How to Wire Three-Phase Connectors

Updated February 21, 2017

Power companies commonly generate and transmit three-phase power over high-tension lines. High- power industrial equipment, factories and large buildings also often use three-phase electricity. The connectors may have four of five pins, depending on whether they need a neutral wire for the specific application. The size of the connector depends on the voltage and amperage of the circuit. Many three- phase circuits operate at 440 volts AC and require a licensed electrician to make the connections. Three-phase electricity is rarely available used in residences. .

Remove the screws or bolts holding the outer cover to the connector.

Loosen the screw or bolt connection on the terminal lug for each of the four (or five) conductors.

Strip enough insulation off the end of each so that it will go into the terminal all the way, with the insulation butting up against the terminal.

Insert each wire into its respective terminal and tighten the screw or bolt. Wiring diagrams use the letter L and a number to identify the three phases. In the United States, for 120- 208-or 240-volt systems, L1 uses a black wire, L2 uses a red wire and L3 uses a blue wire. For 277/440- volt systems, L1 uses a brown wire, L2 an orange wire and L3, a yellow wire. In either voltage system, the neutral (N) wire is white and the ground wire (G), green.

Replace the cover on the connector body and tighten the screws or bolts.


Consult the wiring diagram of the equipement your are connecting to determine whether a neutral wire is needed.

Things You'll Need

  • Wire cutters
  • Wire stripper or knife
  • Screwdriver or can wrench
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About the Author

Richard Asmus was a writer and producer of television commercials in Phoenix, Arizona, and now is retired in Peru. After founding a small telecommunications engineering corporation and visiting 37 countries, Asmus studied broadcasting at Arizona State University and earned his Master of Fine Arts at Brooklyn College in New York.