How to wire a three-phase light switch

Written by g.k. bayne
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How to wire a three-phase light switch
(Comstock/Comstock/Getty Images)

Three-phase light switches control power to three-phase electrical devices. Typically, the switches are used to control special three-phase lighting and small electrical motors. Three-phase power is usually employed in industrial settings, not home electrical systems. Labelling on three-phase switches is very specific and must be followed for correct operation to the devices connected, especially electric motors. The National Electrical Code (NEC) regulates all wiring practices and Article 430 is specific for all three-phase motor wiring.

Skill level:

Things you need

  • Wire strippers
  • Screwdriver

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  1. 1

    Shut off all three-phase electrical power to the device to which you are attaching the switch. This may entail turning off the circuit breaker or pulling the fuses that supply power to the device.

  2. 2

    Strip the ends of the wires that are to be attached to the three-phase switch screw terminals. Remove approximately ¾- inch of the outer insulation to reveal the bare copper.

  3. 3

    Identify the wires coming from the main electrical panel for the three-phase power. Low voltage, 240-volt, three-phase electricity is generally identified by three wires coloured black, red and blue. High voltage, 480-volt, three-phase power is identified by brown, orange and yellow wires --- one each --- for a total of three.

  4. 4

    Connect the wires coming from the main electrical panel to the screw terminals on the three-phase switch. Low-voltage connections will be secured as follows: black to L1, red to L2 and blue to L3. The high-voltage screw terminal connections are brown to L1, orange to L2 and yellow to L3.

  5. 5

    Identify the wires going to the device. In all cases for electrical wiring, the wires are labelled T1, T2 and T3. The wires may be the same colour as the wires coming from the electrical panel. Connect the wires going to the device, to the screw terminals on the switch labelled T1 to T1, T2 to T2 and T3 to T3. If the low-voltage wires are not labelled, you connect black to T1, red to T2 and blue to T3. High-voltage device wires are brown to T1, orange to T2 and yellow to T3.

Tips and warnings

  • Follow all local electrical regulations because these may supersede NEC regulations.
  • You will never have different voltages connected to the same three-phase light switch.

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