voltage to ground
- Thread starter laketime
- Start date
- Status
brian john
Senior Member
- Location
- Leesburg, VA
Could be an open ground.
What type of meter are you using?
Did you try measuring to a different ground, other outlets, other outlets in other rooms, water pipe, main service?
What type of meter are you using?
Did you try measuring to a different ground, other outlets, other outlets in other rooms, water pipe, main service?
alfiesauce
Senior Member
What kind of wiring is in the house?
N&T, MC, old non grounded NM, greenfield and rigid?
What do you have between neutral and ground at the devices compared to at the panel?
N&T, MC, old non grounded NM, greenfield and rigid?
What do you have between neutral and ground at the devices compared to at the panel?
MF Dagger
Senior Member
- Location
- Pig's Eye, MN
What kind of meter?
quogueelectric
Senior Member
- Location
- new york
Try ringing continuity from ground to neutral. Probably open ground.
ptonsparky
Tom
- Occupation
- EC - retired
Bifocals come into play for me on occasion. 40 mv vs 40 v.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
081209-1146 EST
laketime:
At the main breaker panel connect a long wire to the cabinet. This will be your reference lead to the meter. It is OK to use a high impedance meter, 10 megohm input, for these tests.
The main breaker panel should be directly connected to both the neutral and ground buses in the panel. These two buses should also be connected together in the panel.
Assume you have a metalic water pipe to the outside. Read the voltage difference from the panel to water pipe. With my Fluke 27 I read about 50 MV at home. You should not have a large voltage. If there is a ground rod read the voltage to it.
Next start probing different outlets for the voltage on the EGC and the neutral.
40 ft from my panel at my work bench I have 52 MV on the EGC and about 0.77 on the neutral with a load of some 8' Slimlines, a computer, and printer. With these off and the printer disconnected from a different computer that is powered from a different circuit I get 1.2 MV on the EGC and 2.3 MV on the neutral. If I connect the printer to said other computer, but with the shop bench still off, I get 30 MV to the EGC, and still the 2.3 MV on the neutral.
If you do not get a low voltage from the ground rod or water pipe look for problems between these and and the main panel.
Note: we can not assume that anything is correct. However, the main panel enclosure is still a useful reference point.
Suppose that it looks like the main panel enclosure is connected to either or both the ground rod or water pipe, then from this panel do you see a low voltage to various EGCs? Some close to the main panel and others where you have seen the abnormal readings.
Look at various neutrals with and without loads.
If you have a bad neutral from pole to main panel there won't be any great effect on the voltages from the main panel enclosure to the various EGCs and neutrals.
You describe hot to neutral as 120? Is this correct everywhere, and for both phases?
Then you describe hot to ground as 40 V some places but not others. By ground I assume you mean the third pin in the outlet, the EGC. At this same place check the neutral to the EGC. Is it 80 V? If not you probably have an open EGC. If you are dealing with an open EGC, then you want to place a 100 W incandescent lamp across your meter leads when you do the test from the hot line. This makes your voltmeter a low input impedance meter. If voltage drops to near zero, then you have a good indication of an open EGC.
.
laketime:
At the main breaker panel connect a long wire to the cabinet. This will be your reference lead to the meter. It is OK to use a high impedance meter, 10 megohm input, for these tests.
The main breaker panel should be directly connected to both the neutral and ground buses in the panel. These two buses should also be connected together in the panel.
Assume you have a metalic water pipe to the outside. Read the voltage difference from the panel to water pipe. With my Fluke 27 I read about 50 MV at home. You should not have a large voltage. If there is a ground rod read the voltage to it.
Next start probing different outlets for the voltage on the EGC and the neutral.
40 ft from my panel at my work bench I have 52 MV on the EGC and about 0.77 on the neutral with a load of some 8' Slimlines, a computer, and printer. With these off and the printer disconnected from a different computer that is powered from a different circuit I get 1.2 MV on the EGC and 2.3 MV on the neutral. If I connect the printer to said other computer, but with the shop bench still off, I get 30 MV to the EGC, and still the 2.3 MV on the neutral.
If you do not get a low voltage from the ground rod or water pipe look for problems between these and and the main panel.
Note: we can not assume that anything is correct. However, the main panel enclosure is still a useful reference point.
Suppose that it looks like the main panel enclosure is connected to either or both the ground rod or water pipe, then from this panel do you see a low voltage to various EGCs? Some close to the main panel and others where you have seen the abnormal readings.
Look at various neutrals with and without loads.
If you have a bad neutral from pole to main panel there won't be any great effect on the voltages from the main panel enclosure to the various EGCs and neutrals.
You describe hot to neutral as 120? Is this correct everywhere, and for both phases?
Then you describe hot to ground as 40 V some places but not others. By ground I assume you mean the third pin in the outlet, the EGC. At this same place check the neutral to the EGC. Is it 80 V? If not you probably have an open EGC. If you are dealing with an open EGC, then you want to place a 100 W incandescent lamp across your meter leads when you do the test from the hot line. This makes your voltmeter a low input impedance meter. If voltage drops to near zero, then you have a good indication of an open EGC.
.
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