How to Hook a Voltmeter to a Lamp

A voltmeter reading outside a particular range may indicate problems with a lamp.

A voltmeter is a device used to measure circuit voltage. A voltmeter must be wired in parallel with the circuit to obtain the voltage across two points in a circuit. If you are trying to check the voltage of a lamp, it is necessary to connect the voltmeter across the electrical leads of the lamp bulb receptacle. This allows the voltmeter to take a measurement of the lamp voltage while the lamp is turned on.

Instructions

1. Turn the lamp switch to the “Off” position. Remove the lightbulb from the lamp socket.

2. Turn on the voltmeter and set the measurement scale to “Volts AC.”

3. Connect the red voltmeter probe to the center metal ring inside the lamp socket. Connect the black voltmeter probe to the threaded metal sleeve inside the lamp socket. Check the voltage reading. The voltage reading across the lamp terminals should be between 110 and 120 volts AC.

Tips & Warnings

• If the voltage is less than 105 volts or more than 125 volts across the lamp terminals, turn off and unplug the lamp. This aberrant voltage reading may indicate a problem with the lamp or the electric circuit.

References

• Bucknell University: Measuring Voltage
• Don Vandervort’s Home Tips: How to Repair a Broken Light Fixture
• Second Chance Garage: How to Read and Interpret a Voltmeter