Understanding Automatic Transfer Switches (ATS)
Choosing the right automatic transfer switch (ATS) is crucial for ensuring a seamless transition between power sources during an outage. Different ATS types cater to various applications, each with its advantages and limitations. In this guide, we’ll explore the four most common types of ATS and their ideal use cases.
How Do Automatic Transfer Switches Work?
A transfer switch operates in three primary steps:
- Power Failure – The normal utility power source fails.
- Power Transfer – The ATS shifts the load to the backup power source (generator or secondary utility feed) once the backup power is stable and within the correct voltage and frequency limits. This transfer can be automatic or manual, but this article focuses on self-acting (automatic) switches.
- Power Restoration – When the utility power is restored, the ATS shifts the load back to the normal power source.
Types of Automatic Transfer Switches
1. Break-Before-Make (Open Transition) ATS
Best for: Applications where a brief power interruption (up to two seconds) does not impact business operations or safety.
- This switch disconnects from the utility power source before establishing a connection with the generator.
- Results in a momentary power loss during transfer.
- Commonly used in businesses or facilities where a short power loss is acceptable.
2. Make-Before-Break (Closed Transition) ATS
Best for: Critical applications requiring uninterrupted power, such as hospitals, data centers, and large commercial facilities.
- Maintains a connection with both power sources for a fraction of a second (typically around 0.1 seconds).
- Eliminates power interruptions during the switch.
- Ensures smooth transitions without backfeeding or power instability.
- Essential for operations where even momentary downtime could lead to significant disruptions or safety risks.
3. Delayed Transition (Center Off) ATS
Best for: Industrial applications with heavy inductive loads that generate high inrush currents.
- Introduces a purposeful delay before switching between power sources.
- Prevents power surges that can occur when high-power machinery is powered on or off.
- Provides an added layer of safety for heavy industrial equipment.
4. Solid-State ATS
Best for: Highly sensitive applications requiring ultra-fast switching, such as light dimming, motor speed control, and precision electronics.
- Uses transistor technology for rapid, sub-cycle transfers.
- No moving parts, ensuring durability and minimal maintenance.
- Although there is technically a break in load current, the transfer speed (typically 5 milliseconds) prevents voltage dips or interruptions.
- Ideal for applications where power fluctuations could damage sensitive equipment.
Choosing the Right ATS for Your Needs
Selecting the correct ATS depends on factors such as the critical nature of your operations, the type of load your facility handles, and your tolerance for brief power interruptions. For mission-critical applications, a Closed Transition or Solid-State ATS is ideal. For industrial environments, a Delayed Transition ATS offers protection against power surges. If a momentary power loss is acceptable, an Open Transition ATS provides a cost-effective solution.
Investing in the right ATS ensures seamless power transitions, minimizes downtime, and enhances operational reliability. If you’re unsure which ATS suits your needs, consult with a professional to assess your facility’s power requirements.
