How to Wire a Potential Transformer


Potential transformers let metering devices measure high-voltage power sources that it otherwise could not handle. A potential transformer performs like an accurate step-down transformer. The high-voltage side of the transformer wires directly to a voltage source, and a metering device connects to the low-voltage side. This allows technicians to monitor dangerous high-voltage circuits without exposing themselves to the circuit. A potential transformer's low-voltage side does not have the ability to withstand high-current loads like a typical step-down transformer. A potential transformer's low-current load is relatively small in size when compared to a standard step-down transformer.

Things You'll Need

  • Flat-head screwdriver
  • Metering device
  • Inspect the potential transformer's wiring guide. Identify the color-coded high-voltage wires and the maximum input-voltage rating. Identify the color-coded low-voltage wires and the output voltage. The potential transformer's high voltage side must connect to a power source below its maximum rating. The wiring guide also states the potential transformer's ratio.

  • Turn the high-voltage power source off, if possible. Usually the power source will have a circuit breaker labeled "Main."

  • Inspect the power source's terminal block. Single-phase equipment uses two hot terminals--"L1" and "L2"--and three-phase equipment uses three hot terminals--"L1" "L2" and "L3." The terminal block provides a convenient place for a potential transformer to connect to the power source.

  • Connect the potential transformer's color-coded high-voltage wires to the power source's terminal block. Connect the wire labeled "L1" to the "L1" terminal, the "L2" wire to the "L2" terminal and, if used, the "L3" wire to the "L3" terminal. If the terminal block uses retaining screws to hold the wires in place, then loosen the terminal block's retaining screws with a flat-head screwdriver, slip each of the potential transformer's high-voltage wires into its respective terminal and tighten the retaining screws. If the terminal block uses wire connectors, then slip each of the potential transformer's wires into its respective connector.

  • Connect the metering device to the transformer's low-voltage terminal screws. Often the device screws directly to the transformer's terminals. If the device requires wire between the transformer and the device, then use the shortest wire possible and wrap the wire around the terminal screw before tightening the screw.

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  • Photo Credit High Voltage Transformer image by Andrzej Thiel from
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