You want to know you’re receiving the best when it comes to the dependability of a power backup system for your residential or commercial needs. It’s important to remember that strength, size, and cost are not always indicators of excellence. An automatic transfer switch is valuable for the seamless transition of power from the main supply to the backup during an outage.

But what kind of automatic transfer switch does your application require? You might be shocked to learn that your ideal solution depends on several variables, including your application’s size, electrical requirements, and power source. But for now, let’s concentrate on how your ATS functions in your power box.

Automatic transfer switch in a nutshell

An automatic transfer switch (ATS) is a device that automatically alternates between two separate power sources. It is beneficial in situations where a backup power supply is required. The market offers a variety of automatic transfer switch equipment because switching requirements vary throughout applications. These mainly differ in the amperage or voltage rating and the number of poles.

However, connection or power transition techniques are typically used to categorize ATSs. Thus, the following are the varieties of automated transfer switches available depending on the power transition mode:

  • Make before break type (open transition)
  • Break before make type (closed transition)
  • Delayed transition type
  • Soft (gradual connection) switches
  • Bypassable switches

Here is a more detailed explanation of these types of automatic transfer switches.

Open transition automatic transfer switch

An open transition transfer switch has a break-before-make transition mechanism. During the power transfer, the switch will disconnect from the first power source before connecting to the second source.

Therefore, an open transition ATS typically results in a brief power loss. For most applications, this is usually okay and takes a few seconds. However, this kind of automatic transfer switch might not be the best option for mission-critical systems like hospital life support machines.

Open transition ATS equipment is usually utilized in modest applications, like home backup power systems. It’s also typical in scenarios—like those involving building lighting systems—where a brief blackout would not be alarming. These are the most popular and, because of their simplicity, are frequently quite dependable.

Closed transition automatic switch transfer

As a make-before-break device, a closed transition transfer switch is the opposite of an open transition automatic transfer switch (ATS). This implies that during the power transfer sequence, the switch will connect to the alternative source before cutting its connection to the current source.

Utilizing a closed transition ATS has the primary benefit of minimizing the brief power loss that occurs during transfer—roughly 100 milliseconds. Thanks to its closed transition approach, the switch allows for a smooth power return to the primary source.

Therefore, mission-critical applications where even a brief power outage could cause issues frequently use these kinds of automatic transfer switch mechanisms. The UPS systems used in communication centers, security, and healthcare facilities are examples of these applications.

Soft loading automatic transfer switch

This is a variation of the closed transition ATS. Rather than instantly connecting to the new power source, this kind of switch will gradually ramp up the connection. This prevents abrupt voltage or current variations that can harm electrical equipment.

Applications, where a sudden shift in load could cause issues, are where these kinds of automated transfer switch connections find value. For instance, data centers frequently employ soft-loading ATSs to prevent damaging delicate electronic equipment.

A delayed transition automatic transfer switch

A closed transition ATS and a delayed transition transfer switch are comparable. One of the primary distinctions is the timing of the power transfer or transition process, which is typically a few seconds (or even up to ten seconds) late. A break-before-make is still in place, but a deliberate and planned delay exists before the transition from grid to generator power (and vice versa). Heavy industrial equipment is susceptible to power surges by turning on and off quickly; therefore, this delay is fail-safe.

These kinds of automatic transfer switches are handy when powering a big electric motor (20 HP and up) or an inductive load. When unplugged from live power, these loads typically produce brief voltages, which may harm equipment or premature trip breakers. By delaying things, these voltages can drop to safe levels and avoid an inrush of current.

Bypass transfer switch

In technical terms, the bypass transfer switch is two parallel-connected transfer switches within the same assembly. The primary ATS acts as the main switch, disseminating the load to the emergency source and back again. Conversely, the bypass switch is utilized during regular ATS maintenance.

Typically, the bypass ATS is a manual switch; however, some switches have both switches on automatic mode. Typically, the primary ATS is installed in a draw-out carriage to facilitate removal without disconnecting the load. Bypass isolation transfer switches are frequently utilized in essential installations where the system needs to be switched on continuously to test or inspect the ATS. It enables technicians to isolate or circumvent the primary switch for maintenance purposes.

Open vs. Closed transition ATS: which is ideal for your needs?

A closed transition switch will smoothly transfer the power without any discernible interruption, whereas an open switch would momentarily disconnect the power before moving it to the other source. Consider your specific applications to choose the ideal ATS from that meets your needs.

If your application must avoid even the slightest power interruptions, the best choice is a closed transition switch. On the other hand, an open transition ATS switch might be a preferable option if your electrical system can withstand a minor power outage since it will cut the power for a short while before resuming the connection to the other source.

To sum up, your ideal type of automatic transfer switch will depend on your application’s unique requirements, so consider every electrical system component. Getting expert help will provide the expertise you need to select the best transfer switch for your unique requirements, saving you from having to deal with expensive blunders or annoying reinstallations.

Douglas Carl
the authorDouglas Carl