49V of Stray Voltage on a disconnected switch?

[dsereni]

I've come across this situation (49V across the neutral and Hot when switch is off. Single Phase 120/240V) in multiple residences while changing out fixtures. Are there any tricks for locating and rectifying this problem?

 

[PetrosA]

Yes, a low impedance multimeter. See Fluke, Agilent et al. for options.

 

[dsereni]

A Duh moment

A Duh moment

I appreciate thecomment about the Multimeter, but.........that's pretty obvious. Not all of usare seasoned electricians (yet) and need some help on the basics. i.e. Whatcould be the possible causes of the stray voltagebe, and how can one troubleshoot the culprit and correct it. Short of going through every connection inthe house, and maybe that is the solution.

The reason it'sconfusing is... with the switch off, the ungrounded conductor is isolated, but still (using MULTITESTER)across the neutral and the ungrounded conductor, we read 49V? I believe thevoltage is travelling back along the neutral but since the ISO conductor isisolated:

1. why do I still read voltage

1. What king of situation is causing the stray voltage

1. How can one troubleshoot and Locate the situation causing the problem?

Thanks for your timeand help, this is a great site where electricians at all levels can benefit.

 

[don_resqcapt19]

There is no problem to trouble shoot. This is normal when using a high impedence tester. The voltage is transfered to the conductor by capacitive coupling or induction.

 

[PetrosA]

Like Don said, you don't have a problem - unless a low impedance tester shows the same voltage (it probably won't). This isn't STRAY voltage, but PHANTOM voltage introduced in a floating (unconnected) wire by capacitive coupling. Capacitive coupling is how tic testers work. Your body mass is capacitive coupled with ground, so voltage in a wire will complete the "circuit" and the tester will light up. That doesn't mean there's any real voltage moving through you, just the signs of that voltage. A high impedance multimeter (~10 megaohms) is sensitive to this induced voltage and will give you a reading of the capacitive coupling but in reality you have no useful voltage available. You will see this phantom voltage at almost all three way switches and some switch loops, especially with burned out lamps or non incandescent lights where your switch return doesn't have a solid connection to neutral through the lamp.

 

[kwired]

Like Don said, you don't have a problem - unless a low impedance tester shows the same voltage (it probably won't). This isn't STRAY voltage, but PHANTOM voltage introduced in a floating (unconnected) wire by capacitive coupling. Capacitive coupling is how tic testers work. Your body mass is capacitive coupled with ground, so voltage in a wire will complete the "circuit" and the tester will light up. That doesn't mean there's any real voltage moving through you, just the signs of that voltage. A high impedance multimeter (~10 megaohms) is sensitive to this induced voltage and will give you a reading of the capacitive coupling but in reality you have no useful voltage available. You will see this phantom voltage at almost all three way switches and some switch loops, especially with burned out lamps or non incandescent lights where your switch return doesn't have a solid connection to neutral through the lamp.

I would like to add the voltage is real, it just does not have a strong enough source to sustain the voltage when a load is placed across it. The reason the low impedance meter shows no voltage is it places enough load across this voltage that it shorts it out and it is not a strong enough source to sustain any voltage. Same voltage will return when the meter leads are removed. Touch it with your fingers and you are low enough impedance to short it out, and you don't feel it because it is not a strong enough source to have any impact on you.

 

[K8MHZ]

Re: Tic tracers

Re: Tic tracers

Capacitive coupling is how tic testers work. Your body mass is capacitive coupled with ground, so voltage in a wire will complete the "circuit" and the tester will light up.

I don't need to be anywhere near my tic tracer for it to work. I use it as a breaker finder. It will beep when stuck into a live receptacle no matter if I am touching it or not.

I often wonder where the myth that a tic tracer relied on a person's body to work properly came from.

 

[K8MHZ]

There is no problem to trouble shoot. This is normal when using a high impedence tester. The voltage is transfered to the conductor by capacitive coupling or induction.

If verified by a solenoid tester or equivalent, that is correct. There still exists a possibility of a real problem, one a DVOM isn't really suited for verifying.

It boils down to how to use test equipment. A DVOM is a poor troubleshooting tool. It's a great measurement tool, but for troubleshooting, a solenoid tester or even a test light would be a better weapon of choice.

OP should take the next 35 bucks he sees and get a Vol-Con XL. It is a reasonably priced solenoid tester that works well and indicates the nature of the voltage with lights. A voltage from coupling or induction will only light up one or two of the lights, but won't indicate on the voltmeter. A Vol-Con can pay for itself on a single job just by reducing man hours.

 

[don_resqcapt19]

...I often wonder where the myth that a tic tracer relied on a person's body to work properly came from.

Probably from application notes like this.

 

[macmikeman]

This thread is the premier reason to carry a knopp wiggie and learn its limitations and how to properly use it. I got mine on for every job. I have other styles for use as well, such as the fluke digital one, but the knopp wiggy is the way to fly if you do much troubleshooting.

 

[K8MHZ]

Probably from application notes like this.

Interesting. Either they are just plain wrong, or the tester I have is not a cap coupled tester.

I don't have to be anywhere near mine. I just checked. It must be a fluke. Oh, no. It's a Greenlee GT-11. Fluke is the company that the app notes came from.

I can tape mine to a piece of PVC and use it to check overhead feeds.

Thanks for the link. Maybe a Fluke tester needs a person on one end, but not my particular Greenlees. Which, BTW, are the best I have ever had and I have tried several brands. An EC has one of the Flukes and I don't care for it compared to a GT-11.

Different technology, maybe?

 

[K8MHZ]

This thread is the premier reason to carry a knopp wiggie and learn its limitations and how to properly use it. I got mine on for every job. I have other styles for use as well, such as the fluke digital one, but the knopp wiggy is the way to fly if you do much troubleshooting.

Just curious. What do you feel the advantage of the Knopp tester is over the Ideal Vol-Cons? Especially the VolCon XL?

Oh, and Fluke has been making meters in China and importing them here for years. Take a ride to Sears and check out the Flukes they sell there. Look close for country of origin.

 

[don_resqcapt19]

Interesting. Either they are just plain wrong, or the tester I have is not a cap coupled tester. ...

I think they are all capacitance and they may work without a person, but the application note is CYA on the part of the manufacturer. I did not read through the set of notes that I linked to, but there is one set out that says they may not work if you are standing on a fiberglass ladder.

 

[Dennis Alwon]

Is there a dimmer in the circuit? I have seen dimmers bled thru to the light when the switch was off.

 

[K8MHZ]

Is there a dimmer in the circuit? I have seen dimmers bled thru to the light when the switch was off.

Especially if they aren't all the way off. Some people just turn them down until there is no light, and don't actually turn them off.

 

[PetrosA]

I don't need to be anywhere near my tic tracer for it to work. I use it as a breaker finder. It will beep when stuck into a live receptacle no matter if I am touching it or not.

I often wonder where the myth that a tic tracer relied on a person's body to work properly came from.

My Fluke works that way too. There are situations when it hasn't worked unless I was actually touching it, or has beeped for phantom voltage in which case I hold it by the back end with two fingers to minimize the signal (sort of a manual sensitivity adjustment ). Some tic tracers are way too sensitive though and will beep on any EMF in the area.

 

[ptonsparky]

I really don't like the Fluke non contact tester. Sorry Fluke. I like the ones a local CED store has with the local logo on it.

 

[hurk27]

Is there a dimmer in the circuit? I have seen dimmers bled thru to the light when the switch was off.

Actually dimmer, fan controls, and any switch with a pilot light will do this.

As to the OP, try putting a load on the two point you are taking a reading from, if the voltage is still there it is real, if it goes away it is a phantom voltage, putting a 1k ohm resistor across your voltage meter leads will also rule out phantom voltage.


Any wire that is not connected at either end but is run along with energized conductors will pick up a phantom voltage via capacitive coupling from the energized conductors, and high impedance meter such as most DVM's that have a 10 meg per volt input will read this voltage as they do not place a load on the voltage, by putting a 1k ohm resistor or other load across your meter leads, this voltage will disappear, solenoid type meters such as "wiggy's" or "Ideal Volt-Cons" place a load on the circuit being measured and will only report the real voltage, many digital meters are now being made with this feature using a selectable switch to place this load on the circuit being measured.

 

[macmikeman]

Just curious. What do you feel the advantage of the Knopp tester is over the Ideal Vol-Cons? Especially the VolCon XL?

Oh, and Fluke has been making meters in China and importing them here for years. Take a ride to Sears and check out the Flukes they sell there. Look close for country of origin.

Stick the two side by side and notice how simple it is to unhook the knopp leads from the body of the unit, and also the more compact size. However, knopp's have a down side. They don't take to falls too well, even short ones. How is the Ideal when it comes to taking a fall?


I used to own an Ideal solonoid tester. I didn't care for it. Too fat. But I did like the continuity tester part of it . Nowadays I pack a knopp and a fluke 65 (?) in my tote sack onto the jobs. The Fluke has that amprobe slot to boot, and thats a nice touch. Fluke for controls, and knopp for resi work or general lighting circuits.

 

[K8MHZ]

Stick the two side by side and notice how simple it is to unhook the knopp leads from the body of the unit, and also the more compact size. However, knopp's have a down side. They don't take to falls too well, even short ones. How is the Ideal when it comes to taking a fall?


I used to own an Ideal solonoid tester. I didn't care for it. Too fat. But I did like the continuity tester part of it . Nowadays I pack a knopp and a fluke 65 (?) in my tote sack onto the jobs. The Fluke has that amprobe slot to boot, and thats a nice touch. Fluke for controls, and knopp for resi work or general lighting circuits.

Thanks.

The Ideal gets knocked around a lot, but I haven't dropped it off a ladder yet. I don't like the leads that came with the Ideal, so they got modified with a utility knife. The Ideal has, for lack of a better term, shock resistant plastic. It's not glass hard like the plastic used in the last Knopp I saw. Perhaps Knopp needs to use less brittle plastic.