How to Wire a 240V Variac

Updated February 21, 2017

Variac transformers use an adjustable nob to vary its output voltage. A variac contains a single coil. The input voltage charges the coil. The adjustable output terminal slides up and down the inside of the coil until it reaches the desired voltage. The variac's single-coil design does not create heat like resistance-style voltage regulators. Variacs produce up to 110 per cent of its input voltage. A 240-volt variac produces voltages between zero and 264 volts.

Examine the variac's wiring diagram, located on the side of its housing. The diagram assigns a number to each terminal and lists the terminal's function. Terminal "1" connects to the input's common wire and terminal "3" connects to the load's variable output terminal. Variacs use terminal "2" when the desired output voltage exceeds the input voltage and terminal "4" for output voltages equal to or less than the input voltage.

Loosen the variac's terminal "1" nut with the correct sized hex-head screwdriver, usually 5/16- or 3/8-inch. Wrap both the input and the output circuits' common wires around the terminal and tighten the nut. Common wires usually use white-coloured insulation.

Loosen either the variac's terminal "2" or terminal "4" nut with the correct size hex-head screwdriver. Choose the terminal that matches the desired output function, as stated in Step 1. Wrap the second input wire around its respective terminal. Tighten the loose nut.

Loosen the variac's terminal "3" nut with the correct size hex-head screwdriver. Wrap the output circuit's second wire around the terminal. Tighten the loose nut.

Things You'll Need

  • Hex-head screwdriver set
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About the Author

Based out of Central Florida, Robert Sylvus has been writing how-to and outdoor sports articles for various online publications since 2008. Sylvus has been a home improvement contractor since 1992. He is a certified HVAC universal technician.