What Is an Automatic Transfer Switch (ATS), and Why Is It Important for Your Generator?
Power cuts can happen unexpectedly, interrupting essential equipment, heating systems, refrigeration and everyday business operations. A backup generator provides an alternative source of electricity, but what happens if the power fails when nobody is available to start the generator or switch the power supply?
This is where an Automatic Transfer Switch (ATS) becomes particularly useful.
An ATS allows a compatible backup generator system to respond automatically to a mains power failure, reducing the need for manual intervention and helping minimise downtime.
But how does an automatic transfer switch work, and do you really need one for your generator?
What Is an Automatic Transfer Switch (ATS)?
An Automatic Transfer Switch (ATS), also known as an automatic changeover switch, is a device designed to automatically transfer an electrical load between the main electricity supply and a backup power source, such as a generator.
Under normal conditions, the building receives electricity from the mains supply. When a power failure occurs, the ATS detects the interruption and, when connected to a compatible generator with an automatic starting system, allows the backup power system to take over.
Once the mains electricity supply is restored and stable, the ATS transfers the electrical load back to the normal power source. One of its most important functions is ensuring that the mains supply and generator are not connected to the load simultaneously, helping prevent dangerous electrical backfeeding.
How Does an Automatic Transfer Switch Work?
An ATS operates through a sequence of monitoring, generator starting and power switching.
1. Monitoring the Mains Electricity Supply
The automatic transfer switch monitors the incoming electricity supply. If the mains power fails or, where supported, the voltage moves outside acceptable operating limits, the system detects the problem.
2. Starting the Backup Generator
When a power failure is detected, the ATS system can send a starting signal to a compatible generator equipped with the necessary automatic start controls.
Important: Not every generator supports automatic starting. The generator must have the appropriate capabilities and be correctly configured to work with the ATS.
3. Transferring Power to the Generator
Once the generator starts and its electrical output stabilises, the ATS transfers the connected load from the mains electricity supply to the generator.
This allows the generator to supply electricity to the circuits and equipment included in the backup power installation.
4. Returning to the Mains Supply
When the normal electricity supply returns and is stable, the ATS automatically transfers the load back to the mains.
With a compatible generator control system, the generator can then shut down automatically, potentially following a cooling period where supported.
The entire process reduces the need for manual switching, although a short interruption in electricity supply will normally occur during the changeover.
Why Is an ATS Important for Your Backup Generator?
An automatic transfer switch offers several practical advantages for homes, businesses, workshops and other properties that depend on a reliable electricity supply.
Automatic Backup Power
Without an automatic transfer system, someone normally needs to start the generator and operate a manual changeover switch when the mains electricity fails.
An ATS simplifies this process by automatically switching between power sources when installed with a compatible generator system.
This can be especially useful during overnight power cuts or when a property is unattended.
Reduced Downtime
Even a short power interruption can disrupt business operations, heating systems, refrigeration or other essential electrical equipment.
An ATS helps reduce the time spent without electricity by removing the need for someone to be present to perform the changeover manually.
However, an ATS does not provide uninterrupted power. Equipment that cannot tolerate even a brief interruption may require a suitable uninterruptible power supply (UPS) as part of the overall backup power system.
Safer Power Switching
Electrical safety is one of the most important reasons to use a correctly installed transfer switch.
An ATS is designed to isolate the generator supply from the mains supply during changeover, helping prevent backfeeding electricity into the public distribution network.
Backfeeding can create serious risks for electrical workers and may damage equipment.
A properly selected and professionally installed transfer switch is therefore an essential part of a safe generator-to-building connection.
Greater Convenience
With a compatible automatic backup power system, there is no need to manually switch the electrical supply every time a power cut occurs.
The ATS also handles the return to mains electricity when the normal supply is restored.
This is particularly convenient for properties where the generator may need to operate while the owner or operator is away.
Better Management of Generator Operation
Depending on the generator and control system, an automatic backup installation may support functions such as starting delays, engine warm-up and cooling periods before shutdown.
These functions can help manage the generator's operating sequence, but they should not be assumed to be included with every ATS.
When Is an Automatic Transfer Switch Particularly Useful?
An ATS can be valuable wherever a power interruption causes inconvenience, equipment downtime or disruption to essential operations.
Homes and residential properties: An automatic generator system can help maintain power to selected circuits serving heating controls, refrigeration, water pumps and other essential household equipment.
Workshops and businesses: A backup generator with an ATS can reduce disruption to suitable electrical equipment and help businesses resume operations following a power failure.
Commercial premises: Refrigeration, communications equipment and other important systems may benefit from an automatically activated backup power supply.
Unattended properties: Where nobody is available to start the generator or manually change the power source, an automatic transfer system can provide additional convenience.
The suitability of an ATS depends on the electrical installation, the equipment being supplied and the capabilities of the generator.
Can You Use a Generator Without an ATS?
Yes. An automatic transfer switch is not essential for every generator installation.
A generator can be operated without an ATS using an appropriately rated manual changeover switch installed by a qualified electrician.
With a manual system, someone must start the generator and switch the electrical load between the mains supply and the generator.
This may be a practical option where power cuts are infrequent or automatic operation is not required.
However, a generator must never be connected to a building's electrical installation using a double-ended plug cable through an ordinary socket.
This dangerous method can feed electricity back into the mains network, creating a serious risk of electric shock, fire and equipment damage.
Whether you choose an automatic or manual changeover system, safe electrical isolation and professional installation are essential.
How to Choose the Right ATS for Your Generator
Not all automatic transfer switches are suitable for every generator. Before selecting an ATS, several important factors should be considered.
Generator Compatibility
The ATS must be compatible with the generator's control system and connection requirements.
Some generators have dedicated ATS connections, while others may support remote-start control through suitable interfaces.
Having an electric starter alone does not necessarily mean that a generator can operate automatically with an ATS.
Single-Phase or Three-Phase Supply
The transfer switch must be suitable for the electrical system being connected, whether it is a single-phase or three-phase installation.
The generator, ATS and building's electrical installation must be correctly matched.
Electrical Load and Current Rating
The ATS must be appropriately rated for the electrical load it will transfer.
Current ratings such as 32 A, 63 A and 100 A may be encountered, but the correct selection depends on the installation and its electrical requirements.
A qualified electrician should assess the necessary rating, switching arrangement and protective devices.
Generator Type and Control Requirements
Diesel, petrol and other generator systems may use different starting and control arrangements.
Before purchasing an ATS, confirm that the generator supports the required automatic control functions and that the selected device is suitable for the intended application.
Unicraft Automatic Transfer Switch for Diesel Generators
For owners of compatible Unicraft diesel generators, the Unicraft Automatic Disconnector (Art. 6731999) offers a dedicated automatic mains isolation solution.
The device is designed for use with selected Unicraft PG-D TEA-S HC synchronous diesel generators, allowing the generator to be connected to a building through an automatic mains isolator switch instead of a manual disconnector.
Compatible Unicraft Generator Models
The Unicraft Automatic Disconnector 6731999 is compatible with the following models:
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Unicraft PG-D 150 TEA-S HC
The device connects to the generator through an Aviation GX 20, 6-pin ATS plug, and a 2-metre connection cable is included.
Correct installation and system configuration are essential. All electrical connections to a property must be completed by a qualified electrician.
View the Unicraft Automatic Disconnector (ATS) – Art. 6731999
Is an Automatic Transfer Switch Worth It?
If you rely on a backup generator and want to reduce the need for manual intervention during power cuts, an ATS is worth considering.
It offers automatic switching between mains and generator power, helps minimise downtime and supports safer electrical isolation when correctly installed.
For homes, workshops and businesses in Ireland, the right combination of a compatible generator and automatic transfer switch can make backup power more convenient and practical.
Before purchasing, it is important to verify compatibility, understand the electrical requirements and ensure that the system is professionally installed.
A generator provides backup electricity. An ATS helps make the changeover automatic.
Explore the Unicraft Automatic Disconnector (ATS) at Millennium Machinery, or browse our range of power generators available in Ireland to find equipment suited to your power requirements.
For advice on generator compatibility and suitable equipment, contact the Millennium Machinery team.
