Unusual home AC voltages at light switch

[LA1]

I have a flood light outside of the house that was added some 50 years ago. It does not work. I took both incandescent flood lamps out, both are bad. the one the whole inside is completely black inside the other has a rattle. Tried a new lamp did not work. I went to the switch and disconnected the black and white wires. black is the hot wire ...right? between the black and white is 25 ac volts aprox. between black and ground 3v ac and white and ground 25v ac aprox. I am sure that the electrician , a neighbor, connected up to an existing run somewhere. No breakers tripped, as far as i know all circuits in the house are working. What do u think happened?

 

[wyliesdiesels]

Bad connection

 

[bbbarracuda]

Those sound like induced voltages just picking up from nearby wires.
It could have been disconnected sometime in the past.

 

[65ranchero]

Bad breaker?
anything else on the circuit?

 

[sparky 1971]

Is it a switch loop, meaning the black and white are both on the switch with no other cables feeding the switch? Or are there two cables in the box with the white wires tied together and two black wires on the switch?

 

[ybnormal]

like @bbbarracuda , I think it may be induced voltage though I do think 25v is kind of high for that, but then I'm nowhere close to being an electrician.
installed a new dishwasher 7 yrs: chkd the voltage (120v), found the breaker and flipped it off, chk voltage again because I'm paranoid and now it has 7v....WTF?
I very carefully wire-nutted the connection and installed. flip the breaker back on and measure and we're back to 120v

 

[engineer2]

Could that circuit in question have a shared neutral (MWBC)? If something is powered on the other hot, you'll see N-G voltage.

 

[Bert_]

Is it a switch loop, meaning the black and white are both on the switch with no other cables feeding the switch? Or are there two cables in the box with the white wires tied together and two black wires on the switch?

That was my first thought too, switch loop.

Just because a wire is white doesn't mean it's a neutral!

 

[65ranchero]

Just because a wire is white doesn't mean it's a neutral!

If so shouldn't that be taped black?

 

[alfredeneuman]

If so shouldn't that be taped black?

The rule for marking white wires came with the adoption of the 1999 NEC.
Before that there was no rule.

 

[Forgottonia]

Is it a switch loop, meaning the black and white are both on the switch with no other cables feeding the switch? Or are there two cables in the box with the white wires tied together and two black wires on the switch?

^^This. I'll bet someone just ran the hot wire out to the switch and back. Not really the way you're supposed to do it--although I know there are switches like this in my house and building. /shameful guilty look on face

 

[sparky 1971]

^^This. I'll bet someone just ran the hot wire out to the switch and back. Not really the way you're supposed to do it--although I know there are switches like this in my house and building. /shameful guilty look on face

It can still be done, but with the fairly new requirements for a neutral in the switch box, it's 14/3 or sometimes a 12/3 that gets used for the loop. The neutral is just left sitting in the box waiting for a motion sensor with the black and red on the switch.

 

[sparky 1971]

If so shouldn't that be taped black?

Just because something is supposed to be done doesn't mean that it is.

 

[Jim greengo]

I have a flood light outside of the house that was added some 50 years ago. It does not work. I took both incandescent flood lamps out, both are bad. the one the whole inside is completely black inside the other has a rattle. Tried a new lamp did not work. I went to the switch and disconnected the black and white wires. black is the hot wire ...right? between the black and white is 25 ac volts aprox. between black and ground 3v ac and white and ground 25v ac aprox. I am sure that the electrician , a neighbor, connected up to an existing run somewhere. No breakers tripped, as far as i know all circuits in the house are working. What do u think happened?

Depends on how its wired,were the black and white both wired to the switch?

 

[Terry D]

If this is a switch leg, and it was wired correctly, the white should be the power coming into the switch and the black would be the return to the light. This way you would have a black and white to the light and not two whites. I would make sure that when you are checking voltages, is that you have a good ground. There could be 120 volts, but with a bad ground, you may only read 25 volts. Best thing is to read voltage at the light with the switch on.

Not saying this is your case, but I cant tell you how many flood lights I troubleshooted and found the center tab in the socket is bent to far in and doesnt make contact on the lamp. Make sure the power is off before you try this.