Use an AC voltmeter to measure the hot-to-neutral voltages at representative receptacles in an area or in the branch circuit panel board. The hot-to-neutral voltage should normally be within the 115 to 125 V range. It should not fall below 100 V with heavy loads on the circuit or rise above 130 V during no-load conditions. A significant difference in line voltages to receptacles taken under typical load conditions indicates overloaded circuits or faulty wiring and requires further investigation. An optional means of testing for adequate wiring is to measure the line voltage with and without a load connected to the other half of the duplex receptacle being tested. Make sure that this load, when combined with other loads on the branch circuit, will not exceed the rating of the branch circuit breaker