Testing the Wattage of a Unit

Before testing the wattage, Bryan pulls the disconnect. When you pull a panel, it’s best to shut the power off to prevent parts from coming off and shocking you.

The Testo 770-3 is a multimeter, so it can read several different electrical values, including amps, ohms, and volts. The Testo 770-3 can also measure wattage directly, so you don’t have to take two separate voltage and amperage measurements and multiply them to find the wattage or power. To measure power with the Testo 770-3, you would turn the dial all the way to the top (W). You will have to use the amp clamp and the meter leads to take the amperage and voltage simultaneously.

Bryan uses the amp clamp to measure one of the main wires coming into the unit. He then puts alligator probes on his meter leads and checks the voltage at two different contacts. At this point, the power factor is at one, or it’s a unity power factor. The closer the power factor is to one, the better; a value below 0.9 may indicate that the power is out of phase.

After putting the disconnect back in, we determine that the total wattage is 4.572 kilowatts, which is consistent with our amperage reading of 20.7 and voltage reading of 213. However, you need to be careful to isolate the clamp; otherwise, it may try to read the amperage of other nearby wires and give you inaccurate measurements.

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