Weird Electrical Situation

I ran into a weird electrical situation this morning. I got a call from someone who wanted a thermal scan of their electric panel. I went over there, and he told me and showed me how the lights throughout the house dim when almost anything in the house is turned on - even small loads like the garbage disposal.

He read online that this could be caused by a loose neutral, and that a thermal camera might be able to find it. I saw nothing unusual with my camera. Since I was already there, I did a little investigating. I plugged in my Suretest circuit analyzer to measure voltage and to see what happens with the voltage when various loads were turned on.
Here’s what happened.
With nothing on, the voltage was about 117
Turn the dryer on - voltage went as high as 135
Turn on deep fryer or garbage disposal - voltage up to 140 - 145
Turn on microwave (with dryer running) - Voltage dropped from 135 to about 120

The Suretest was plugged into a receptacle on the same phase as the deep fryer and the disposal, but opposite the microwave.

Obviously, its not my job to solve this for him, and I suggested that he call an electrician, but the engineer in me wants to figure out what is going on.

Any ideas??

I made a video of what the Suretest was showing during all this, but don’t see how to post a video.

Loose neutral lug, unbalanced loads. Places to check: panel, meter, service drop, pole. Best left to an electrician or local utility. If it’s intermittent it can be hard to find. Just went through a similar scenario with an open (intermittent) lug at the pole. Half the house would go dead when a tree branch pushed the lug just right.

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regardless of whether i can isolate a “thermal exception”
i advise clients with similar issues to hire a competent electrician & pass on collecting fees unless i was hired by the electrician

These types of voltage readings are almost always caused by an open neutral. This is a very dangerous situation that should be corrected immediately.


In my home the kitchen lights dim when the disposal is turned on then brighten up when turned off. A local electrician told me it was caused by a shared neutral home run. What are your thoughts on this and could it be what is causing the OP’s issue?

Something often overlooked is a corroded exterior service disconnect often along the ocean.

It could be your issue due to voltage drop but the OP stated that his voltage actually was higher than 120 volts (up to 145 volts) which would not occur from a normally functioning shared neutral of a MWBC (multi-wire branch circuit).

The OP also mentioned the lights dimming, that was what made me think of my own place and why I asked. Electrical isn’t my strong suit and was curious. If the voltage increases or spikes and the lights dim, then would it be safe to assume there’s more than one problem?

When there is a problem with the system neutral the normal 120 volts on a branch circuit can change. It may fluctuate 30 volts or more in either direction up or down. Applying say 150 volts to something only rated for 120 volts can cause serious issues especially to sensitive electronics. So if lights see a voltage drop of 30 volts they will severely dim, a 30 volt spike and they will get very bright.

Not necessarily. When the neutral is open 240v appears across the “on” circuits in the home. Two of these circuits will be in series, half attached to one 120v leg and half attached to the other leg. A series circuit will show a voltage ‘drop’ across each load. The exact voltage drop (from 240v) will depend on what circuits on each half of the system are “on.” As a result of different loads on each half of the system (remember there’s no neutral) the voltage drop (voltage used by) across each device could be higher than 120 or lower as Robert said above.


I understand the light bulb scenario, didn’t know there could be that much of a swing in voltage though without throwing a breaker. Seems to me it would be magic smoke time with a surge like that. Thanks for the info.

Breakers trip from overcurrent, not voltage.


Bob gave a more detailed reason why this happens. As he stated basically you end up with a 240 volt series circuit with different loads connected in series. The current in a series circuit is the same but the voltage changes across each load which is the voltage drop across the load that Bob mentioned.

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The homeowner texted me the following info this evening.

They just left a few minutes ago, but it turns out (electric company) was servicing my house and a few others incorrectly. They actually were running almost no electricity to our homes when compared to others.(my neighbor was included in this as well apparently) In consequence he was saying our houses were pulling power from wherever they could. He said this is the reason it was showing such a high voltage at different times. But yes, it was their service that caused this all along.
Not only that but he discovered that our lugs on the outside box were melted together because the neutral was in fact not grounded on their service box. The neutral was actually almost entirely loose, causing all the dimming and everything within my home.