What is ATS and when do you need it

How an ATS works

1. The ATS continuously monitors the voltage of the public mains.
2. When the mains fails or the voltage drops outside the permitted limits, the ATS sends a start signal to the generator.
3. When the generator reaches stable voltage, the ATS disconnects the house from the mains and connects it to the generator.
4. When the mains returns and stays stable, the ATS switches the house back to the mains and stops the generator.

The changeover is not instantaneous. The house is without power until the generator has started and taken over the load. A computer or server that must not lose power even for a moment also needs a UPS.

What the generator must have

• Electric start, because the ATS starts the generator without you. A generator with manual start cannot work with an ATS.
• A built-in ATS or an ATS output (a connection for a separate ATS unit).
• A sound battery for starting. If it is flat, the generator will not start when it should.
• Fuel in the tank. The automation does not help if the tank is empty, so choose a model with sufficient run time.

Built-in ATS or ATS output

In the descriptions of the models in our range, two versions are distinguished:

• Built-in ATS: the automation is in the generator. According to the product description, these are the KS 7000E ATS and KS 4000iE S ATS.
• ATS output or connection: the generator is prepared for a separate ATS unit that is installed next to the household distribution board. Examples are the KS 5500iE S ATSR, KS 8100iE ATSR and KS 9200HDES-1/3 ATSR.

Before buying, check in the product description which version the model has and what is needed for connection. If you are not sure, ask us.

Examples from our range

Prices are valid at the time of writing (October 2026); the current price is on the product page.

For backup power, run time matters too. At 50% load the KS 7000E ATS runs for about 17 h, the KS 6100IDE ATSR about 19 h and the KS 9200HDES-1/3 ATSR about 11.1 h.

When you need an ATS

• A well pump, pressure booster pump or drainage pump that must run even when you are not at home.
• Heating (a boiler, a circulation pump) in winter, when a house or holiday home must not be left without heating.
• Refrigerators and freezers with food or medicines.
• An alarm, cameras and lighting.
• A small office, surgery or shop where every interruption costs money.

If you only start the generator occasionally and are always next to it, an ATS is not necessary. A manual mains/generator changeover switch installed by an electrician is then enough.

Connecting to the house installation

A generator, with or without an ATS, may be connected to the house installation only by an authorised electrician. They install a changeover switch (ATS or manual) that at every moment keeps the house connected either to the mains or to the generator, never to both.

Without a changeover switch, current from the generator can flow into the public mains (backfeed). This is dangerous for workers repairing the network, and it can also damage the generator when the mains returns. So never connect a generator to the installation through a socket.

The electrician will also check which circuits the generator may supply, given its output. Estimate how much power you need in the power calculator.

Maintaining a generator with an ATS

• Start the generator under load now and then, as the manufacturer's instructions say, to check that everything works.
• Check that the battery is charged.
• Keep the tank full and watch out for old fuel.
• Change the oil and filters according to the running hours in the manual.