85V on neutral after space heater on circuit...?

[rrschw]

I'm not at all a certified electrician, but I have a strong self taught background in electricity and electronics.

We moved into a new home this year, and Austin got cold this week. I put a space heater in my room for the first time, and after an hour or so it flipped the breaker. Or so I thought.

The breaker was still in its on position.

Looking more into it today with the volt meter I'm realizing that there's 85V across ground and neutral, which kind of explains why electronics are not working, but the lights that are on this circuit still are.

I'm utterly confused how I'd end up with 85V on the neutral lead of this circuit, especially without flipping a breaker.

Any ideas what might be happening here?

 

[Lucien Nunes]

There is probably a bad connection in the neutral, that was only slightly high in resistance to begin with. But when presented with the higher current load of the space heater, overheated and has now gone very high in resistance. Now when even moderate load is applied to the circuit the neutral voltage rises to meet the hot. The actual voltage you measure will depend on the load, and so will the fire risk caused by the bad connection. Trace it back outlet by outlet / switch by switch towards the panel. Hopefully it will turn out to be in an accessible fitting, maybe a bad backstab connection or a loose wirenut. Don't forget it could be in the last outlet that is showing normal voltages, rather than the first one with abnormal voltages.

 

[rrschw]

There is probably a bad connection in the neutral, that was only slightly high in resistance to begin with. But when presented with the higher current load of the space heater, overheated and has now gone very high in resistance. Now when even moderate load is applied to the circuit the neutral voltage rises to meet the hot. The actual voltage you measure will depend on the load, and so will the fire risk caused by the bad connection. Trace it back outlet by outlet / switch by switch towards the panel. Hopefully it will turn out to be in an accessible fitting, maybe a bad backstab connection or a loose wirenut. Don't forget it could be in the last outlet that is showing normal voltages, rather than the first one with abnormal voltages.

As far as I know there was no load on the circuit when I was measuring it…?

Thanks for the pointer in isolating it. I’ll go through and see if I can pin down a resistance in the line.