where is this mystery 35v coming from?

Jayne

Just here for the memes
Charter Member
Supporting Member
Multi-Factor Enabled
Joined
Dec 16, 2016
Messages
8,028
Location
Unincorporated Wake County
Rating - 100%
34   0   0
Removing ceiling fans from two rooms in an office and replacing them with LED ceiling lights. Easy.

Each room has two wall switches, one makes the fan go, the other the lights. The wiring is white/black to the fan, white/red to the light, common green.

Here is what I expected to get when testing:

switch #1 ON, you get 120v to white/red
switch #2 ON, you get 120v to white/black

However, what I found with the meter was:

switch #1 ON, you get 120v to white/red
switch #2 ON, you get 120v to white/black AND 35v to white/red
switch #1 and #2 ON, you get 120v to white/black and white/red
switch #1 and #2 OFF, you get zeros everywhere


So... where exactly is that rogue 35v coming from? Both rooms had the wiring the same and both had the 35v on the 'off' circuit when one was active and both the light and fan have been working for years AFAIK (wife is just moving into this office this week). Wiring looks original to the building (mid-90s) being covered in over-spray from the original white color the rooms were.

I can see some sort of mis-wire giving us 120v on both, but 35v? The fans were not physically hooked up when I was testing, just the multimeter so I'm not even sure what would be stepping down the 120v to 35v. Both rooms were exactly the same, and that 35v was rock steady in both.

I disabled switch #2 since it goes nowhere now and I didn't want 35v going to the new LED fixture if someone flipped that second switch. No idea what that would do to the light. But... for the last N years has it been that if someone had the fan running without the light the bulbs were getting 35v (yet not lighting up)?
 
Last edited:
Is there a dimmer anywhere in this setup?

Nope. Just two standard on/off switches.

The office is also empty so other than ceiling lights, the only thing plugged in anywhere is the cable modem / router box. Not even sure that's on the same circuit as the office lights.
 
Did you check the black and red wires back to ground? What you are probably seeing is a small phantom voltage from the switch that is turned on. There probably is no real voltage there.
 
touch the neutral to ground... does the GFCI Breaker trip in the panel ?
 
Did you check the black and red wires back to ground? What you are probably seeing is a small phantom voltage from the switch that is turned on. There probably is no real voltage there.

I did not. I was afraid to start poking around randomly at that point.

It's officially fixed like this, it's pretty clean for DIY. :)

upload_2020-1-13_15-31-45.png
 
I would have to see it.

1. Sounds like one of the wires is a traveler wire from another switch location.
2. “Green is common.” OP. Not sure what you mean but it’s the grounding wire to fans, lights, and possible metal box.
 
My guess would be that it's an induced voltage caused by mutual induction and / or parasitic capacitance from the non energized wire that is open circuited being run in parallel with the 120Vac energized wire.

Do you have a resistor you could put on the red wire to ground and then measure the voltage. If it is induced voltage, if you give it a discharge path the voltage should collapse.

I've ran into this on control wire run along with power wires. It can induce enough voltage and current to turn on an opto-isolator and make you think the circuit was active. Placing a load resistance across it fixed this.
 
Well, I finally replaced my faulty GFCI yesterday, so I'm pretty much an expert electrician at this point.

I'd say you have something wrong and it needs to be fixed. $150, please.
 
My guess would be that it's an induced voltage caused by mutual induction and / or parasitic capacitance from the non energized wire that is open circuited being run in parallel with the 120Vac energized wire.

Do you have a resistor you could put on the red wire to ground and then measure the voltage. If it is induced voltage, if you give it a discharge path the voltage should collapse.

I've ran into this on control wire run along with power wires. It can induce enough voltage and current to turn on an opto-isolator and make you think the circuit was active. Placing a load resistance across it fixed this.

I understood "red wire". :eek:
 
Kelly, are any of your switches the type that light up when they are off? If so the 35V may be part of the switch light.
 
Last edited:
Black & Red are hot, white is neutral (prob. what you mean by "common"?), green (or bare) is ground.

I would be really interested in seeing the wiring of the switches. That sounds like something is partially crossed, but it's weird that it's only in one direction.
 
My guess would be that it's an induced voltage caused by mutual induction
What I said but with more accurate terminology. Induced voltage was what I was looking for. I’ve seen almost the exact thing before. Wires run in the same path with wires with power can pick up induced voltage occasionally. I’m mechanical but work around plenty of electrical guys.
 
I had a blank cover in the living room for many years and this past year I put a fan/light combo in. I had 50 volts on a wire to the new fan/light combo when one of the switches was off. I had 5 switches total in two spots, 3 in one box, and two in another. The traveler wires were not correct and not marked. It took over 2 hours to determine the issue.
If you can’t use a meter to ohm out the wires you need an electrician on location. My situation also involved general lighting circuits commonly called receptacles fed from same circuit.
 
My guess would be that it's an induced voltage caused by mutual induction and / or parasitic capacitance from the non energized wire that is open circuited being run in parallel with the 120Vac energized wire.

Do you have a resistor you could put on the red wire to ground and then measure the voltage. If it is induced voltage, if you give it a discharge path the voltage should collapse.
.

This is likely what is happening. High impedance digital multimeters often show this sort of thin. Can you find an old analog meter? If it is just the induced voltage Noway2 describes, it should read zero on any analog meter without a power switch. (If it has a power switch, it may be an FET input meter that could have the same problem.)
 
This is likely what is happening. High impedance digital multimeters often show this sort of thin. Can you find an old analog meter? If it is just the induced voltage Noway2 describes, it should read zero on any analog meter without a power switch. (If it has a power switch, it may be an FET input meter that could have the same problem.)

I don't, but I've received another (off forum) confirmation that this is what I'm seeing. The tests are as everyone is describing, but since it's all back an 'in production' now I'm just going to leave it.
 
Thanks to all who replied, we can put this thread to bed now (unless more mockery of the switch plate and/or the fact that the switch color doesn't match the plate cover is required). I hate those 'ivory' colored switches and outlets but it's not my office so I won't have to look at that and the wife didn't notice.
 
28 posts in and this thread is worthless until somebody gets shocked with at least 220v
giphy.gif
 
Last edited:
28 posts in and this thread is worthless until somebody gets shocked with at least 220v
giphy.gif

If you get by 220 or more you get a Very bad copper mouth and you might even piss in your shorts. It is not fun.

the 35 volts may be from a loose ground wire in your electrical system.
 
Last edited:
If you get by 220 or more you get a Very bad copper mouth and you might even piss in your shorts. It is not fun.

the 35 volts may be from a loose ground wire in your electrical system.
Some old timers here know I’ve sharked myself with 220 not once, but twice.
Posted about it.
Good times.
 
575v is a beotch. Split my thumb open and arm hurt for 2 days afterwards.
 
My kids are out and paying their own electric bills. This is for my wife to not turn certain ones on that she never turns off!


14 and 17 at home with the same issue. At night every single light needs to be turned on to light their path to the kitchen, then left on.
 
@Jayne

I want to know where you acquired the toggle cover! Man, I could use a couple.

Had the wife pick them up at Ace Hardware on her way to the office. I just sent her a screen shot and they appeared 30 minutes later. Like amazon right-the-hell-now delivery.
 
Back
Top Bottom