I have an electrical situation that has me puzzled. I was checking a friends garage outlets for polarity and I got a reading of 42volts from nuetral to ground. I traced the circuit back to a splice. Now the garages wiring was newer than that of the house. The garage is newer 12/2 with ground and the house(and the splice) is 12/2 without ground. What the heck is causing leakage from ground to neutral? My friend solved the situation by disconnecting the splice and ran 12/2 with ground back to the panel but I still want to know what was going on.
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suspect the nutral was backfeeding to groung..
What would cause a neutral to backfeed?
bad connections..
faulty device..
Thanks for your opinion. I suspect you are right. I've come across lots of electrical oddities that I suspect were committed by inexperienced DIY's. My favorite to date is the grounded 2 pole switch replacing a three way switch. Guess where one of the travelers was connected to?
Put a 15 watt incandescent light in parallel with your meter. That converts it from high impedance to low, and eliminates the floating line capacitance issue.
-- J.S.
I am gonna put my money on the floating ground. I had briefly considered that it could be leakage from a device on the circuit but realized when I was checking the outlet nothing was on or plugged in to any of the receptacles. Thanx for all the input, Now I can stop thinking about it.
With the garage ground not hooked up to anything, it's voltage level is "floating". In other words, it doesn't have a low impedance connection to ground, or to any other specific voltage level.
The voltage meter you were using has a very, very high input impedance; something over 1000 Megohms. When you connect it between the neutral, and the floating piece of wire running in the same romex with the neutral and the hot (that you thought was grounded, but wasn't), you form a circuit with the input to the voltmeter in series with the capacitance between the floating wire and the hot wire in the romex; this series combination is placed across the 120V voltage between the neutral and the hot. Even though this capacitance is on the order of picofarads (a millionth of a millionth of a Farad, the unit of capacitance), you still measure a significant voltage across it, since the impedance of the voltmeter is also very high.
You can put one lead of the voltmeter at ground, and the other on your finger, and if you're in an area with a strong electric field, you could see the same voltage level. it really doesn't mean anything, and is just the result of the voltmeter's ability to measure voltage sources with extremely high impedances.
Plain old floating ground. If the ground is disconnected it will tend to "float" somewhere between 0 and 120, usually near the middle.
Another possibility is that one of the devices plugged into a 3-wire receptacle in the garage had leakage current to it's case, that was then available on the ungrounded ground wire. This leakage current could exist whether the device was turned on or not.
This possibility seems more likely to me than the floating ground measured with a high impedance meter idea. It's easy to test though. Just unplug everything in the garage or turn off the breaker and see if the 42v goes away. If it is stray capactive pickup like Barry says, you will still read some tens of volts (because the breaker does NOT disconnect the neutral).
If on the other hand my theory is right, the voltage will drop to essentially zero with either maneuver. ( And if you SEQUENTIALLY unplug the garage devices, you will find out which device was producing the current. ) If I am right, it was a potentially dangerous situation, as someone elsewhere in the garage remote from the damaged device could have gotten a 42 v shock (say touching the wall plate screws on a switch while turning on the water spigot).
Since the problem has already been masked by replacing the wiring, you cannot actually carry out these tests (without going back to the panel and lifting the ground). Just to be safe though, I would suggest testing the leakage current on any devices that were connected to the garage power.
Rick
Generally if there is a leak to "ground" on an ungrounded circuit the "ground" will be at essentially 120V. OTOH, it's not at all unusual to see 40-50V on a "floating" wire, with enough current to light a neon tester and register on a high-impedence voltmeter (such as any cheap electronic meter).In any event, the "ground" isn't, and, unless everything's protected by a GFCI, is a major code violation.
> This possibility seems more likely to me than the floating ground
> measured with a high impedance meter idea. It's easy to test though.
> Just unplug everything in the garage or turn off the breaker and see
> if the 42v goes away. If it is stray capactive pickup like Barry
> says, you will still read some tens of volts (because the breaker does
> NOT disconnect the neutral). If you flip the breaker the "ground" will likely go to near zero, since there is then no 120V in the romex to capacitatively couple to the ground wire.