How to Measure Single Phase Voltage

John DeMerceau

Single phase electricity is the technical term for electrical current that is generated by a single source of alternating (AC) current. Household electricity is single-phase as is electricity produced by a voltage inverter from your car, RV or boat battery. If you find that your electrical current malfunctions, or that your electrical equipment is not working well, you will want to make sure the voltage of your circuits is correct. While there are voltmeters, which are devices that measure only voltage, available on the market, most do-it-yourselfers use a multimeter on its proper AC voltage setting to measure single-phase electricity.

The electricity in your home is 120 volts single-phase AC current.

Step 1

Turn the dial on your voltmeter or multitester to the AC current setting that is closest to but higher than the rated voltage for the circuit you are testing. Choose a setting higher than 120 volts for household current, but note that some older air conditioners may run on 220 to 240 volt single-phase current. For instance, you can set the rating to 200 volts AC for testing a regular 120 volt circuit, and 1000 volts if there is no setting between 200 and 1000 for a 220 volt circuit.

Step 2

Insert a lead of your voltmeter or multimeter into each of the two top plug holes of any electrical outlet. Note the reading. Replace the outlet if it shows a reading of less than 120 volts for a regular outlet or less than 240 volts if it is for an older air conditioner. Repeat this step after installing the new outlet.

Step 3

Remove the protective panel from your electrical outlet if the reading you obtained for your electrical outlet is 120 volts AC (or 220 to 240 for an air conditioner outlet). Touch each lead to the exposed portion of wire at each screw terminal of your outlet. Perform this check with the wires to your room light switch if you are having problems with the lighting fixtures in your room. Note the reading. Run new wire as necessary or contact an electrician if your reading is less than the proper one.

Step 4

Locate the circuit breaker for the room or area where you are experiencing electrical problems if the reading for your outlet or switch wires is also the correct one for their rating. Find the wires that lead to the breaker and test them by touching one meter lead to each wire. You may have to remove your circuit breaker panel or remove the breaker from the panel to access the wires. Run new wiring or contact an electrician if your reading is low.

Step 5

Repeat Step 4 for the main circuit breaker if your reading for the room or area breaker wires is the correct one. Contact an electrician to run new wiring into your home if the reading is low unless you are completely familiar with the electrical codes in your area for wiring a home to your local grid.

Step 6

Use your multimeter according to the manufacturer's instructions to test amperage at all points mentioned in the steps above or call an electrician to perform other tests and find the source of your disturbances if the voltage tests properly at all points.