What happens when the power goes out
Generac breaks the sequence into steps (Generac, Mar 2025):
- The switch waits about 5 seconds to make sure the outage is real, not a flicker.
- The generator cranks and warms up, normally for 5 seconds, or 30 seconds in a cold start.
- Once voltage is steady, the switch moves the house load over.
- When utility power is back and stable, it switches the house back and the engine cools down and stops.
Best case is about 15 seconds; with extra crank attempts it can take a little over 3 minutes. The switch also physically separates the house from the utility lines, which protects lineworkers.
Whole-house or essential circuits
| Option | Whole-house switch | Essential-circuits switch |
|---|---|---|
| What it backs up | The whole panel | A chosen set of circuits, often 8–16 |
| Generator size | Must cover the full load, or use load management | Can be smaller |
| Example | Generac 22 kW with 200 A switch, $6,632 retail | Generac 10 kW with 16-circuit 100 A switch, $3,977 retail |
| Trade-off | Every room works, higher cost | Lower cost, some rooms go dark |
Retail prices from The Power Tool Store, November 2026. Our sizing guide shows which kW band each setup usually needs.
Service-rated or not
A service-entrance-rated switch sits right after the utility meter and has its own service disconnect, so it can act as the main electrical panel. A non-service-rated switch goes after your main breaker, like a subpanel. Generac says both transfer power the same way; which one you need depends on how your house is wired and on local code (Generac, Mar 2025). The dealer decides after seeing your meter and panel.
200 A or 400 A
The switch should match the size of your electrical service. A house on 200 A service uses a 200 A switch. Larger homes with 400 A service, often with two or three AC systems, need a 400 A switch or two 200 A switches, which is one reason those jobs cost more. The cost guide lists a switch upgrade at about $1,500–4,000 (our estimate).
Load management: running a big house on a smaller unit
The electrical code gives an automatic system two options: a generator big enough for everything the switch transfers, or an automatic load-management system with the generator sized for the most it will ever let on at once. A North Carolina code interpretation of the 2023 National Electrical Code adds that, with an automatic switch, relying on you to turn things off by hand is not allowed (NC OSFM, Dec 2024).
In practice, load management means small modules that hold off a second AC, the water heater or a pool pump until there's room. Generac's system takes up to eight Smart Management Modules, each with its own priority (Norwall); Kohler sells switch packages with load shedding built in (AC Wholesalers). Ask your dealer which loads they'll manage and in what order.
Switch costs
| Option | Installed cost |
|---|---|
| Interlock kit (portable generator) | $400–850 |
| Manual transfer switch (portable generator) | $400–1,300 |
| Automatic transfer switch | $600–2,500 |
| 200 A automatic switch, unit only | $680–1,500 |
From HomeGuide (2026), national figures. With a standby generator, the switch is usually bundled into the package price. Portable options are compared in portable vs standby.
Common questions
Does a standby generator need an automatic transfer switch?
In practice, yes. The switch is what starts the generator and moves the house onto it without you. Most standby generators are sold as a package with one.
How long does it take for the power to come back on?
Generac says 15 seconds in the best case and up to about 3 minutes 14 seconds if the engine needs extra cranking (Generac).
What is a service-rated transfer switch?
One that includes a service disconnect and can serve as the home's main panel, installed right after the meter. A non-service-rated switch goes downstream of the main breaker (Generac).
Can a 22 kW generator run a house with 400 A service?
Sometimes, with load management that keeps the biggest loads from running together. The dealer should do a load calculation and tell you which appliances will be managed.
Sources & further reading
- Generac: how long a standby generator takes to start (Mar 6, 2025)
- Generac: service-entrance-rated vs non-rated switches (Mar 7, 2025)
- Norwall: Generac Smart Management Module 7006. Up to 8 modules
- AC Wholesalers: Kohler 20RCAL-200SELS with load shedding
- NC Office of State Fire Marshal: NEC 702 interpretation (Dec 1, 2024). 2023 NEC
- HomeGuide: transfer switch installation cost (2026). National figures
- The Power Tool Store: Generac Next Gen prices (Nov 2026). Generator + transfer switch
Editorial note: General planning information, not engineering or legal advice. Prices are estimates; confirm current rules with your local officials and a qualified pro.