Automatic Transfer Switch for Generators: How It Works, Sizing and Installation
Quick answer: An automatic transfer switch (ATS) watches the mains supply. When power fails it signals an auto-start generator, waits for it to stabilise, then switches your load to the generator; when mains returns it switches back and lets the generator cool down and stop. It also prevents back-feeding the grid. You need an auto-start (electric start) generator and an ATS rated for your supply and current. H-TECH stocks the DAYLIFF DG6000DS 4.5 kVA diesel generator with ATS from KSh 247,950.
Key facts
- Detects mains failure
- Starts the generator
- Switches load safely
- No back-feeding
On this page
How an ATS Works
- Mains fails or drops out of range.
- After a short delay (to ignore brief blips) the ATS sends a start signal.
- The generator starts and warms up; the ATS checks its voltage and frequency.
- The ATS transfers the load to the generator.
- When mains is back and stable, it transfers back, then runs the generator unloaded to cool before stopping it.
ATS vs Manual Changeover
| Manual changeover switch | ATS | |
|---|---|---|
| Who switches | A person | Automatic |
| Generator | Any (pull or key start) | Must be electric/auto start |
| Time without power | Until someone acts | Seconds |
| Best for | Homes with occasional outages | Water plants, milk chillers, clinics, shops, homes with frequent outages |
Generators and Protection at H-TECH
DAYLIFF DG6000DS 4.5 kVA Diesel Generator with ATSKSh 247,950
DAYLIFF DG7500P 6 kVA Petrol GeneratorKSh 123,980
DAYLIFF DG3800ST 2.8 kVA Petrol GensetKSh 50,370
DAYLIFF DG1200S 1 kVA Petrol GensetKSh 26,100
DAYLIFF Automatic Voltage Switcher 3PKSh 16,310| Product | Price |
|---|---|
| DAYLIFF DG6000DS 4.5 kVA Diesel Generator with ATS | KSh 247,950 |
| DAYLIFF DG7500P 6 kVA Petrol Generator | KSh 123,980 |
| DAYLIFF DG3800ST 2.8 kVA Petrol Genset | KSh 50,370 |
| DAYLIFF DG1200S 1 kVA Petrol Genset | KSh 26,100 |
| DAYLIFF Automatic Voltage Switcher 3P | KSh 16,310 |
Current listed prices incl. VAT (updated 10 November 2026).
Sizing
- The ATS current rating must match or exceed the supply and the generator output.
- Single-phase and three-phase ATS units are different; match your supply.
- Size the generator for the loads it will carry: see the generator size calculator.
- Equipment such as milk chillers and RO plants benefits from voltage protection too: see automatic voltage switchers.
Installation Checklist
- Installed by a qualified electrician between the meter/main switch and your distribution board.
- Generator neutral and earthing arranged correctly.
- Control cable from ATS to the generator's auto-start terminals.
- Test monthly by switching off the mains.
Safety: electrical connections must be made by a qualified electrician, with correct earthing and a breaker sized for the equipment.
Frequently asked questions
What does an ATS do on a generator?
It starts the generator when mains fails and switches your load over, then back when mains returns.
Can I use an ATS with any generator?
Only with an electric/auto-start generator that accepts a remote start signal.
What is the difference between an ATS and a changeover switch?
A changeover switch is operated by hand; an ATS works automatically.
How long does an ATS take to switch?
Usually seconds to a minute, including generator start and warm-up delays set on the controller.
Do I need an electrician to install an ATS?
Yes. Wrong wiring can back-feed the grid and is dangerous.