Unexpected Voltage

[H_Gonzales]

Hi all,

I encountered something unexpected in the basement wiring that I am hoping that someone can shed some light on for me.

Essentially my question relates to a voltage reading taken from a light fixture with the switch off. I would assume that with the switch in the off position, it would read 0 V on a multimeter.

With the switch off, I get approximately 25 Volts on the meter. with the switch on, it jumps to 120, right where I would expect it.

I have two sets of two lights ( total of four lights ). Each set of light is controlled by a switch (two switches).

The box in the rafters has the following wires in it:

1 - To Set of fixtures #1
2 - To Set of fixtures #2
3 - To Switch #1
4 - To Switch #2
5 - Feed from Circuit Breaker

All of the white wires are tied together in this box (From #1, #2 and #5 above). The Black wire goes through the switch and then to the fixture (Black #5, tied to Black #3, Black #4). The opposite side of the switch is tied to the Black on the associated fixtures.


My question, is why does the fixture have over 20 volts when the switch is off? I am a bit confused.

Thanks for your help.

HG

[Tom L.]

First off, If you are using a digital meter, try a new battery in it. Ive seen meters do weird stuff like that (voltage is off in certain ranges only) when the battery gets low....even if your battery light is off.
IF it is a analog meter, check the calibration. Now with the simple stuff out of the way..

If there was that much voltage after the switch I would think there would be arcing and heat generated. Ive seen breakers let .000000000001 - 3 volts through but never any more.

What kind of lights? I cant think of any type of lights that would have a capicator in it that could be back feeding voltage... mabye a floressent. (starter?)

COmpletely unhook the switch and see if you still have it.. IF it goes away try a new switch. If its still there start unhooking light fixtures one at a time. If its a floressent light, i dont konw if i'd really consider it a problem if everything is workign correctly. It may be somethign bleeding down.

[H_Gonzales]

Thanks for the response.
If you are using a digital meter, try a new battery in it.
I will try a new battery in my meter (digital).

COmpletely unhook the switch and see if you still have it..
On the switch, I have previously completely removed the switch (thinking that the voltage was "leaking" through) and the ~25 volts remained.

What kind of lights?
The typical incandescent lights were removed to just bare wires (fixtures and all removed) again, the same phenomena remained.

An associate suggested I try turning off each non related breaker one at a time to determine if an unbalanced load is backfeeding through the neutral. I will give that a try also.

I appreciate the help and suggestions. Thanks.

HG

[Wgoodrich]

What you are reading is current flowing from other loads on the electrical system using that same white wire as a return path [aka neutral] back to the transformer. While this is not truly proper it is what I call dirty wiring in dwellings where people wire nutted all white wires in junction boxes or multigang switch boxes that had more than one branch circuit in that box. Teh white wires have been intertied between different branch circuits. This will read anywhere from 5 volts to 50 volts on a white wire. This voltage reading is present regardless what you do with those light fixtures or switches on that certain switch system.

To prove what I am saying disconnect the white wire going as power out white to the rest of the branch circuit so that no white wire is connected in that switch system or light fixtures of that switch system. Either the whte power out going to hte rest of the branch circuit is disconnnected killing the rest of that branch circuit or you will still read the voltage reading even with all wires disconnected in all those 4 light fixtures and the switches for those light fixtures. The voltage is present on the white throughout the entire branch circuit often even when you shut off the braeker that runs those lights. This is because white wires from different branch circuits are interconnected mixing those white wires with other branch circuits. Only way to solve that voltage on the white would be to open every box in the house and separate the white wires so that the white wires of only that certain branch circuit is connected together.

Now you should understand when you see me comment that dwelling wiring is often the dirtiest wiring in the electrical industry. Over time all the white wires of all the branch circuits in the same boxes with any other branch circuit is interconnected.

Many times we get reports where two hot wires of two branch circuits in sync with each other. People often do this without realizing they did this intermixing of even hot wires of different branch circuits until the shut off a single pole breaker and find that two single pole breakers serve power to the same light fixture and both breakers would have to be shut off to kill that one light fixture. Then they realize someone intermixed even the hot wires in dwellings. This is a by product of lack of skill of do it yourselfers that didn't realize they did it themselves. Maybe as time goes by and the more we talk on these forums the more people will realize what to watch out for when they wire there projects.

Until that time you will find what you are finding. My educated opinion on the subject is you have intermixed white wires of different branch circuits providing your voltage or you have a power out cable feeding power further downstream of that same branch circuit that has a white wire carrying current from that same branch circuit under load downstream back to the panel.

Hope this helps

Wg

[H_Gonzales]

After some investigation, I found (and corrected) the problem.

The misc. voltage was not due to the intermixing of commons. The wiring of the switch was using two conductors in one wire. When the switch was open, the close proximity caused me the odd voltage.

Once the switch wire was replaced with 3 conductor (white, black, bare) wire and the bare wire connected to the others, the odd voltage when the switch was open, went away.

Best Regards,

HG

[Wgoodrich]

I am glad you feel that you sloved your problem. It is a common problem. Not proper but commonly found stray voltage.

However in my opinion you did not get rid of that stray voltage you just moved it down stream to a different location where the resistance reaches the right level in your white conductors.

When you added the white grounded leg in that box you created a strong enough path to move that voltage lower to a non readable level because your reduced resitance in your grounded leg in that box.

However if you checked you will still find more than one branch circuit on the same white wires intermixing the white wires of two or more branch circuits together.

Not saying you are unsafe or safe. Just saying your white wires are intermixed amoung other white wires of other branch circuits as I explained before. If you want to confirm that I am wrong then go to a nearby double, triple or four gang switch box that has more than one branch circuit in that switch box and separate all the white wires. Write down all that quites working. Be careful these white wires disconnected and loaded is a drastic shock hazard. Once you have documented all that quite working turn all breakers off in the panel. Then turn one breaker at a time until you find those items you listed to start working again. Make sure all other breakers but that one breaker that energizes those that you listed. Then go over you list and I suspect you will find some on that list still not working being fed from a second branch circuit breaker. Then remember you connected all the white wires in that multigang switch box under one wire nut and also remember you had more than one branch circuit in that switch box before you started.

What you had was not edy currents but rather white wires intermixed between two branch circuits. When you added the new white grounded leg you just reduced the resistance on the white wires in that certain switch box thus moving that unbalanced stray voltage to a different location in the home where again resistance is high compared to the current being carried on that white wires.

Good Luck and hope to see you on your next project.

Wg