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Earlier today, I read Acceptable ground to neutral voltage?, and thought it'd be fun to stick my multimeter in the socket and have a voltage to report back. Neutral to ground read 60 volts. My head went into a bit of alarm. Yet, I can't find the answer just yet.

My apartment is old... as in it has a coal door and electricity wasn't an original feature. The basement has very old circuit breaker boxes and almost all of the structural wiring down there is old school fabric insulated wire on ceramic knob and tube wiring. It seems likely that most outlets don't have a real ground. All of them are GFCI branches.

The following measurements are all digital multimeter outputs.

Bedroom

Hot <-> Neutral:     118 volts
Hot <-> Ground:      60 volts
Neutral <-> Ground:  60 volts
GFCI: trips internally, does not trip externally

Shorting neutral to ground with a 1 amp fuse did not cause the fuse to blow. Inserting a plug tester resulted in the middle light being solid and the two outer lights flickering. Hot to neutral measures 60hz. Other combinations vary wildly into the khz region.

Bathroom

Hot <-> Neutral:     118 volts
Hot <-> Ground:      80 volts
Neutral <-> Ground:  15 volts
Sink <-> Ground:     15 volts
Sink <-> Hot:        113 volts
Sink <-> Neutral:    0 volts
GFCI: trips internally, does not trip externally

Kitchen

Works properly. Measured resistance between ground and sink is 450k ohms. Hot carries proper voltage to neutral, ground, and sink. No voltage neutral to ground or sink, or ground to sink.

The question

Can anyone make sense of these readings?!

Further testing

Ground <-> disconnected 50ft length of extension cord:  24 volts
Ground <-> disconnected 50ft length of extension cord:  17-21 volts

Bedroom ground <-> kitchen ground:                      60 volts
Bedroom ground <-> water pipe:                          60 volts
Bedroom hot <-> water pipe:                             0 volts
Bedroom neutral <-> water pipe:                         113 volts

Bedroom hot <-> water pipe:                             2.8 mega ohms
Bedroom neutral <-> water pipe:                         lower and wildly varying
Bedroom ground <-> water pipe:                          OL / unmeasurable ohms

Sooooo... I currently guess that I probably have hot & neutral reversed through most of the house and ground is unbonded. I still can't figure out the 60 (15, 80) volt readings though unless it's capacitive (re: voltage read across disconnected wires). I suppose I'll get my hands on an analog meter to test with next.

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Is it possible to measure Ground <-> True ground where you are getting 60V neutral to ground? I suspect you don't have a true ground at the receptacle. –  Tester101 Dec 30 '11 at 17:17
    
I would suspect that the kitchen was rewired. –  Brad Gilbert Dec 31 '11 at 19:59
    
Depending on the meter, if there is a voltage on the lines it will give you false readings for your resistance. –  Kellenjb Jan 4 '12 at 1:41
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1 Answer 1

From all this, I conclude the following is likely:

  • Only the outlet in the kitchen next to the sink is properly wired.
  • All other outlets have hot and neutral reversed.
  • There is no ground connection.
  • Unexpected observed voltages (mostly 60 volts) are caused by stray capacitance.

I'll mark it accepted when I get complete confirmation.

Outlets need to have their hot and neutral corrected. Outlets need to be grounded or labelled as "GFCI protected" and "no equipment ground."

Fluctuating voltage from the actually hot line to true ground (the water pipe) is caused by current flow reducing the electrical resistance of the line. Voltage is otherwise high and stable for the capacitive currents as they don't induce enough flow.

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@ Jeff; Nice to see another Mainiac on here. Any relation to John Ferland? BTW, great answer. +vote –  shirlock homes Dec 30 '11 at 22:36
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I would suggest chasing the hots to a know earth ground to assure if neutral and hot are reversed before assuming that. Many show floating grounds, and open neutrals. I'm not convinced they all are reverse polarized until they are disconnected from the devices and tested to a solid earth ground. –  shirlock homes Dec 30 '11 at 22:42
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Then check the downline conductors with an ohm meter to see if any may have been junctioned and colors swapped. In other words, see the flow of conductors device to device, this will discover opens and crosses. It is a lot of work, take one branch at a time. –  shirlock homes Dec 30 '11 at 22:45
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