosened one of the wires. Here's a link to show some details on backstabbing

http://www.thisoldhouse.com/toh/knowhow/electrical/article/0,16417,562098-9,00.html#

If you find any of your switches or receptacles backstabbed then fix them cause it'll be just a matter of time before you have a problem with them too.

Don't forget to lable the wire that goes to the dark colored screw on your switch (the common screw) before you replace it. Your new switch may not have the common screw located in the same place and then you'll have another problem in trying to figure it out. Good luck and let me know how it goes.

[Max]

Yes, I will remember to mark the wire, always a good practice. Since this is a relatively easy job I'll do it when I get home and see what happens. I'll let you know.

Cheers, Max

[Max]

Hmmmmmmmm, I didn't do the job yet because the first thing I found was that the wire attached to the dark screw is not the hot wire, it only registers a voltage when the switch is closed. I don't know if this means it's incorrectly wired but I decided to leave it for now.

[Kodiak]

on a 3-way switch the common is always in contact with 1 of the other 2 terminals, which one depends on position of switch.If you always have power at one of the travelers on the second switch (assuming the other switch has not been flippede)it should mean power is fed into the other 3-way(common screw) getting to your second 3-way via the 2- travelers, and that common should be connected to your light. If you have power at the common the light should work unless something is broken between the 2nd switch and the light. I would check if you have power at the light, hot to neutral and hot to ground, because you may be loosing the neutral and not the hot leg.

[Max]

Thanks Kodia. I was thinking that it doesn't have to be the hot wire that is disconnected somewhere. I'm gonna leave it for now as I'm back off home to Scotland for a couple of weeks.

On some unrelated but good news, I fixed the problem we had with lack of power in out kitchen, the GFCI receptacle had been tugged a little too hard by our granite countertop fitters and the hot wire had popped out the back so I re-attached it properly. I'm glad we didn't get an electrician out now since it was such an easy job.

Thanks for the advice guys 'n' gals, there forums are a wealth of information. I just wish I had found them earlier and it would be great if there was some nugget of useful information I could give back. Maybe in time.