jea48 said:
Are you sure you have an Equipment Grounding Conductor at the outlet?
dpop response:
100% most definitely; on both outlets being discussed. I can take my multimeter and read 121.6 volts across the hot and neutral (no load), and the exact same voltage is measured across hot and the EGC.
You will get the same measurements on a bootleg ground.
L to EGC on a bootleg ground is actually from L to neutral.
N to EGC is actually From N to itself. Naturally it will measure 0.00V
What is a Bootleg Ground and Why is it Dangerous?
dpop said:
My microwave oven consumes 14.6 amps during operation (measured using the amprobe meter). Volts available at the outlet with the microwave off was between 121.3 - 121.5. Volts available at the outlet with the microwave on was 117.9. N-E volts 00 with the microwave on or off.
"N-E volts 00 with the microwave on or off. "
Sure sounds like a bootleg ground to me. (Assuming you were making a good solid connection to the N and EGC with your DMM test probes.)
I completely understand VD on hot and neutral. Thanks, but no further explanation is needed on that. My curiosity was always with the N to EGC.
I don’t think you do fully understand L to N VD in a current carrying circuit.
IF you have a VD on a loaded circuit. Actually measured it, (which you did (L to N), then you will, should, have measured the Voltage Drop across the length of the neutral conductor, when you measured for voltage from N to EGC. Can’t have one without the other.
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Food for thought:
As for the voltage measured from N to EGC. IF the EGC is a solid low resistance/impedance connection with a high level of conductivity then it is assumed to be a good, so called earth ground. Therein at the same zero ground potential as the electrical service main Grounded Conductor, The neutral conductor. (They are Bonded together at the main panel.)
Therefore the way I look at any voltage measured from N to EGC, which is the result of a measured VD across a connected load from the Hot to neutral of a branch circuit, imo, should be considered as an above ground voltage... There’s one to ponder... Any EEs in the house?
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I remember reading in the NEC (National Electrical Code) years ago there is/was a maximum allowed resistance measured from the neutral conductor to the EGC conductor at the end of a branch circuit. Just going from memory it was not more than 2 ohms or 1 ohm. I’m thinking 1 ohm.
Test:
Branch circuit de-energized. Verify circuit is dead.
For a good test:
Make sure there is not any loads connected to the circuit. Unplug everything from outlets. Check for ceiling lights that may be on the circuit. Make sure light switches are off. Measure for resistance.
I measured for resistance at the two 20 amp dedicated branch circuits in my 2ch audio room. Both measured 000.3 ohms each. (Fluke 87 DMM.)
The two branch circuit are 10/2 NM cable (Romex) 75 ft each from panel to wall outlets.
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Hot-neutral is the load voltage. Voltage should read about 120 V (typically 115 V to 125 V). You measure exactly 118.5 V.
- Neutral ground is a voltage drop (also called IR drop) caused by load current flowing through the impedance of the white wire. Let’s say you measure 1.5 V.
- Hot ground can be thought of as the source of voltage available at the receptacle. You read 120.0 V. You note that hot-ground is higher than hot-neutral. In fact, hot-ground is equal to the sum of the hot-neutral and neutral-ground voltages.
Diagnosing Power Problems at the Receptacle - Fluke Corporation