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One phase-neutral voltage reads hi under load and the other phase-neutral voltage reads low under load, AND both phases are equal under no load. Definitely sounds like a bad neutral connection. I'll bet that leg to leg voltage doesn't change much from loaded to no load. I would check the neutral splice at the weather head.

Mike
I had PC change neatral connection at weatherhead, had them back to check trans and connections, the only thing not checked is outside meter. I will have them check that too.
But now I think the problem is inside because voltage with no load at the line side of main breaker is steady as I mentioned in previous posts and when the branch circuit breakers are turned on the voltage changes. My problem is trying to isolate the trouble because it does not seem to be on one particular circuit. I shut off all circuits with motors, all 2 pole breakers that share a neatral and it still dimmes.
Mike

Sounds like you have a main going bad. Just had one were the voltage was good on the line and good on 1 leg. The other leg of the load side voltage was jumping up and down depending on the load. went from 90 to 120v. They lost a couple of power supplies on some computers that didn t have bat backup. Did water leak onto the main? What manufacturer is the main?


Ob
Sorry missed that u changed the main. I would be checking the meter neutrals and considering the lower seu cable may be failing as mentioned.

SO...what brand of loadcenter is it?

Hi
It is a Murrey panel which has a main breaker that I replaced. It is fairly new and it has 2 neutral blocks on each side connected by a flat pan cake type buss that connects to each neutral block. The service is wired with copper Se cable which looks just fine. The bonding screw is installed and connected to the neutral buss and the ground wires are also connected. The dimming will occur when any significant load is applied any where in the house. Very strange, still scratching my head.
Mike

The voltage fluctuation that you measured does not sound like enough to dim lights .
Still there should be none .
Really need to know where voltage is dropping .
If it drops at SE cable , above main then problem is before that .
Other possible causes are : loose bolts in panel , burnt bussbar , loose neutrals , loose or bad main.
It is just guessing without knowing how far back the voltage drop goes