How to Wire a Generator Transfer Switch

Written by g.k. bayne
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Installing a transfer switch for a full household generator may be a mandatory requirement from your local electrical utility. Connecting the wires for the three position switch can be accomplished once you have the properly sized wires. You should check with local electrical codes for proper location of the generator switch and the size of the wires for the installation, as local codes may vary from state to state. By following a basic process, you can wire a generator transfer switch in a few short hours.

Skill level:

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Things you need

  • Generator transfer switch
  • Allen wrenches
  • Socket set
  • Pocket knife
  • Screwdriver (Phillips and flat head)

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  1. 1

    Turn off the power from the utility provider before attempting any type of main electrical power wiring.

  2. 2

    Open the door on the transfer switch and observe the Allen lug connectors or the bolt heads where the wires are to be terminated. There are six termination points on the switch itself, along with three grounding screw terminals and three ground or neutral terminals. The grounding screw terminals will be directly connected to the frame of the switch. The six termination points and ground or neutral terminals will be described in the connection process.

  3. 3

    Strip back one inch of the insulation covering on all of the wires. You should have four wires each that come from the following locations: the generator itself, the power utility meter, and the circuit breaker box. The four wires are, one grounding conductor or earth ground, one ground or neutral wire and two power wires.

  4. 4

    Connect all three of the grounding wires to the grounding bar mounted to the rear of the transfer switch. Use either the Allen wrenches or the proper socket depending on the termination configuration.

  5. 5

    Attach the ground or neutral wires to the ground connection bar. This bar may also be tied to the rear of the transfer switch. Different manufacturers may have various methods for this connection. On new switches, there will be an identification tag for the correct ground bar.

  6. 6

    Connect the two power wires that are going to the household panel circuit breaker box to the two centre lugs on the transfer switch. These sets of lugs are permanently connected to the two large knife blade connectors.

  7. 7

    Terminate the wires that are coming from the power utility meter to the two lower set of lugs on the transfer switch unless dictated differently from the electrical utility. Generally, the normal operation of the transfer switch will be in the up position, which engages the lower lugs with the large knife blade switch.

  8. 8

    Attach the final two wires from the generator to the two top lugs on the transfer switch. This will complete the main power wiring.

  9. 9

    Connect the start/run wires from the generator, if provided, to the auxiliary contact screw terminal mounted on the side of the transfer switch with the screwdriver. Not all transfer switches have this remote start/stop contact block. There will be only two wires provided from the generators manufacturer if this option is provided.

Tips and warnings

  • Check with all state and local electrical codes whenever installing any electrical device.
  • Some generator manufacturers may require only licensed electricians to perform the transfer wire terminations due to warranty issues.

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