High voltage present when switch off

[mallen9595]

Hi. I'm replacing two ceiling lights in a 1950's era home. Both switches are individually looped such that each controls one light. I have taped the white line to block to show that the switched line from each switch is actually hot. However, here's the problem: Even when off, I'm reading 27-30v on each of the switched lines! This seems too high for a phantom voltage, even though I am using digital meters. What could be causing this?

FWIW, the room is fed by a main that reads a consistent 120v. As far as I know, there is nothing else on this main (though a resistance/continuity check, when off, shows darned close to 0 ohms!) and seems to be the most normal part of the whole circuit. When the switches are on, I get a good 120v on each switched line.

[kactuskid]

I have taped the white line to block to show that the switched line from each switch is actually hot.

I don't understand what you're saying here, makes no sense to me. I'm thinking you connected the two together to prove it's a switch loop but not sure. So, I'll try to explain a few things and maybe I'll answer your question by doing so.

If these switches have both a black and a white wire connected to them then they are wired in a switch loop fashion, meaing that the power comes into the circuit from the light. This means the white wire is actually a hot wire and not a neutral wire, so this white wire should be remarked at both ends to indicate it is a hot wire. Do this by coloring it black using a majic marker.

So, if you turn this switch off it will not disconnect the power in the circuit going to the light, the only way to remove the power is to open the breaker for this circuit. And this should be done no matter what you're working on.

If you've opened the breaker and you still read 30 volts then yes, rest assured that this is phantom voltage. These voltages can even be higher than 30 volts. Use an analog meter to verify and I bet you won't read anything. Here's a link that'll help explain some of the details.
http://repairfaq.ece.drexel.edu/REPA...ml#APPFAQJ_019

Hope this helps and ask back with anything else.

[mallen9595]

Thanks for the reply and for the advice. I'm familiar with this configuration, and I do shut off the power except to test voltages. When the breaker is open, there is no voltage anywhere. But when it's closed, there is 119V on the supply line to the light box. Connected to the supply hot is the black lead to the wall switch loop, with the white lead (colored black, since it's hot) as the return leg. When the wall switch is closed, there is 119V across the return leg (from the switch) and the neutral, which is as it should be. But when the switch is off, there is 27-30V.

I also get some really odd voltages which I didn't mention before. Originally, just to keep things simple, I mentioned just what was happening at each lightbox, with nothing else connected. But there are actually three lights in this installation, each with a separate switch loop, and feeds from the main supply going between them. I've tried disconnecting all the switches and I get 119V on the feed at all three light fixtures. Everything's ok so far. And when I connect one of the three wall switches in a switch loop configuration (remember, each switch powers one light and nothing else), I get the aforementioned voltages. Everything is still okay except the possibly phantom 30V when the switch is open. Now, here's the problem: When I start connecting in the other switches, I get voltage drops across the main. I don't remember if the switches have to be open or closed, but I get 90V with two switch loops connected, and 60V with all three connected. I have even tried replacing the switches themselves, but this still happens. I get 119V at outlets in this house regardless, although they are on another circuit. FWIW, I am using two different meters, so I can't blame the meter.

The 30V "phantom" on each open switch when it's open is very steady. Next week is the next opportunity I will have to check this circuit, and I will try an analog meter as you suggested and also look at the FAQ. But I can't explain the apparently voltage drop by having two or more switches tied into the circuit. I've never seen this before. That's why I think there's more than phantom voltage at work here. Also, this house has abnormally high energy bills, and I wonder if there's some kind of leak contributing to this mess. Although the wiring in this house is all grounded, it is 50 years old.

[HayZee518]

analog meters are best testing out circuit voltages. even a neon test light would be ok. digitals are just too picky when reading raw electrical values. The most extreme use I got from a digital is measuring the ground resistance of a semi-conductor paint on a motor winding in a 16 foot rotor in a hydro plant. We measured somewhere in the range of 199 megohms on the gradient paint from one end to the other.

[suprheat]

Make sure that you don't have any cheap panel surge suppressors hooked up. They use a MOV that connects across the 220v at the panel and can actually back feed the whole bus. Or as in my house I use X-10 devices. I needed to install an MOV to make certain circuits work with X10. I have to make sure I turn off the breaker with the MOV whenever I work on other circuits as it backfeeds. Another problem you might have is a poor ground system in your panel and it's "looking" for another path to go.
Good Luck