I need to test the wattage / amps of two light fixtures on a single circuit. I'm having issues with a smart dimmer and I'm trying to figure out if the amps / wattage exceeds the limits of the dimmer.

I have a southwire 100031s multimeter. Is it possible to test the wattage / amperage using this multimeter?


It sounds as if you want to measure wattage/amps of mains-powered lamps, which are probably powered from an AC source. Unfortunately the meter you mentioned cannot measure AC current; it does DC only.

Most (all?) lamps should be labeled as to their wattage. On the old incandescent bulbs it was printed right on the glass. Newer CFL and LED bulbs often have the wattage printed on the bulb base. If you can find the wattage marked on the lamps then you can add the wattages of all the lamps to figure the total load.

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If you can measure AC voltage, you can easily measure AC current as well. Just place a relatively low value resistor inline with the load, and measure the voltage between each leg of the resistor. Then divide that voltage by the resistance to get current. You can then multiply that by voltage again to get wattage.

For example, if you used a 1-ohm resistor and measured 0.5 volts across it, 0.5v/1=0.5A. Thus, 0.5A X 120v = 60W. Ohms law.

If you don't have a resistor handy, perhaps you can measure the resistance of an extension cord with your multi-meter and use that instead of an actual resistor. Remember to test the resistance of shorting the leads of the meter and subtract that from the measurement of the extension cord to get a more accurate resistance reading.

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