Hot to ground = 87 volts

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mphillipps

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I was asked to check if a bedrooms receptacles had proper grounded. My 3 pronged plug in tester showed 2 amber lights indicating the receptacle was wired correctly. I then did a fallow up test checking voltage across hot and neutral. It read ~120 volts. Next, I read across hot and ground. It read 87 volts.
I've not seen this before. How can it be explained?
 
Bad or no real ground. Try reading the voltage with some sort of load on it, like a Wiggy:

314QPHSZDCL._SL500_AA300_.jpg
 
My guess is that it is not really grounded, the grounding conductor is open and all you are reading is phantom voltage.
 
mphillipps said:
I got the 87v using a Fluke. What would a Wiggy tell me that my Fluke would not?
Click to expand...

It would put a enough load on the circuit to eliminate any phantom voltage readings. It would be even better if you used both your fluke and wiggy at the same time.

If the 87 volts stayed rock solid I would look for a poor connection, if the 87 volts fell to zero I would look for an open connection.


Please see link Phantom Voltages - NEMA
 
DP520

DP520

I agree with WIMaster I think you may have a ground issue. I had a problem like this once. I could check voltage from hot conductor to nutral and would have 120v; from nutral to ground 82v; from hot to ground 240v. conclusion the 240 volt a/c conpressor heater had shorted out and the a/c unit was not truly grounded because the home was a sub panel and there was only 3 conductors a,b,n. This ended up feeding b phase back to ground thus creating 240v from hot conductor(A) at duplex to ground at duplex. Hope this helps this is my first post.
 
kbsparky said:
Bad or no real ground. Try reading the voltage with some sort of load on it, like a Wiggy:

314QPHSZDCL._SL500_AA300_.jpg
Click to expand...
Am I correct then in assuming that this wiggy is what the NEMA article refers to as "low impedance" test equipment? Makes a lot of sense that it would. I want one now, I guess I just always assumed they were a poor-man's analog volt meter (Which there's nothing wrong with, if you're broke like me!):thumbsup:
 
Poor Mans Wiggy

Poor Mans Wiggy

Cowboyjoe said:
Am I correct then in assuming that this wiggy is what the NEMA article refers to as "low impedance" test equipment? Makes a lot of sense that it would. I want one now, I guess I just always assumed they were a poor-man's analog volt meter (Which there's nothing wrong with, if you're broke like me!):thumbsup:
Click to expand...

On 120V circuits you can use any wattage incandescent light bulb with pig tails as your tester. If the bulb lights (even dimly) it is real voltage (bad ground.) If it doesn't it is phantom (induced) voltage and will go to zero (no ground.)
The typical Fluke meter on V scale has 10 meggohms input impedance.
I measured around 3K ohms DC resistance on my Knopp wiggy and 12 ohms on a 75W bulb, so there is the difference.

TT
 
Here in the UK it is common practice to use a test lamp to test for real voltage.
The use of a regular household bulb and bulbholder is discouraged, and is prohibited by most employers.
Special test lamps are sold for the purpose, these consist of a 240 volt 15 watt miniature lamp in an enclosed holder, connected to a pair of test leads.
The wire is double insulated, each test prod contains a fuse, and a series resistance is also in one test prod.

http://http://www.pat-services.co.uk/martindale-mtl7-drummond-test-lamp-1800.htm?utm_source=froogle&utm_medium=ppc&utm_term=1800&utm_campaign=froogle

Link shows the product in widespread use by UK electricians.

The lamp lights brightly on 400/415 volts, and less brightly on 230/240.
"wiggy" testers are virtually unknown here.
 
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Some digital meters have a 'low Z' setting which puts enough load on the tested circuit to eliminate 'phantom voltage'. They draw enough current to trip GFCI's which can be handy for checking the GFCI.
 
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