Weird Electrical - 7 Volts when Off

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Old 04-10-20, 02:57 PM
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Question Weird Electrical - 7 Volts when Off

My basement has one room running the entire length of the house. There is one light controlled by a switch upstairs and 2 additional 'wing lights', each with 2 light bulbs in, controlled by two switches at the bottom of the stairs.

The home was wired by an idiot in the late 50s or early 60s, hence no grounding. There have been problems with one or the other wing lights being left on, sometimes all night long. My solution to this was simple - wire an outlet at the bottom of the stairs that would be visible from the top and plug in an LED nightlight to each plug, breaking out the separator tab to make each plug independent. When a wing light is turned on, the night light goes on and is a reminder to turn it off. We can also see the night lights plainly from upstairs at a glance.

One side went swimmingly. I discovered that instead of the power going to the switch first and then out to the light, it went to the light and then back to the switch. (This is backwards from how I've seen other lights wired & how I was taught to wire a switched light.) The two blacks are wired together in the light fixture and the white returning from the switch is the switched 'hot'. I pig-tailed the switched hot to one plug on the outlet. Because there was no return available, I ran a romex from a nearby outlet to the new outlet, only using the white wire to provide a path back to the breaker box. Everything tested perfectly and it works exactly as intended.

The left side went similarly, though I found when I was testing that when the switch was off, there was 7 or 8 volts AC between the switched hot & the return. Figuring it was just a bad switch, I replaced it and finished up. Last night, I saw a dim glow from the left night light... what the?!??? Testing revealed this same 7 to 8 volt AC between the return & the switched hot when the switch is off.

Disconnecting the wire from the switch revealed that the problem is not with the switch - the low voltage is there even with the switched hot disconnected from the switch, so it must be somehow feeding back from the light fixture itself! Further testing showed that the voltage ONLY exists when an LED bulb is in one or both of the light sockets! Having an incandescent bulb in eliminates the problem; have to assume that the bulb is using the power and the filament in the bulb is just not getting hot enough to generate detectable light/heat. (This theory would explain why bulbs in this particular fixture have always burnt out faster than any others when incandescents were in use.)

I replaced all the wiring in the light fixture - the guy who wired it used lamp cord & those crush-style barrel connectors like you'd use in a car/boat! - with 14 gauge solid wire pulled from a romex. Same problem.

Then I eliminated the light fixture itself by wiring an outlet to the switched hot where it comes into the light fixture and the return from the light fixture. Everything is fine - 0 volts when the switch is off - but when I connect a desk lamp to it and turn it on, essentially relying on the wall switch to turn the light on/off, the same 7 to 8 volt AC returns when the switch is in the off position and light is off. Thinking it might be from an appliance somehow, I unplugged everything else on the circuit, but the 7 - 8 volt AC remains.

Frankly, I am at a loss as to what is causing this or even how to proceed. I'd rather not have to re-wire the light fixture as it's above a ceiling that would have to be cut out, but don't even have any theories as to what might be causing it. I've never run into a situation where there's partial voltage present before - usually, there's either 110 or there is 0. I'm fairly certain that this problem has existed for years and I just now discovered it because of the night light, but would like to correct it if possible.

Any help/advice/ideas would be appreciated.
 
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Old 04-10-20, 06:54 PM
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First off the switch loop is miswired. The white should be the feed to the switch, not the return. The other issue is all conductors need to be in the same cable. You cannot grab from other circuits for the neutral.

The voltage sounds like phantom voltage.
 
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Old 04-10-20, 08:36 PM
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I can easily change which conductor feeds the switch & which is the return, but don't see what difference that will make. Same thing with the return; they're all wired to the same bar in the breaker box, so it's not like the breaker is going to cut connectivity to the white, even if turned off.

Would phantom/induced voltage be enough to power a night light like this??? (I've read several articles on it, but much of it is over my head.) Seems very odd that one fixture/switch has the problem & another on the same circuit wired the same way does not...
 
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Old 04-11-20, 05:37 AM
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I've had phantom voltage like this in 3 way switches when the travelers are not connected correctly. Is it a 3 way? I couldn't tell from your description of upstairs downstairs.

Btw, is fairly common in old houses to have the power go to the light first instead of the switch.
 
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Old 04-11-20, 05:49 AM
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The problem with the miswired switch loop is you now have two whites at the fixture. This could lead to the screw shell being the hot and creating a shock hazard. It is also a code violation.
 
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Old 04-11-20, 08:57 AM
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Sorry for not being clear @qwertyjjj - they are all single-pole switches. (I probably shouldn't have even included the part about there being an upstairs switch controlling the other light downstairs as it has nothing to do with this issue... such a thing as being overly-detailed & I routinely stray into that territory.)

Thanks for the info about it being common to be wired to the light first... it's annoying to me, but at least I know it was considered OK back then. It's still annoying though, as there's no return to use to add another switched device in the switch box - maybe that's why the standard way of wiring it was changed?


I changed the wiring as you suggested @pcboss , but it made no difference; apart from the wire colors being different, it's the exact same as it was with nothing hot that wasn't hot before. (Instead of having incoming black wired to black going out to the switch and white from the switch being wired to the blacks to the bulbs, the incoming black is wired to the white going out to the switch and black from the switch is wired to the blacks going to the bulbs.) No functional difference & the low voltage is still there when the switch is off.
 
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Old 04-11-20, 11:21 AM
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The home was wired by an idiot in the late 50s or early 60s, hence no grounding.
Most likely the wiring met code at the time, a ground wire hasn't always been required. That is why many years ago it was quite common to see 14-2 and 12-2 NM cable with no grounding conductor.
 
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Old 04-15-20, 10:45 AM
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Non-grounded romex did meet code at the time the house was wired, but I stand by my statement that the house was wired by an idiot. (Somehow, I doubt that using brown lamp wire, cloth electrical tape, or 12 volt barrel connectors for house wiring were ever acceptable.) My father knew the guy who built/wired the house & he would do anything to save a dime. Inspector in the town back then would accept a case of beer and the person saying it's good to give his approval. A couple years after my dad first bought the house, he had an electrical problem & looked in the fuse box - instead of fuses, there were 4 pennies jammed into each fuse receptacle!



I've done a bunch more troubleshooting and am even more perplexed.

The switch/light is on circuit #1 in my house. If breaker #1 is turned off, the low voltage immediately disappears. To me, this would eliminate the possibility of voltage being induced by the romex being too near another energized wire, but I removed all the staples holding the cable to the wall & moved it away from the 220 line powering the stove. There was no impact on the low voltage when the switch is off.

To eliminate anything else on the circuit from causing problems, I disconnected the romex from the washer, dryer, fruit cellar, and north wing lights; the low voltage is still there. I went through the house several years ago and mapped out everything on each of the 24 breakers, one by one; I know of nothing unaccounted for and of nothing else on circuit #1. There must be at least one junction box that I cannot access though - there is a single wire connected to breaker #1 & it's not pigtailed in the box. Each wing light and the fruit cellar light are end-points and nothing is fed out from them. The washer outlet is fed from the dryer outlet, but nothing is fed out from there.

At a loss of what else to try, I cut the end off of an extension cord and used this to temporarily bypass the different segments of romex in the house. First, I wired a brand new switch (which I tested first) to it and changed the wiring in the light fixture to eliminate the house wiring from the light to the switch - the low voltage was still there, though instead of 7-8 volts, there was 17-18! (Maybe due to the extension cord being stranded wire instead of solid???)

OK - progress. The problem must be something weird with the romex feeding power to the fixture, somewhere between the light fixture and the breaker box. Certainly NOT what I wanted to find out with a ceiling I have to destroy to see above, but at least I know where the problem is and can work toward resolution. To confirm this, I disconnected the incoming power wires and connected the extension cord as the source of incoming power. After confirming everything was wired right, I plugged in the extension cord into an outlet on circuit #12 & tested. Unfortunately, the low voltage power is still there.


I'm officially stumped. The low voltage being higher with the extension cord connected to the switch is probably a clue of some sort, but I'm not smart enough to know what it means.
 
 

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