Reading 120 volts from COM to ground

[Dave XXXXX]

Thank you for reading my (first) post.

I turned a space heater on and the entire circuit went dead but the breaker did not trip.
After turning the breaker off and on the outlet shows no voltage from Com to hot side.
But both com and hot show 120 volts to the ground.
And with the breaker turned off, a continuity test from COM to HOT shows a reading of .045 ohms
At the same time there is no continuity from ground to either wire.
Checking at the breaker end shows 120V to the com rail in the ON position.
And no continuity to com in the off position.
Also the boxes are plastic (or fiberglass) and it appears the non insulated ground wire goes to the
com rail in the breaker box, but I haven't traced it yet to verify.

I think I may have a small short from com to hot somewhere, but I really don't know for sure.
Any help would be appreciated.

Thanks, Dave303

 

[jeffmattero76]

First, I don't know what you mean by "COM". Is there a 3 way switch that you are trying to turn on to make the space heater work?

To test, start at the breaker and put one probe on the breaker screw, and the other probe on the neutral/ground bus bar. You should have 120 volts there. If you don't, you likely have a bad breaker. Be sure that you have turned the breaker to the fully off position before turning it back on.

Post back what you find.

If you are calling the white wire the "COM", that is incorrect. The white wire is called the neutral.

Thank you for reading my (first) post.

I turned a space heater on and the entire circuit went dead but the breaker did not trip.
After turning the breaker off and on the outlet shows no voltage from Com to hot side.
But both com and hot show 120 volts to the ground.
And with the breaker turned off, a continuity test from COM to HOT shows a reading of .045 ohms
At the same time there is no continuity from ground to either wire.
Checking at the breaker end shows 120V to the com rail in the ON position.
And no continuity to com in the off position.
Also the boxes are plastic (or fiberglass) and it appears the non insulated ground wire goes to the
com rail in the breaker box, but I haven't traced it yet to verify.

I think I may have a small short from com to hot somewhere, but I really don't know for sure.
Any help would be appreciated.

Thanks, Dave303

 

[joecaption]

I'd also be shutting the breaker off and removing the outlet from the wall to see it was backstabbed instead of wrapped around the screws.
Space heaters draw a lot of power, and backstabbed connections can cause an overheat or short because of the poor contact.
Still no joy, start looking for a tripped GFI.

 

[Blue Jay]

Sounds like you have an open neutral, other things plugged into the curcit are what is causing your readings to ground.

 

[JoeD]

If by com you mean neutral, then the reading you have is indicating you have an open neutral.
Start looking for a loose connection. If the entire circuit is dead that loose connection could be in the panel.