How to Wire Three-Phase Connectors

Written by richard asmus
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How to Wire Three-Phase Connectors
Power lines run on three-phase electricity. (three old transformers image by leemarusa from

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. .

Skill level:

Things you need

  • Wire cutters
  • Wire stripper or knife
  • Screwdriver or can wrench

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  1. 1

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

  2. 2

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

  3. 3

    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.

  4. 4

    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.

  5. 5

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

Tips and warnings

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

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