Electrician here. Measure voltage at the outlet. It should be +/- 10% of nominal voltage. Eg. 207-253 in 230 volt land. You have to measure under load, so plug

Electrician here. Measure voltage at the outlet. It should be +/- 10% of nominal voltage. Eg. 207-253 in 230 volt land. You have to measure under load, so plug in some high current device. If voltage drops below 207 while a resistive heater is running, call somebody.