In server rooms and data centers, the power must not drop even for a second. Making sure the supply switches automatically to a backup source on an outage is the job of an ATS. Let us explain what it is, how it works and when it is worth it.

What an ATS is

An ATS (Automatic Transfer Switch) is a device that automatically switches the power from the main source to a backup when the main one fails. It does this without human intervention and in a fraction of a second. Thanks to this, the connected devices do not even feel the power change.

How it works

An ATS continuously monitors the main electricity supply. When the voltage fails or drops below a safe level, it immediately switches to the backup source, which can be a second independent feed, a generator or another branch. When the main source recovers and stabilizes, the ATS switches the power back, also automatically.

Switching time and why it matters

A common ATS with an electromechanical switch needs on the order of tens to hundreds of milliseconds to switch over. Sensitive devices (servers, network gear) could reboot during such a pause. That is why an ATS is almost always combined with a UPS, which bridges that short gap from the battery so the devices do not even notice the outage.

ATS versus STS (static transfer switch)

An ATS and an STS solve a similar task but differ in technology and speed:

  • An ATS uses a mechanical switch, is cheaper and robust, but the switchover takes longer.
  • An STS (Static Transfer Switch) switches with semiconductors, with no moving parts, and manages it in single-digit milliseconds, so the load barely feels the change. It is more expensive and used where not even the shortest pause is acceptable.

ATS versus UPS versus generator

These three are often confused, yet each solves something different:

  • A UPS bridges a short outage from a battery, on the order of seconds to minutes, as we write in the article on a UPS and surge protection.
  • A generator supplies power long-term, but takes a moment to start up.
  • An ATS switches between sources.

In practice they work together: on an outage, the UPS bridges the few seconds until the ATS switches to the generator, which then powers the operation long-term. That creates uninterrupted power.

Types of ATS

  • A rack ATS switches two power sources for servers that have two power inputs. When one branch fails, the server keeps running from the other.
  • A large ATS switches the power of a whole building or server room between the grid and a generator.

When to deploy it

An ATS makes sense wherever you have two independent feeds or a generator and where the power must not drop: server rooms, important servers and operations running 24/7.

A practical tip: layered protection

The most reliable solution combines several layers: servers with two power supplies, an ATS, a UPS and a generator. Each layer covers a different situation, and together they ensure the operation runs even during an outage. The article how to choose a backup power source (UPS) helps you pick the right UPS.

Dealing with server room power or backup power for a company? Get in touch, we will design a reliable tailored solution as part of IT support for companies.

This article is part of our Cybersecurity overview.