Generators
Automatic Transfer Switch (ATS) Explained: How Generators Start Themselves
Short answer
An automatic transfer switch (ATS) senses when mains power fails, signals the generator to start, switches your loads to generator power, and switches back when the grid returns. It also prevents the generator from back-feeding the grid, which is dangerous. An ATS makes a standby generator hands-free and safe.
How it works
- The controller monitors mains voltage.
- If it fails or goes out of range, it waits a short delay and starts the generator.
- When the generator output is stable, the switch moves loads to it.
- When mains returns and is stable, loads transfer back.
- The generator cools down and stops.
Why it matters
- Back-feeding the grid can electrocute linemen and damage equipment; an interlocked transfer switch prevents it.
- Servers, fridges, security systems and businesses benefit from fast, automatic switchover.
- Manual changeover works but needs someone present.
Choosing one
- Match the current rating and number of phases to your supply.
- Decide whether to back up the whole building or an essential-loads board.
- Check the controller supports your generator.
Related
See generator sizing and our generator installation service.
Common questions
Can I connect a generator directly to my board?
Not without an approved changeover or interlock. Direct connection risks back-feeding and fire.
How fast does an ATS switch?
Typically within seconds, after the generator starts and stabilises.
Do I need an ATS with solar?
Hybrid systems have their own switching. A generator can be integrated through the inverter or a separate ATS depending on the design.