Transfer switches for generators: manual vs automatic

The short version

A transfer switch has two inputs and one output. One input is the utility. The other is the generator. The output goes to the circuits you want to keep running. A mechanical interlock inside the switch makes it impossible to connect both inputs at once, so the generator cannot feed power back onto the street. That is the same safety goal as an interlock kit, reached with a different box.

Two main types

Manual transfer switch. A small panel with its own breakers, wired next to the main panel. Each breaker is a circuit you picked. During an outage you plug the generator into an inlet, start it, and flip the switch to generator. A published cost guide lists installed prices at about $400 to $1,300 as of October 2026.

Automatic transfer switch (ATS). It watches the utility voltage. When power drops, it signals a standby generator to start, then moves the load over in seconds. When power returns it moves back and shuts the generator off. The same guide lists $600 to $2,500 installed for the switch. The generator is extra. Permanently installed generator hookup labor runs about $1,500 to $3,000, covered on the standby generator hookup page.

See the full range on the transfer switch cost page.

Which circuits to put on it

Pick by what hurts when it is off, then check the wattage. Start with the refrigerator, a freezer if you have one, furnace fan, a handful of lights, the garage door opener, internet and phone chargers. A well pump or sump pump belongs on the list if you have one. Air conditioning and electric ranges usually do not fit a portable generator. A load calculation is how the electrician adds up the watts so the generator is not asked to carry more than it can.

Starting a motor draws far more power than running it. A refrigerator may need three times its running watts for a second. The generator has to handle that spike, so size by startup watts for the biggest motors.

A switch versus a subpanel

A transfer switch moves existing circuits. That means the electrician rewires those circuits to pass through the switch. A critical loads subpanel does the same job in a different layout: the chosen circuits are moved to a new small panel that is fed from the main panel normally, and from the generator or battery in an outage. Subpanels cost more but handle batteries and generators the same way.

What the install includes

• The switch or panel mounted near the service
• Rewiring the selected circuits through it
• A power inlet or a hardwired connection to a standby unit
• Labels at the service equipment
• The permit and inspection

Ask which of these your quote includes. Some bids leave out the inlet or the labels.

What affects the price

• Number of circuits. Each one is another wire to reroute.
• Distance between the panel and the switch.
• Whether the work is inside a finished wall or in a garage with open framing.
• Automatic versus manual.
• Panel capacity. If the main panel is full or old, a panel upgrade may come first.

Permit

A transfer switch is a change to the home’s service wiring. Cities usually require an electrical permit and an inspection. A licensed C-10 electrician applies, and the inspector confirms the lockout, labels and wire sizes. Steps differ by city, so the building department’s page is the final word. See electrical permits in Southern California.

Use safely

Run a generator outdoors only, away from windows and doors. Fuel it when it is cool. Never connect it by a cord with two plugs to a wall outlet. Utilities warn that this can push power onto the lines and hurt line workers, and a transfer switch avoids the risk.

Choosing between manual and automatic

Pick manual if outages are short and rare, you will be home, and a portable generator is enough. Pick automatic if you travel, if someone at home depends on powered equipment, or if you already have a permanent generator on a gas line. An automatic switch is also the better match for a long outage because it restarts the generator on a schedule without anyone getting up at night.

Ask the electrician what rating the switch needs. Common home sizes are 30 amp, 50 amp and 100 amp. The rating should match the generator and the service, and the electrician should write it on the quote so you can compare bids on the same basis.