Automatic Transfer Switch Explained

By R.W. Hurst, Editor

An automatic transfer switch (ATS) is invaluable for maintaining a reliable power supply in unpredictable outages. By selecting the right switch, ensuring correct installation and maintenance, and observing safety best practices, you can enjoy the advantages of a backup power system and the peace of mind it brings.


Power outages can cause significant disruptions to our daily lives and business operations. Ensuring a consistent and uninterrupted power supply is crucial in today's world, which relies heavily on technology and electricity. An automatic transfer switch is a reliable solution for maintaining power during outages.

An automatic transfer switch is an essential component of any backup power system. It facilitates seamless power transfer between the primary power source and a standby generator during an outage. By doing so, the ATS helps maintain a continuous flow of electricity, safeguarding homes and businesses from the negative impacts of power loss.

When choosing an appropriate automatic transfer switch, factors like generator power capacity, load type, and intended application play a significant role. Consulting with an electrical switchgear expert is a wise step in making an informed decision. Consider the voltage and amperage ratings and whether the switch is intended for residential, commercial, or industrial use. Switchgear systems may offer varying features, such as remote monitoring and built-in diagnostics, which cater to different requirements.

Automatic transfer switches and manual transfer switches differ in their mode of operation. While a manual transfer switch necessitates physical engagement by an individual to shift the load between the main power source and the backup generator, an ATS performs this task automatically, ensuring a more efficient and dependable response.

Proper installation and maintenance of an automatic transfer switch are crucial for its optimal performance and longevity. Although a qualified electrician should always perform installation, end-users can perform basic maintenance tasks, such as routine inspections, cleaning, and testing. Specialized servicing should be left to professionals to ensure the ATS remains in peak condition.

The main components of an automatic transfer switch include the transfer switch, a controller, and a power source. The transfer switch, either open transition or closed transition, connects and disconnects the load between the utility power and the standby generator. The controller monitors voltage levels and initiates the load transfer when required. Finally, the power source, typically a backup generator, supplies power during an outage.

An ATS is vital for ensuring an uninterrupted power supply during an outage. First, it detects a power outage and signals the standby generator to start. Once the generator runs, the ATS conducts a load transfer from the primary power source to the backup power system. After power is restored, the ATS switches the load back to the utility power and shuts down the generator. This smooth process minimizes the detrimental effects of power outages.

Critical facilities, such as hospitals and data centers, require a bypass isolation switch for added redundancy and maintenance flexibility. The bypass isolation switch enables the automatic transfer switch to be serviced or replaced without interrupting power to the facility.

Single-phase and three-phase are the two main types of automatic transfer switches, with their use varying based on application and load requirements. Single-phase switches are common in residential settings, while three-phase switches cater to commercial and industrial applications.

Safety should always be a top priority when working with an ATS. Please ensure that a licensed electrician installs the switch and follows the manufacturer's guidelines for maintenance and testing. In addition, appropriate personal protective equipment should be used when handling electrical switchgear, and all local and national electrical codes should be observed.