ATS — Automatic Transfer Switch
Also known as: Automatic Transfer SwitchATSgenerator transfer switch
An Automatic Transfer Switch is the device that detects when grid power has gone out and automatically switches your home's electrical load from the grid to your backup power source (a standby generator or a battery system). When grid power returns, it switches back. Without an ATS, you have a manual transfer switch — meaning you have to physically flip the switch yourself when the grid goes down.
For mountain residents subject to PSPS, an ATS turns backup power from "useful if you're home and awake" into "useful whether you're home or not." Most standby generator installs include one. Whole-home battery backup systems (Tesla Powerwall, FranklinWH, Enphase) include their own ATS-equivalent functionality.
If you're installing backup power, you want an ATS unless budget is tight or your scope is intentionally manual (camping-style portable gen with extension cords). The ATS is what makes backup power truly automatic.
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