Line fault at the outlet -- do I need an electrician?

hilde45 OP269 posts

03-20-2020
7:26am

@bryhifi I have a digital multimeter. I use it to test car batteries. I suppose I might use that, too, no? In any case, I can get the three prong outlet if necessary.

The DMM will work just fine.

1) Set the meter to AC ~ auto volts or an AC ~ voltage scale above 150Vac.


2) Insert one test lead probe in the "U" shaped equipment ground contact hole of the wall outlet. Make sure you make good contact to the ground contact. Insert the other test lead probe into the Hot contact slot of the outlet. Make sure you make a good connection to the Hot contact. (The Hot contact is the smaller of the two slots.) You should read 120Vac nominal volts. *(If the reading is bouncing all over the place that is what is called a phantom reading, not a true reading.)
If you get a solid good 120V nominal reading that will tell you two things. The AC polarity is correct and a ground is present.

IF you do not measure 120 Volts nominal. That can mean Two things.. NO equipment ground, or Hot and Neutral reversed polarity.

3) Measure for voltage from the equipment ground contact to the neutral contact. The neutral contact is the larger of the two slotted holes on the outlet. Make sure the two DMM probes are making good contact. If you measure a good solid 120 nominal voltage then the Hot and Neutral branch circuit wires are reversed on the receptacle outlet. If you do not measure any voltage then you do not have an equipment ground.

Jim

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That's fantastic -- thank you so much. It's a snowy day in Denver today and I am shut inside. I'm printing this out for reference. 

heaudio123135 posts  

03-20-2020  
 8:58am  

"3) Measure for voltage from the equipment ground contact to the neutral contact. The neutral contact is the larger of the two slotted holes on the outlet. Make sure the two DMM probes are making good contact. If you measure a good solid 120 nominal voltage then the Hot and Neutral branch circuit wires are reversed on the receptacle outlet. If you do not measure any voltage then you do not have an equipment ground."

I think some clarification here for a novice. When you measure between ground and neutral at a receptacle, most multimeters will indicate some voltage, i.e 0.1 - 2.0V approx.

heaudio123

I think some clarification here for a novice. When you measure between ground and neutral at a receptacle, most multimeters will indicate some voltage, i.e 0.1 - 2.0V approx.

True, If #2 of my previous post above is met. Therein a properly wired receptacle outlet with a Correct AC polarity, and an equipment ground is present.

For the novice a difference of potential, voltage, measured between the neutral conductor and the equipment grounding conductor on branch wiring can be caused by, at least, two things.

1) VD, (Voltage Drop), on the neutral conductor due to the connected load on the branch circuit.

2) An induced voltage that is/may be created by the hot and neutral current carrying conductors onto the equipment grounding conductor.

Jim

Got it.