How can I determine whether a bad neutral is on my side or utility side?

Question

I'm experiencing the classic symptoms of a bad or lost neutral and want to determine if the issue is my responsibility or the utility's. Voltage fluctuates plus or minus 6 volts when a large 120V load is placed on either leg of my service panel. I noticed that my lights would briefly dim when the boiler of my 1500w espresso machine cycles on, then they would briefly flicker when it cycled off. The dimming and flicker is consistent for any high-draw loads (vacuum, toaster, microwave).

I can also hear a feint crackling sound right behind my service entrance neutral when one of these loads is on. I presume this is arcing, but I can't see where it originates. I put a clamp-on ammeter around the main neutral and the ground conductor (connected to water entrance, transitions to PEX after). The majority of the current is on the ground conductor.

I noticed that the electricians that wired my home (built in 2017) didn't use the knockouts on the main panel, but rather drilled their own holes to put nm clamps through. There were a fair amount of metal shavings all around the neutral conductor.

The connections to the main lugs appear to be very tight. I systematically turned off each breaker while monitoring the current on the ground conductor and there was always current on it in parity with the load on whichever breaker(s) were still on. Are there any other steps I can take to determine where the problem lies? I'm in the US.

UPDATE
The utility company came out and initially thought everything was fine. I explained that I pretty much eliminated any neutral issue from the service panel main breaker on down. I insisted that he check the connections in my side of the meter and he found that both the neutral and ground were ‘very loose’ so he tightened them a few turns. I put a clamp on the ground wire in my panel and now I’m reading between 0.5 and 2 amps. Worse than zero, but better than the 40 I saw yesterday. The main neutral is now carrying most of the difference between the two legs. No more flickering or dimming lights under any loads and my voltages are pretty much even, only fluctuating between 121 and 124 volts, regardless of loads. I’m going to have to call them again tomorrow to remove the seal on the meter base to give me access to the terminals so I can fully tighten them.

Also, sorry about the unclear picture. It is looking straight down at the main neutral lug. Some debris is visible. The alt text poorly explained some of that.

Answer 1

You have successfully identified a Lost Neutral scenario, and checked everything that is possible for you to check.

The only remaining places it can be are inside the meter pan, or at one end or the other of the overhead service drop.

The next step is to walk the overhead service drop and look for any bad connections with the service wires. Look for places where it is hanging from the 2 insulated conductors instead of the bare neutral.

Other than that you can call the power company and ask permission to open up the meter pan to inspect inside it, but that's not the usual cause. I suppose you could throw on a bunch of heat loads onto one phase and go out to the meter pan and listen for arcing, but that's grasping at straws.

Really, you've at the point at which I would just call the power company and report an outage.

Answer 2

This happened to me recently and I can offer some important tips.

1. Call the power company.
2. Don't take "no" for an answer.
3. Tell the customer service folks an electrician found a problem with the transformer neutral and he needs a lineman to inspect it for him.
4. Call the power company again if you don't get a visit from a lineman on an emergency basis. By that I mean, within a day or two max.
5. Expect a lineman to bring a SuperBeast or similar tools for testing your meter base and other connections.
6. A lineman can't repair anything on your side of the service entrance, but should be able to eliminate all utility connection issues.
7. If the problem is in your panelboard, you really need to get an electrician out there ASAP.
8. In the meantime, if anything goes wrong with your grounding system, or if you have any ungrounded appliances such as a 3-prong dryer or a poorly connected furnace, there will be a severe fire hazard.