We own a house that we rent out that we had lived in for 20 years or so. It was built in the 1950s. The tenants recently said that the lights have been dimming for a few seconds at least once a day, perhaps more, usually in morning and afternoon, and all lights in house seem to be affected. Sometimes it seems related to dishwasher or furnace coming on, sometimes not. They've been tenants for two years and say it has been happening more in last couple of months, and they just informed me because I'm coming out to do annual maintenance (we live in another state).

My electrician said to call the power company first to check the pole and weatherhead; in his experience that fixed about a third of such cases--so I did.

The tech from the power company, who I talked with by phone, said that he tested the voltage on the two legs of the supply line using what he described as being essentially like "two meters and a hair dryer". At the main panel, he put the load on leg A, and voltage dropped on leg A and rose on leg B. He put the load on leg B and the voltage dropped on leg B and rose on leg A. He said it changed about 8-10 volts, which is much more than normal. He checked at the pole and weatherhead and voltage was good. Then he pulled the meter and tested behind the meter and found the same problem, which really surprised him, so he put the meter back in and tested the weatherhead again and it was good there. He concluded that there must be a neutral problem in the conduit that runs from the weatherhead to the meter and that we should get it fixed ASAP. He advised the tenant not to turn on any expensive appliances, or too many at once, or she might burn out some appliance from a rise in voltage (on the opposite leg, I assumed). He said the only time he's seen this problem is when someone tried to tap into the supply line before the meter to get free power, and he was apparently suspicious that was the case here--he asked how long we had owned the house, etc.

Since the problem is recent, last few months, and the tenants we have would almost certainly have not done something to the electrical system, I find it puzzling. I also think that if the problem were as he described, the tenants would see half the lights in the house brightening at the same time the others are dimming. My electrician hasn't yet visited the house to confirm this, but I wonder if the power company's service tech actually knows what he is talking about.

Does anyone have any experience with something like this?