I've got a vexing issue in an old house, 1928, that I just bought. I get dimming that is not necessarily related to motor surges. The house has a 200 amp service, but some old and new wiring. I had an electrician out who said the dimming was normal in a house of this age.. but I can't see why with the service that it should be "normal". There doesn't seem to be any abnormal loads on any give circuit. I just measure the volts in most outlets and in each the meter went from 114/115, both at the beginning and end of a circuit, basically throughout the house. I measured an outlet right next to the box, and got the same reading. I read on here that 5% drop is maximum, and it appears that's where I start... I live in a major suburb near a major system, Dominion, I find it hard to believe they wouldn't know it if they were delivering too little juice. Any ideas on what else I can check... I've already had the electrician look at the grounds and neutrals in the box, and he tightened everything down. He said the wire all looked good, old Bx and Romex, but good shape. Thanks in advance.

Measuring voltage like you did is basically a futile exercise.

1st: a couple of questions
1. Does all of the house dim or part of the house dim?
2. When does it typically happen? Any large loads running like the AC?

Only partially one or two lights at a time, not on a specific circuit. Motor load will do it, but not necessarily on lights on its circuit. They dim and come right back up. There is one light in dining room, which on the same circuit as the frig, but only the frig and one other outlet, so I assume it's when the compressor kicks on, that makes sense. But lights do it intermittently by themselves, but not all lights at once.

But it'll do it without ac, washer, or disposal. What's also interesting, don't see it when garage door opens, that has a motor. I've got s sub panel, that was the house's original fuse box, and it's hooked into one circuit on the box, could that have anything to do with it?

OK, what you need to do is:

1. Determine if it's sub panel circuits or 1/2 of them like below.

2. Determine if it's confined to one or the other leg of the 240.
This would probably mean: is it circuits on every other breaker in the fuse box. Counting 240 breakers as taking up 2 spaces.

Do you have underground or overhead wires?

What I am suspecting, is a whole group of lights dim and that there are lights in the house that won't dim. If it's the sub panel circuits then it's an interior problem. If it's one leg of the 240, it could be in the overhead connection to the house, if you have one.

Meaning, it could be your problem or the utilities problem. If there is a light that never dims? That is a good sign. Find a light(s) in the sub that never dims and the main that never dims.

You can check the sub-panel and see if the neutral and ground busses are isolated. If you don't know how to do that, post a picture using go advanced.

If you can say that all circuits on L1 dim and none on L2 dim and an electrician came out to the house and checked the connections inside, then it's time to call the utility to check their side of the system.

What is the lowest voltage scale on your voltmeter for AC?

Most of this is over my head, but I'll check if it's only isolated sets of lights and see if they are the fuse circuitry... I've been wondering if it's something on the line outside which dangles from a line that runs down the street in front and then ts to my house, and has a fairly long run. All the outlets I tested all read the same thing 114/115, none higher none lower. The setting I put it on was 200, which the guy in the store told me to try. Is it possible that if Dominion took me up to 117 to 120 volts the problem would go away? The electrician didn't seem to think so and although he tightened down the connections in the box, he didn't do anything to the fuse box.

As I said, measuring the voltages mean NOTHING. A poor unloaded connection will read the supply voltage. Only heavily loaded circuits matter. Measuring the voltages o ground at the AC breaker while it's running might tell us something.

Measuring voltages at the main while the AC is on might help too.

AC = Air conditioner