Power drop when Microwave/dehumidifier turns on

Question

Recently I have been beginning to notice that whenever my microwave (800 watts) turns on, my lights dim quickly and voltage drops down from 124v to 120.2 volts. (I tested it on a different circuit from where the microwave was plugged in. However when the dehumidifier turns on the lights flicker even more, and voltage drops from 124 to 118 (on startup) and 121 on compressor on. Is this normal or am I loosing a neutral? I got my panel looked at earlier this year and everything looked good, but the service drop and the connections in the meter have not been replaced/inspected for more than 15 years. With gas dryer, microwave, and dehumidifier on it’s at about 116

Answer 1

Some connection on the affected circuit is not good and has a high resistance. Your wording suggests that this is new behavior, so it's presumably some change happening to the affected connection. Could be you have damaged feeder cable to the house. 15 (or 40) years should not be a factor of itself (50+ years is far from uncommon for trouble free electrical service installs), but if you have symptoms, something warrants investigation.

If you are checking voltage on a different circuit, that suggests that the bad connection is on the feeder supplying both circuits.

If the bad connection is on a neutral, heavy 120V loads would cause some other circuits to go higher voltage while others went lower. If all other circuits go to lower voltages, that suggests one of the hot lines as the culprit; but if you have only checked one or two other circuits, you may simply not have seen the ones that go up, yet.