How to Install a Portable Generator Transfer Switch

A portable generator with a cord coming out the front.
  • 10 hours
  • Advanced
  • 1,000
What You'll Need
10/4 Extension cord
Transfer switch panel
10/4 cable
220-V 30 Amps breaker
New breakers if the two panels are different
Side cutters
Wire stripper
Wire nut connectors

A portable generator transfer switch will transfer power to selected circuits in the event of a power outage. Once installed, you’ll simply need to plug in your portable generator and crank it up. Everything in the new circuit box—or portable generator transfer switch—will run.

For anyone used to working with electricity, this isn’t a complex task. However, novices should get experienced help before attempting to install a portable generator transfer switch because of the serious dangers involved in working with electricity.

Step 1 - Buy a Generator

Before installing a portable generator transfer switch you need to know what size generator to buy. How much do you really need to run during a power outage? Look at the wattage of your appliances and buy a generator that allows for a comfortable margin above this to accommodate potential spikes in energy consumption.

Step 2 - Shut Off Power

Shut off power to the main breaker panel and remove the cover to expose the insides. Remember that the main disconnect at the top will still be hot so avoid approaching it.

hands flipping switch on circuit breaker

You’ll see a large knockout on the side of the box. Remove it and put in a threaded nipple securing it with the proper nuts. Attach the new box the same way at the other end of the nipple. Use heavy screws to anchor the new box to the wall next to your main circuit panel. Now attach the grounding bus to the wall of the new panel.

Step 3 - Wire It

Select ahead specific circuits that will be needed during an outage such as lighting, water pump, and appliances. The goal is to attach those specific circuits to new circuit breakers inside the new panel so that if there is a power outage, the main breaker in the new panel can be switched over so that all three lines from the main panel are cut off and isolated from those selected circuits which are then connected and supplied directly from the generator output.

Man working on electrical panel

Safety Note: Turn OFF the main breaker of the main panel to avoid serious risk of electrical injury.

You can then remove the black and red wires from each of the breakers feeding the selected circuits and the corresponding neutral and ground wires from their busbars, and pull them out from the main panel, then transfer them over into the new transfer switch panel. Use an insulated screwdriver for this.

Insert a 30 Amps 220 Volts circuit breaker in one of the newly created spots in the main panel. Strip the sheathing from 10/4 cable and feed it through the conduit between the two boxes. Connect the white and green wires to the appropriate buses in the main panel.

Now attach the red and black wires from the 10/4 cable to this 30 amps breaker. Those same wires now need to be connected in the transfer switch panel, connecting each of the Black, Red, and White (neutral) wires to three different breakers, each one identifying the wire color assigned to it. With this done, the ground wire must be connected to its busbar, and another ground wire must connect the two panels together.

man screwing wire into circuit breaker

Those breakers are stacked side by side and mechanically connected together and also to three more breakers exactly opposite (altogether forming a six-pack), so if switched one way or the other, all six breakers switch at once. This way, when three from one side are turned OFF, the three from the other side are ON. The generator's 10/4 220-V feed line will be connected to those last three breakers (just opposite to the ones connected to the main panel) and routed to where the generator outlet will be on the exterior wall of the house, next to the generator.

Step 4 - Extend the Wires

Switching wiring over could result in some of them being too short to reach their new location, in which case terminal boxes will need to be installed, into which an extra length of wire will be connected to the short piece using wire nut connectors, making it long enough to complete the circuit to their new circuit breaker. just keep matching the colors of the wires when hooking them up.

Step 5 - Set Up Outlets

To set up an outlet for the portable generator to plug into the transfer switch, you’ll need a 10/4 cable running from the transfer switch panel to where you want your outlet to be outside the house and probably close to the generator.

man screwing in wall outlet

Mount the outlet box to the house and drill a hole through the side of the house to put the wiring through. Connect to the receptacle for the generator, the black and the red to the brass terminals and the white to the silver, and of course the ground wire to the green terminal screw and also to the electrical box.

Test the newly install transfer switch by switching over the main six circuit breakers. All the selected emergency circuits are now without power. Plug in the generator and run it to restore power to those circuits.