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What is an Automatic Transfer Switch (ATS)?

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An automatic transfer switch is installed with a standby generator to provide the automatic operation of your generator in a power outage. The ATS will changeover from mains to generator supply automatically to keep power maintained to your home or business without any manual interaction needed.

How does an automatic transfer switch work?

The automatic transfer switch (ATS) will monitor your incoming mains supply to your home or business and when power is lost it will send a signal to start your standby generator. Once your standby generator is running and producing adequate power, the automatic transfer switch will automatically change over to the generator supply and feed your circuits from the generator.

When the mains returns, the automatic transfer switch will monitor the mains for a short period of time (approx. 5-10 minutes) to ensure that it is stable, before changing the feed back from the generator to the incoming mains from the grid.

Once you are back on mains supply, there will be a cooling period that allows your engine to cool down  before shutting the generator down, leaving it in standby operation waiting for the next outage.

Where to install an automatic transfer switch?

An automatic transfer switch is installed usually indoors and close to the incoming mains supply.

The panel will be installed between the mains supply and your mains switchboard or consumer unit.

During normal operation with mains healthy, the panel will feed your switchboard or consumer unit as usual from the mains, but during a power outage the automatic transfer switch will start and feed the consumer unit or switchboard from the generator instead.

How much is an automatic transfer switch?

Automatic transfer switch panels vary in cost, depending on the switchgear installed and the type of controls or control unit used.

The rating or size of the panel required will also determine the costs. Eg a 63Amp panel will be much cheaper than a 200Amp panel.

Basic ATS panels use contactors and timer relays and these panels can be purchased from as little as £400-500.

More advance automatic transfer switch panels can use panel mounted control unit such as deep sea and comap, which have higher functionality such as load measurement, load shedding, programmable alarms and remote cloud based monitoring.

More complex panels as above, especially larger rated can be in excess of several thousand pounds!

What size automatic transfer switch do I need?

The size of automatic transfer switch you will need will depend on the rating of your generator and also the size of the mains supply.

Generally you will size the automatic transfer switch to the rating of the mains supply, as your panel will need to be rated for the maximum load current on your mains supply.

For example, if you had a 100Amp incoming fuse, you will need a 100Amp minimum automatic transfer switch panel.

How to install an automatic transfer switch?

It is important that whoever installs your automatic transfer switch is a competent and qualified electrician.

Your mains will need to be switched off and isolated to install an automatic transfer switch, as your incoming mains feed into your switchboard will be wired through the mains contactor or switch inside your switch panel.

Your generator will be wired into the generator terminals inside your automatic transfer panel and this will allow either the mains or generator to supply the load side which feeds into your switchboard or consumer unit incomer.

There are other control wires that will need to be taken from the automatic transfer panel into your generator for the remote start and also a small power supply for the standby generator battery charger or water heater circuits.

Most automatic transfer panels will be supplied with wiring diagrams to assist with the connection of the cabling.

Where to buy an automatic transfer switch?

Automatic transfer switches are specialized electrical control panels, and the manufacture and supply of these should be limited to competent critical power specialists.

We do not recommend using unknown brands or budget/cheap automatic transfer panels as they can fail or provide a fire risk if not certified and good quality products.

Remember that if this panel fails, you will lose power to your entire facility until the fault can be repaired. It is important to buy a panel that has recognized parts.

Some of the better units have a manual bypass, which allows you to switch it over manually if a component fails and your system does not work automatically. This is a desirable feature in our opinion.

Automatic transfer switch Vs manual

You can choose to have a manual transfer switch as an alternative to an automatic transfer switch.

A manual transfer switch is used when a power outage occurs, the generator is started manually and then the switching is done manually by the user.

The obvious advantage of having an automatic transfer switch is that no manual interaction or operation is necessary.

Also, as power outages can happen out of normal hours or in the night, it means that they operate 24/7 and there is very little delay to restore the power.

Solent Power are critical power specialists and can provide expert advice and support with your standby generator and automatic transfer switch requirements.

If you need any support or advice with the supply, installation or testing of your equipment please feel free to get in touch with our team

Paul Phelps Solar Power Owner
Paul Phelps
Paul is the MD of Solent Power and specialises in emergency power solutions, helping to protect your facilities from power loss. Get in touch with us today to discuss the different power brands that we can offer and how they can suit your needs.
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