This is a weird situation. When my wife uses her hairdryer, the lights dim in the house. But…not always. It seems to only happen during the winter and only on certain days. At first I thought it was because there are 2 rooms that are heated electrically, which would only be on during the winter. I thought it was that the house had been wired wrong when these electrical baseboard heaters were installed. However, last time this happened, I went around to the rooms that are heated electrically, and turn off the thermostats. The problem still occurred.
The only other thing I can think of is that the problem seems to happen after we have a snow or rain storm. Could moisture be getting into the electrical connections to the house?? This may be coincidence…I can’t be sure. The problem does not happen at all during the spring, summer or fall. Only in the winter.