3 Switch Light Circuit - One Leg at 79% Lower Voltage - Cause For Concern?

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Baumgrenze

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Recently I restored to working the 3 switch light circuit that powers a single, utility incandescent bulb in the 2-car garage of our vintage 1955 tract home. We are the third owners and started our tenure in 1971.

I used this tutorial on my first try to restore all 3 switches to service. Despite the clear instructions I failed:

http://users.wfu.edu/matthews/misc/switches/4WayStills.html

Therefore I made a more methodical examination of the circuit.

The circuit, 3 switches (2 at the driveway doors and 1 at the house door,) predates 1971. I point this out because the 4-way switch is furthest from the 3-way switch at the garage/house door where the power is supplied.

I disconnected that switch and was troubled to discover there was a ~20% difference in the voltage to ground for the 2 hot leads, 1 black and 1 white, when the circuit was powered. The second black lead, a neutral, was at 0V to ground. The hot black lead read 96V and the white lead read 122V.

What might explain this difference? Should I be concerned about it? The light works as intended.

Thanks,
baumgrenze

Notes:

All of the original wiring is 12 gauge with ground in classic silver insulation.

This means that the line to the 4-way switch ran past the location of the other driveway 3-way and a second cable back across the garage was needed to install the second driveway switch. This was done when copper was very expensive and hard to obtain because of the Korean War effort.
 

Stuff

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Probably reading phantom voltage. The travelers run together and the powered wire causes the other to show voltage. Change to a analog meter as they are less sensitive to the phantom voltage.
 

Baumgrenze

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A 4 way switch does not have ANY hot leads. They are all travelers between the two switches.

I tried to keep the OP as brief as possible. "That switch" refers to the nearest noun, the 3-way switch where the power is supplied.

Probably reading phantom voltage. The travelers run together and the powered wire causes the other to show voltage. Change to a analog meter as they are less sensitive to the phantom voltage.

Are you suggesting this might be like the ~1 V reading I've often seen with circuits that include a lighted rocker switch?

I can see that there is opportunity for this to happen. The breaker that powers this light circuit also protects ceiling lights in the house that are nearby, some of which have lighted rocker switches and 3-switch controls, too.

I did not disconnect the wires to the remote 3-way and 4-way switches when I took the measurements the second time around so they probably created unpowered circuits.

Also, I did not completely unpack the 4x4 box where I worked. The wiring in it is more complex than I outlined. I did not want to complicate the original post. The box is a 1.5" deep 4x4 with a 1.5" stand-off ring and the switch cover stands proud adding volume. The box also holds a second switch on a different breaker. It controls fluorescent work lighting and a set of power receptacles in the shop area of the garage. The box is carefully marked to indicate that 2 breakers must be opened to remove all power from the box. Undoubtedly in the years since 1955 the code declared this an unacceptable practice.

Anyone who has done switch wiring with #12 wire knows that it is a PITA. It is also difficult to repack the switch box and every time this is done the copper wire work hardens a bit more and makes it more difficult to work with then and into the future.

Perhaps I should 'let sleeping dogs lie sleeping.' The lights work as intended. The circuit controls only one 150W incandescent bulb (for as long as they are available) so the load is small.

At a minimum perhaps I should recheck the voltages with my old analog Radio Shack meter, but days have a way of filling with other tasks...

Thanks
baumgrenze
 

Reach4

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Are you suggesting this might be like the ~1 V reading I've often seen with circuits that include a lighted rocker switch?
No. It's more like the 40 volts you might see between your fingers and other things when wearing rubber-bottom shoes and the humidity is lower.
 

Jadnashua

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What's probably more important would be to actually measure the voltage at the light fixture...if it is normal, you don't have a problem except in understanding what's happening (which would bug me, but I wouldn't lose sleep over it). IOW, if the lamp is a lot dimmer (lowered voltage) when operating with the switches in one position, then, you should figure out what's going on. If it isn't, don't worry about it.

FWIW, older switches can develop corrosion and burn marks on them, or lose tension on the spring contacts, which can become less than perfect switches. NOrmally, when that happens, you'd also notice that switch would get warm. If you have an IR thermometer, leave the lamp on for awhile and check each switch to see if it's temperature is rising. An IR camera can be useful, too, as it can spot the warming spots.
 

Baumgrenze

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What's probably more important would be to actually measure the voltage at the light fixture...if it is normal, you don't have a problem except in understanding what's happening (which would bug me, but I wouldn't lose sleep over it). IOW, if the lamp is a lot dimmer (lowered voltage) when operating with the switches in one position, then, you should figure out what's going on. If it isn't, don't worry about it.

FWIW, older switches can develop corrosion and burn marks on them, or lose tension on the spring contacts, which can become less than perfect switches. NOrmally, when that happens, you'd also notice that switch would get warm. If you have an IR thermometer, leave the lamp on for awhile and check each switch to see if it's temperature is rising. An IR camera can be useful, too, as it can spot the warming spots.

I believe I replaced all the switches with new ones earlier this year and was frustrated when they didn't do what I anticipated. I finally took time to revisit it all recently, just before posting my questions.

If I can find it, I should have an E26 light bulb socket to AC wall outlet plug adapter I can screw into the light socket. If I then plug in a short extension cord the setup will simplify reading the voltage at the socket. I will be careful to use my old Radio Shack analog meter to eliminate the problems inherent with digital VOM devices.

With apologies to King Solomon who taught us,

To everything there is a
(season, a time for every) purpose (under heaven). —Ecclesiastes 3:1.

We are encouraged to use the right tool for the job at hand.

thanks
baumgrenze
 

hj

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quote; "That switch" refers to the nearest noun, the 3-way switch where the power is supplied.

in that case there is only ONE hot wire, so I do not know what you are measuring for the "second" on.
 

Jadnashua

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You do not need neutral on any of those switches, and, except for where the power comes in, it may not be at any of them. Ground wires, though, should all be at the same potential, but that would depend on how well they are connected. Your best bet is to verify that the lamp itself is getting the proper voltage. ANy voltage measurements at a switch should be between one of the switch contacts and ground since there isn't likely a neutral there so don't take a white wire as being neutral.
 

Baumgrenze

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What's probably more important would be to actually measure the voltage at the light fixture...if it is normal, you don't have a problem except in understanding what's happening (which would bug me, but I wouldn't lose sleep over it).

As anticipated, using a screw-in socket and an extension cord I fairly quickly established that three switch combinations (up and down) gave me 120V AC at the socket and the other three gave me 0V.

As far as I am concerned, this is 'case closed.'

Thanks to all for participating.

baumgrenze
 
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