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I’m having this issue with here I can't get a stable voltage reading coming out of any outlet in a particular room. I have a furman m-8dx power conditioner with a voltage meter that jumps anywhere from 120-138 at any given moment. Quite often, and unprovoked by any starting or stopping of major appliances. It rests for maybe 30 seconds around 127 or 128 and can jump in a matter of 2 seconds from 128 to 138 and back down to 120 and everything in between. This is happening often. It is more likely to fluctuate than stay stable at 127 which seems to be the average.

I called the power company out and they said nothing seems wrong and it could be a factory down the street which has to be miles around which sounds unlikely to me. I am suppose to operate on 120v but it’s always high and unstable. What can I do to test or fix this. The home was built in 2003

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  • Did you try the meter in other rooms? Commented Sep 28, 2023 at 14:45
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    There's a common failure of the utility wires which will cause 120V voltage to hop around madly. The two 120V legs add up to 240V, but the center is not being held to the center all that well. However, "major appliances" (240V) have no effect on this. Only 120V appliances affect it. Does your microwave pulse on and off during defrost mode? Stick a big mug of cold water in there and run 3 minutes of defrost, then go watch your voltmeter. If it hops up and down, you have a lost neutral. Commented Sep 28, 2023 at 22:07

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Get a decent multimeter. Make sure it us UL or ETL listed and rated as CAT II or CAT III for safety.

Test various receptacles around the house. If the numbers do not fluctuate when your power conditioner readings fluctuate then the problem is in your power conditioner. If the numbers do fluctuate then:

  • See if you have some high and some low. If some drop to 112 when others jump to 128 then you may have a lost neutral, which can be a breaker panel problem but is often a utility problem.
  • If they all only go in one direction, see if you have any 240V with neutral receptacles. Most common is an electric clothes dryer. If so, take readings there. You should have two hots and neutral (and ground, hopefully, but that is irrelevant to this right now). Check hot-hot and hot to each neutral. If hot-hot stays ~ 240 but one hot-neutral is up and the other down then likely lost neutral.

There are some other possibilities, but the starting point is to get readings all over the house. One circuit doesn't tell you much by itself.

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120V is a nominal target, and actual voltage can vary due to loads on it. Down under, it tends to be more stable and defined. But from other posts here, not so much is USA.

Some possibilities

  • Either your meter is not accurate or defective.
  • Or your meter is losing connection with the socket.
  • Voltage can vary if there are heavy loads that are being switched on or off, either on that circuit in your home or elsewhere on the street.

But none of this should affect anything in your home.

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