2 different voltages in 3 way switch

16 years ago

I live in a 50s ranch house, and was replacing a 3 way switch on the inside of the house. Unfortunately, the original 3 way switch was not labelled as to which was the common terminal (no dark colored screw, no writing, nothing), so I took apart the switch, separated the wires, turned the electricity back on, and took voltage readings with my voltmeter. In one wire, I got a reading of 'normal' (approx 110-120 volts), and in another wire, I got a reading of approx 40 volts.... I've no idea why. In the third wire, there was no voltage.

So, I did some research on the web, and found a good article on 3 way switches. I began to think that the culprit may have been the accompanying 3 way switch (this one is in the garage), the one I had not touched yet. So, I took apart the switch, did voltage readings, and found that there was one hot wire coming into the switch.

I rechecked the three wires inside..... none were hot. Bingo, I thought, problem solved.... it must be a faulty switch. So, I put on a new 3 way switch in the garage..... connected the hot to the common, and the other two to the travellers.

Here's where it gets scary.....

I checked the voltages on the three bare wires inside..... one wire had approx normal voltage... 110-120. The other wire STILL HAD approx 40 volts, and the third wire, nothing.

I went out to the garage and flipped the 3 way switch out there, and when I dide that, I found that the voltages in the wires in the switch inside had REVERSED THEMSELVES! In other words, the wire that had shown 110-120 now showed 40, and the wire that had shown 40 now showed 110-120.

I double checked to make sure the new 3 way switch in the garage was wired correctly.... it was. Hot wire to the dark terminal screw labelled 'common.'

In the article I found, it said to find the common wire in the other switch, test the resistances. When I did, I got resistance in 2 wires, not one. I couldn't believe the outcome, so I did it again..... only this time there was a puff of smoke and my volt meter went 'Fffffffffft' and that was the end of it.

So, I'm left scratching my head, as to 'WTF is going on here anyway.' And why do I have 2 wires with voltage, when there should be only one?

My last guess..... and this is pretty desparate....but I'm thinking the wires in the light fixture maybe are reversed? i.e., the hot hooked up to the nuetral and vice versa?

Before I took apart the switch in the garage, but after I had hooked up the new 3 way switch inside, the light fixture would work, BUT ONLY IF THE SWITCH INSIDE WAS IN THE OFF POSITION. That's my only real clue to why I maybe should try to take apart the light fixture and see if reversing the wires would help any.

This is so unbelievably screwy, I can't believe it myself. I don't understand the two voltages, either.

Do I have a short somewhere? This is 50+ year old wiring, afterall.

Could the wires in the fixture maybe, possibly, be reversed?

Is this solvable? Or should I get an electrician?

Also...... I know that the wires are supposed to be properly color coded..... in this case, I don't think the color of the wires has anything to do with anything.... not sure those 'color conventions' were in use back in the mid 50s when this house was wired....

Many thanks in advance.......

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Comments (2)

itsunclebill
16 years ago
last modified: 9 years ago
No offence, but if you'd read a few posts you'd find out what you see (saw) is pretty normal. Of course, you didn't say what wire the other meter lead is hooked to get these voltages, but I'm guessing you found a neutral or ground.

So, if you get 120 volts on different travelers by moving the garage switch, things are wired right. No voltage on the third wire at the replaced switch would indicate this wire goes to the fixture, and to neutral through the lamp (bulb). The 40 volts you see is with a digital meter most likely. These meters read voltages with extremely small currents, in this case induced voltage from the hot traveler next to it. If you used a voltage tester like a Wiggy or an analog meter you wouldn't see any voltage on this wire.

Hook the two travelers (one will have the 120 volts, the other 40 - or whatever) to the brass screws, the fixture wire (no voltage) to the common, and put it together (with te power OFF PLEASE). If doing this resluts in the switch only working in one position, there's something else wrong - post back. If the light worked prior to the failure of the switch you were changing, why would you now assume all sorts of things, like wires being reversed, just sort of magically happened at the same time?

As to the meter, you NEVER EVER use the ohms or continuity functions while the power is on. If the meter is of any quality at all replacing a fuse may put it back in working order - - use ONLY the exact same type of fuse noted on the bad fuse, and make sure it is the same as noted on the meter.
boyd9
Original Author
16 years ago
last modified: 9 years ago
Thanks for your patience.....

I realized as I was going to bed last night that maybe everything was OK..... afterall, I DID have the switch working, just not the way I thought it should.

Now I realize, from more reading, that reversing the travelers would've reversed the 'on/off' of the switch..... in other words, I almost (prob) had it right the first time.....

It honestly hadn't occured to me that the lower voltage could be induced via proximity to the other wire.... makes perfect sense.

Again, many thanks.... sure I can get it from here.
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2 different voltages in 3 way switch

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itsunclebill

boyd9
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2 different voltages in 3 way switch

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itsunclebill

boyd9Original Author

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boyd9
Original Author