What Does An Automatic Transfer Switch (ATS) Do In A UPS System?

Automatic Transfer Switches (ATS) are typically used to provide resilience for smaller uninterruptible power supplies (below 10 kVA) that can’t operate in a parallel configuration.

The ATS has two AC input power sources (‘A’ and ‘B’) and if/when one of these fails, the loads are automatically and instantaneously transferred to the other.

Automatic Transfer Switches like Riello UPS's Multi Switch ATS can also be used instead of a Power Distribution Units (PDU) for plug and play loads. In addition, ATSs protect against short circuits and offer the ability to switch output power connections on and off remotely over a network.

The ‘A’ and ‘B’ power sources feeding an Automatic Transfer Switch can be configured in a variety of combinations:

• ‘A’ supplied from the output of the UPS and ‘B’ from the mains supply
• Both ‘A’ and ‘B’ supplied from two separate UPS outputs
• Both ‘A’ and ‘B’ supplied from two separate mains supplies.

The above example highlights an ATS with two input supplies and up to eight outputs.

Further Reading:

• Multi Switch ATS
• Power Transfer Systems - Switches and Bypasses
• What does a Bypass Switch do in a UPS system?
• What does a UPS Group Synchroniser do?
• What does a UPS Parallel System Joiner do?
• Why use an external bypass with a UPS system?