Weird reading on electric 4 way circuit???

[Mark42]

Just hooked up a 4 way light circuit in the basement. I don't have any recessed cans hooked up to the circuit, just a wire hanging from the ceiling. So I attach a neon test lamp with wire nuts to the feed and test the switches. Everything seems to be good, all the switches turn the neon bulb on and off in all the combinations of on/off. But I notice as I walk past the neon light that when it should be off it is actually glowing very dim. I put my tester across the leads with the neon bulb connected and it reads 17 volts across the black and white wires. Also 17 volts from black to ground and zero from white to ground. I flip a swithch and the bulb glows bright and shows 121 volts from black to ground. I flip the switch again and its back to reading 17 volts. Then I disconnect the neon bulb and test across the black and white and the tester shows zero volts. Same for black to ground and white to ground. Flip the switch and the volts read 121.<br /><br />So I am confused. I get a 17 volt reading on a circuit that should be open, but only if there is a neon bulb attached to it. Without the bulb, the voltage is zero.<br /><br />What is going on here?

 

[m1rodrig]

Re: Weird reading on electric 4 way circuit???

Does it do the same thing with a normal bulb? Is it possible the neon bulb may take a while to discharge, maybe it is storing some kind of current? That is kind of weird.

 

[Paul Moir]

Re: Weird reading on electric 4 way circuit???

Sounds just like a tiny leak to me. A neon bulb will glow with very little current going through it.<br /><br />Is your meter digital? If so the leak can be on the order of 30 megohms. Just a little moisture in one of the switches will do that. It's possible that all your wiring is inductively picking up current from a nearby wire, but your wire would have to run parallel and close to a wire carring fairly large currents for that to add up to anything.

 

[Mark42]

Re: Weird reading on electric 4 way circuit???

I don't think a regular bulb will glow on just 17 volts. I was wondering if wires running in parallel could cause induced voltage. I usually don't use the neon tester, so I don't know if this is common or not. <br /><br />Sure seems weird to me.

 

[Paul Moir]

Re: Weird reading on electric 4 way circuit???

No, the 17v will drop to 0 when you put a regular bulb on it. If your meter was digital, it presumably had an input impedance ('Resistance') of 10 megohms. You can look it up in the manual. So what I'm saying is that pulled the 120v down to 17v just by connecting the meter. That would indicate that the 120v was 'shorted' to your line by a resistance of 60 megaohms (sorry, I miscalculated last time).<br />There's plenty of assumptions there, but you see what I'm getting at?

 

[Mark42]

Re: Weird reading on electric 4 way circuit???

Paul,<br /><br />Yes, my meter is digital. I don't quite follow the science here. Why would voltage register after the circuit is opened with the neon bulb but register no voltage with the tester only?

 

[Paul Moir]

Re: Weird reading on electric 4 way circuit???

Ooohhh, oops - sorry about that Mark.<br /><br />Hmm, thats definitely strange. It gives me an idea but I think I better think it over more before I go shooting my mouth off again. Did both 'posts' in the neon bulb illuminate or just one?

 

[Mark42]

Re: Weird reading on electric 4 way circuit???

I can't tell for sure but it looked like both posts. It is a small little bulb. One odd thing is that I can find a spot in the 4 way switch and a 3 way switch that makes the bulb go out completely. Sort if that middle spot in the throw. <br /><br />If I didn't use a neon bulb I never would have noticed this. It's not enough to even feel it with my fingers. And tonight I got a full 120v through my hand twice. Thats why I don't like having two circuits in one mult gang box. Even if one circuit is off, the other is still on and all those live screw connections on switches are just waiting for you to bump into them. Ouch!

 

[CalicoKid]

Re: Weird reading on electric 4 way circuit???

Mark, do you have a dimmer installed as one of the threeways? Is your meter autoranging and showing you milivolts when the switch is off and not volts?

 

[TwoBallScrewBall]

Re: Weird reading on electric 4 way circuit???

My guess is that a cpapcitor or something in the neon light is storing a small amount of electricity that your meter is picking up.

 

[Paul Moir]

Re: Weird reading on electric 4 way circuit???

If there was DC leaking into it somehow, the neon bulb may be acting like it would in a relaxation oscillator with the capacitance in the wires, converting DC to AC. So without it there ought to be a (high) DC voltage on the line, but with it in it'll be an AC (really, pulsing rather than alternating) voltage.<br />But if that's what is going on, only one post on the neon bulb would light, and you would be able to read a DC voltage on the circuit when the bulb was out.<br /><br />It's a wild guess but it fits the evidence. It doesn't seem very likely to me though.

 

[heyttown]

Re: Weird reading on electric 4 way circuit???

Mt guess is a 3way dimmer switch.........They make all these switches to look the same now, and all it took was one person to look at a 3 way dimmer switch and put it back in the wrong bin...

 

[Mark42]

Re: Weird reading on electric 4 way circuit???

Nope, no dimmer, just two 3 way and one 4 way switch. Simple layout: 3-way, 4-way, 3-way. Line comes in and light feed goes out at the middle of the run in the 4-way box. This is simple multi-switch circuitry using a pair of travelers and hot/neutral. Not re-inventing anything here.

 

[K Hultgre]

Re: Weird reading on electric 4 way circuit???

Paul,<br />How about the wiring acting as an antenna and the neon bulb is reacting to the RF ?<br /><br />Mark,<br />do you have wireless internet, WIFI, or live close to a relay tower ?

 

[chuckz]

Re: Weird reading on electric 4 way circuit???

STOP!!!! It's called leakage current. Assume the series resistor for the neon is 100k ohms. Using ohms law the current required to produced 17 volts is 0.17 milliamps. The source impedance that is producing the leakage current is 120volts minus 17 volts divided by 0.17 milliamps = 605k ohms. Initially, that looks low but if I understand the set up right,there are three switches in parallel. If each switch is leaking equally,each has a leakage current of 0.17 milliamps divided by 3 or 0.06 ma. This means each has a resistance of 120 volts divided by 0.06ma or 4 Million ohms. Wipe all the fingerprints off the switches and clean them with alcohol, with the power off, and the neon may go out when the power is turned back on. There is no problem with the circuit. <br /><br />When the voltmeter is inserted in the circuit without the neon, the meter has an input impedance of at least 10 million ohms. That is an increase by a factor of 100. The voltage will drop by a factor of 100 to 0.17 volts.<br /><br />It's either this or aliens with ray guns screwing with you

 

[Paul Moir]

Re: Weird reading on electric 4 way circuit???

That's what I thought too, but it goes away when he disconnects the test bulb??<br />Had not thought about RF. I don't think WIFI or other low power sources could ever do, but if Mark is next door to WPIG pumping out 100,000 watts of easy listening...

 

[chuckz]

Re: Weird reading on electric 4 way circuit???

Yes, because the series impedance increases to the meter's input impedance. This reduces the current flow and therefore reduces the measured voltage drop.

 

[Paul Moir]

Re: Weird reading on electric 4 way circuit???

I get you now. Makes sense to me. <br />I was thinking upside-down...

 

[chuckz]

Re: Weird reading on electric 4 way circuit???

The problem with the RF theory is I don't think his hand held DVM has the bandwidth to measure voltage at RF frequencies.<br /><br />Mark,<br /><br />Bottom line, you don't have a problem, what you're seeing is normal.

 

[Paul Moir]

Re: Weird reading on electric 4 way circuit???

Nor a diode or diodish thing (ever notice this property of mercury tilt switches?) to rectify it to make a relaxation oscillator work..