Automatic Transfer Switches for Home Generators
An automatic transfer switch for generators senses when utility power drops, tells your standby generator to start, and moves the house load over without anyone touching a breaker. It's the right choice when you own (or are buying) a standby generator, and it's usually the wrong one for a portable generator that can't start itself.
Installed, an automatic switch typically runs $600 to $2,500. The generator, the wiring and the permit are what make the full project expensive.
How an automatic transfer switch works
The switch has a controller that watches the utility voltage. The sequence goes like this:
- Utility power drops, and the controller confirms it's a real outage, not a flicker.
- It signals the standby generator to start. Generac says its units start within seconds of sensing an outage.
- Once the generator is up to speed and voltage, the switch moves the load from utility to generator.
- When utility power returns and holds steady, the switch moves the load back, and the generator runs a short cool-down before it shuts off.
The switch is mechanically built so it can only be on one source at a time. That's what protects line workers working on the downed line, and it protects your generator when the grid comes back.
Who it's for
Get an automatic switch if:
- You have a natural gas or propane standby generator, or you're pricing one. See standby generators.
- Someone in the house can't be left to run a generator by hand, or you travel and the sump pump has to keep running.
- You want the whole house, or most of it, backed up.
Skip it if you own a portable generator. Most portables have no way to start themselves on a signal, so an automatic switch has nothing to talk to. A manual transfer switch or interlock is the honest fit, and much cheaper.
Types and sizes compared
The main choice is whether the switch is service-entrance rated (SER). An SER switch includes the main service disconnect, so it can go between the meter and your panel and carry the whole house. A non-SER switch goes after your existing main breaker and usually feeds a separate panel of chosen circuits.
| Option | Where it goes | What it backs up | Notes |
|---|---|---|---|
| SER automatic switch | Between meter and main panel | Whole house | Generac offers SER units from 100 to 400 amps |
| Non-SER automatic switch | After the main breaker | Selected circuits or whole panel | Generac also lists non-SER units from 100 to 800 amps |
| Essential-circuit switch with load center | Beside the main panel | A set group of circuits | Generac lists a 16-circuit essential version |
| Switch with integrated meter base | At the meter | Whole house | Generac sells these in 150- and 200-amp sizes |
For a whole-house switch, the rating has to match your service size, which is printed on the main breaker. HomeGuide prices a 200-amp switch at $680 to $1,500 before installation. A 400-amp switch runs $1,800 to $3,200 for the unit alone, and only makes sense if your service is that large.
Bigger isn't automatically better. A whole-house switch on a generator that can't carry the whole house means the central air and the range can overload it. That's why some systems add load management, which holds off big loads until the generator has room for them. Ask your installer whether the switch you're quoted includes it.
Cost to install
| Item | Cost |
|---|---|
| Automatic switch, installed | $600 to $2,500 |
| Automatic switch, unit only | $400 to $2,000 |
| Installation labor | $200 to $500 |
| Electrical permit | $50 to $350 |
| Wiring labor to connect a whole-house generator | $3,000 to $5,000 |
| Panel replacement, if needed | $520 to $2,100 |
Angi puts electrician labor at $50 to $100 an hour, with most transfer switch installs taking two to four hours. HomeGuide's electrician range runs to $130 an hour plus a call-out fee. The switch is usually bundled into a standby generator quote, so ask for it as its own line. See standby generator installation and standby installation cost for the full project.
Brands you'll run into
Most homeowners end up with the switch made by their generator's manufacturer, because the controller has to talk to the generator. Generac, Kohler and Briggs & Stratton each sell switches matched to their standby units. Eaton and ASCO make automatic switches too, with ASCO mostly known for commercial and industrial gear.
APC shows up in searches for "automatic transfer switch," but those are rack-mount units that switch computer equipment between two power feeds. They're not home generator switches.
Solar, batteries and portable generators
Battery backup systems handle their own switching. The battery maker's gateway or backup panel isolates the house from the grid during an outage, so you don't add a separate generator-style switch unless the battery maker's install guide calls for one. See home batteries.
Portable generators are the gray area. Generac's HomeLink manual switches can be upgraded for automatic use, but only with Generac home standby generators up to 11 kW. If a seller pitches an automatic switch for a portable, confirm the generator has remote auto-start and that the switch is listed for that pairing.
How installation goes
The electrician mounts the switch near the meter or main panel, runs the feeder and control wiring to the generator pad, and connects the controller. With an SER switch, the utility often has to pull the meter, so expect an appointment. Then the inspector checks the job against the manual and local code.
Generac recommends an authorized dealer or licensed contractor for installation. After that, keep up with service. Generac recommends servicing the generator every six months, and the switch gets checked during that visit.
FAQ
How long does it take for an automatic transfer switch to work?
The generator starts within seconds of sensing an outage, per Generac. The switch then waits for the generator to reach stable voltage before moving the load. Expect a short dark period, not instant power. For computers that can't blink, add a UPS.
What is an ATS in electrical terms?
ATS stands for automatic transfer switch. It's a switch with a controller that moves your electrical load between utility power and a backup source on its own. It's mechanically interlocked so both sources can never be connected at once.
Where can I find the manual for my Kohler automatic transfer switch?
Look for the model and serial number label inside the switch door, then search that model on Kohler's power website or ask your Kohler dealer. The installation and operation manuals are matched to the model, and the dealer that installed it should have a copy on file.
What is a Kohler transfer switch?
It's Kohler's automatic transfer switch, built to work with Kohler home standby generators. Like other brands, its controller signals the generator to start and moves the load when the utility drops. Pairing a Kohler generator with another brand's switch usually means losing features, so most installers keep them matched.
Can I install an automatic transfer switch myself?
It involves the service entrance, where the utility conductors stay live. Hire a licensed electrician. Most areas require a permit and inspection, and Generac recommends a licensed contractor or authorized dealer.
Sources
- AngiHow Much Does It Cost to Install a Generator Transfer Switch? (opens in a new tab)
- HomeGuideGenerator Transfer Switch Installation Cost (opens in a new tab)
- GeneracStandby Generator Transfer Switches (opens in a new tab)
- GeneracHome Standby Generator FAQ (opens in a new tab)
- GeneracHomeLink Transfer Switches (opens in a new tab)