48volts on opposite leg of mwc

[bobbyho]

I got a call from a customer saying their dishwasher ckt tripped. When I went out, I found a 12/3 run 51 feet to a box at the side of the kitchen sink. Black wire was doing outlets, red wire was doing dishwasher. There are no other points between panel and the switch/outlet box. I isolated the red wire from the dishwasher circuit and still at the panel I measure 48 volts on the red wire. I shut off the circuit for the black and the voltage goes away on the red. There is no sign of a short between the red and black or the red and neutral. Can this be an induced voltage over such a short distance or is there something that I am completely forgetting about? Thanks in advance for any ideas.

 

[peter d]

Can this be an induced voltage over such a short distance or is there something that I am completely forgetting about? Thanks in advance for any ideas.

Yes, this is most definitely ghost voltage. Use a Wiggy style tester instead of a DMM and it will go away.

 

[iwire]

Use a Wiggy style tester instead of a DMM and it will go away.

Or use both at the same time and watch it go away. :smile:

 

[e57]

Or use both at the same time and watch it go away. :smile:

Classic.... :grin:

 

[electricalperson]

ive heard of this and people called it coupled capacitance. i see this kind of problem with spare wires inside of boxes ran from panels. this is why i use my k60 knopp tester and not a dmm. the new fluke t+ pro is a nice voltage tester too

 

[Absolutetruthz]

I got a call from a customer saying their dishwasher ckt tripped. When I went out, I found a 12/3 run 51 feet to a box at the side of the kitchen sink. Black wire was doing outlets, red wire was doing dishwasher. There are no other points between panel and the switch/outlet box. I isolated the red wire from the dishwasher circuit and still at the panel I measure 48 volts on the red wire. I shut off the circuit for the black and the voltage goes away on the red. There is no sign of a short between the red and black or the red and neutral. Can this be an induced voltage over such a short distance or is there something that I am completely forgetting about? Thanks in advance for any ideas.

So what caused the circuit to trip?

 

[bobbyho]

Well, I eliminated the second leg of the multiwire circuit and gave it a dedicated feed to the dishwasher. The dishwasher then hit a particular stage in the heating cycle and tripped again. It then became the appliance guys troubleshooting. I still don't know why the 48volts was on the second leg of the mwc but it is no longer a mwc. I think it was coincedence that had me looking at the 48volt "cross" as the culprit. I have learned to check for backfeeds on mwc just from experience in the past but this time it wasn't the problem.

 

[George Stolz]

...the new fluke t+ pro is a nice voltage tester too

I was looking at the specs last night, and it looked to me like it was still sensitive to induced voltage, like a DMM. Is it?

 

[SmithBuilt]

George I had the same question so I emailed Fluke here's the thread where I posted the answer.

http://forums.mikeholt.com/showthread.php?t=96023


I'm considering trying one.

 

[quogueelectric]

Does open neutral ring a bell for anyone??

 

[electricalperson]

I was looking at the specs last night, and it looked to me like it was still sensitive to induced voltage, like a DMM. Is it?

well i dont think its like a DMM. it operates like a solenoid tester but it has a screen that displays volts. It doesnt say milivolts or a decmil point after the volts. It picks up anything over 10 volts on to work. I use it just like a knopp tester and thats all i think of it as. It does have a built in flashlight, gfci tester, ohm meter and continuity tester but in no way will it replace a DMM. Iguess they market it as a safer alternative to using a wiggy since the current draw of the tester itself is not as high as a wiggy so it doesnt blow up or melt at higher voltages. Anyone ever have a wiggy blow up?

 

[LarryFine]

Iguess they market it as a safer alternative to using a wiggy since the current draw of the tester itself is not as high as a wiggy so it doesnt blow up or melt at higher voltages. Anyone ever have a wiggy blow up?

There's no reason it should, within its voltage limits. It does not present a short circuit.

 

[electricalperson]

Does open neutral ring a bell for anyone??

did the OP have 120 volts between red and neutral? if he lifted both connections and had 48volts between the red and ground or neutral then its probably ghost voltage. pretty weird but i had this situation with a 3 wire cable too. a wiggy is a much better choice for everyday testing. only time i would break out the DMM for this is when i see the voltage onthe wiggy is not quite at 120 and it doesnt have the normal vibration feeling.

 

[LarryFine]

Does open neutral ring a bell for anyone??

Well, if it does, there are some very serious wiring problems going on. :wink:

 

[ramsy]

I was looking at the specs last night, and it looked to me like it was still sensitive to induced voltage, like a DMM. Is it?

Last week, while buzzing, lighting up, and showing 120v display voltage on energized wires, my T+ pro did not register anything on another wire, which did caused my tic tracer to chirp. My tic tracer specs voltage sensitiviy from 50 - 600 volts.

The T+ pro specs higher impedance than solenoid testers (wiggy's). That higher impedance may permit its CAT IV 600 vac rating, for transient protection. I doubt wiggy's have a CAT rating for transients, much less CAT II or III.

 

[iaov]

well i dont think its like a DMM. it operates like a solenoid tester but it has a screen that displays volts. It doesnt say milivolts or a decmil point after the volts. It picks up anything over 10 volts on to work. I use it just like a knopp tester and thats all i think of it as. It does have a built in flashlight, gfci tester, ohm meter and continuity tester but in no way will it replace a DMM. Iguess they market it as a safer alternative to using a wiggy since the current draw of the tester itself is not as high as a wiggy so it doesnt blow up or melt at higher voltages. Anyone ever have a wiggy blow up?

I've heard of them blowing up but have never seen it. We used them in a mill to test 480 all the time for years and never had a problem.

 

[bobbyho]

When I first got to the customers house the breaker was tripped and unable to reset. I took the red wire off the breaker and checked it with a tick tracer, simply out of habit. It lit up the tick tracer. I then got out the VolCon and it lit up 2 out of the 3 led lights on it. I then went and got a digital meter and saw 48 volts. One more meter, this time an analog and it confirmed the 48 volt cross. There was not an open neutral in the box where the circuit went to and split. The best way of describing this is in telephone terms as a "cross". If you had 2 phone lines crossing you would see voltage on on line while the other is disconnected from the source. In telephone, this could be caused by a number of different things. In electrical you would expect real exciting things to happen. Usually a breaker tripping but not in this situation. Hmm, ever notice how easy it is to explain something when you're able to draw it out on a piece of cardboard and "talk" about it. I have to become a more articulate writer but thanks all for bearing with me for leaving out such obviously important details.

 

[electricalperson]

I've heard of them blowing up but have never seen it. We used them in a mill to test 480 all the time for years and never had a problem.

im sure the insulation can fail if you leave it on voltage longer than its rated for. If that happens im sure it could technically "explode". but i never seen it happen or had it happen to me thank god.