Neutral voltage

mavrck

Member
Location
ky
I went on a service call today and had to figure out why a breaker was tripping . While trying to figure out the issue I noticed if I had the grounds in th j box apart and I went from neutral to ground I get 30 volts and the hot to ground be 80 volts

But if I had all my grounds in the j box tied together I would get proper voltage hot to ground 120v and 0v neutral to ground.

I understand why I received 80 volts hot to ground , I would contribute that to a bad ground. But why would I get voltage on the neutral? Thx
 

mavrck

Member
Location
ky
Digital fluke meter
Ground was #10 back to ground bar at panel, everything was pvc conduit and box

The path back to neutral bar is #8 wire.

everything is underground and existing so limited knowledge other than what is In the panel. I had trouble locating all the wires exact path because I couldn’t find the raceway back into the building
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
What happens to a light downstream of this point? Does it dim? If so, there's likely a break in the neutral pathway that is dependent on the EGC.
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
To keep it simple, assume there are two equipment ground wires: #1 that comes from the bond at the panel, and #2 that goes over to an outlet box, for example. The voltages from hot to neutral, and also hot to ground #1 would remain unchanged after you took the two ground wires apart. However, ground wire #2 is now disconnected and it's therefore susceptible to picking up "stray" or "phantom" voltage from its capacitance to the hot wire. And so ground wire #2 could now have a fraction of the hot-to-neutral voltage, in this case 30V/120V = 0.25 or 25%.

So when you measure the 30V between the neutral and ground don't think of it as a voltage on the neutral, because the neutral hasn't changed. It's the ground wire #2 that has changed and it now has a voltage of 30V relative to both the neutral and to ground #1.

These comments are based on my understanding of what you were doing in post #1. Perhaps you could provide more detail of where the ground wires were going to, and the rest of the circuit if appropriate.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Another example of why I use a solenoid tester for everything, unless I need to know the exact voltage, which still requires a load for accuracy.
 

mavrck

Member
Location
ky
Basically from what I could tell this circuit come from the panel and then tied I. To three separate j box feeding equipment.
Unfortunately all piping is under black top and the feed from building was ran under plywood in a attic
 

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
I’m curious is a solenoid tester the same as a dummy tester?
If not what is the advantage
Dummy tester or idiot stick, ticker, non contact tester is like this:
1617789310870.png
Seleniod tester is like this:
1617789995734.png
Different than your digital multimeter in that it utilizes circuits power to operate original models did this via a seleniod no battery needed. Some newer models uses circuitry to replace the seleniod.
Dummy stick will show even trace induced voltages or phantom voltage thus one reason not totally reliable for presence of voltage testing.
 

Dsg319

Senior Member
Location
West Virginia
Occupation
Journeyman Electrician
I went on a service call today and had to figure out why a breaker was tripping . While trying to figure out the issue I noticed if I had the grounds in th j box apart and I went from neutral to ground I get 30 volts and the hot to ground be 80 volts

But if I had all my grounds in the j box tied together I would get proper voltage hot to ground 120v and 0v neutral to ground.

I understand why I received 80 volts hot to ground , I would contribute that to a bad ground. But why would I get voltage on the neutral? Thx
Continuity between neutral and EGC? Resistance between the two?
What was the load?

Amp clamp around the EGC under load and measurements
Also what kinda of OCPD?
 
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Flicker Index

Senior Member
Location
Pac NW
Occupation
Lights
You'd get similar peculiarity on the floating conductor on a 3-way switch. Either the red or black is always floating. They're never connected to live at the same time. This is due to capacitive coupling as others have mentioned.

Intermittent trips are always tricky. It's probably a nail through a cable, crappy sheath stripping nicking the wire or a stranded whisker brushing up against bare ground somewhere. Check in the box where dimmers are if present since they often use stranded wires.
 
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Dsg319

Senior Member
Location
West Virginia
Occupation
Journeyman Electrician
What happens to a light downstream of this point? Does it dim? If so, there's likely a break in the neutral pathway that is dependent on the EGC.
I would say the same thing. The way I think of it is with egc unspliced. He doesn’t get 120volts phase to neutral. Being something else is in series with neutral between him and the panel. Likely the earth via the neutral being broken. And than when he splices egc’s back together there’s a low impedance path back to the source.?
 

kwired

Electron manager
Location
NE Nebraska
Dummy tester or idiot stick, ticker, non contact tester is like this:
View attachment 2556095
Seleniod tester is like this:
View attachment 2556096
Different than your digital multimeter in that it utilizes circuits power to operate original models did this via a seleniod no battery needed. Some newer models uses circuitry to replace the seleniod.
Dummy stick will show even trace induced voltages or phantom voltage thus one reason not totally reliable for presence of voltage testing.
Capacitive coupling is what they depend on to operate, capacitive coupling is what causes "phantom voltage"
 
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