Static Transfer Switches (STS) for Dual-Source Redundancy

A static transfer switch uses solid-state power electronics to transfer a critical load between two independent power sources almost instantly, typically within a fraction of an electrical cycle. This sub-cycle transfer is fast enough that downstream equipment continues without interruption, adding redundancy to power distribution beyond what a UPS or generator provides on its own.

An ATS uses mechanical contactors and transfers in a fraction of a second to a few seconds, suitable for utility-to-generator switching. An STS uses solid-state electronics for sub-cycle transfer, fast enough that sensitive loads see no interruption. STS units are used for critical distribution and dual-source paths where even a brief break is unacceptable.

STS units are used in critical power distribution to give downstream equipment or dual-corded loads two independent source paths with seamless transfer. They are common in data centers feeding PDUs or branch distribution from two UPS systems or buses, ensuring the load survives the loss of one source without interruption.

Sizing is based on the downstream load current, the voltage of your distribution, and redundancy requirements, with appropriate headroom. The STS must handle the full load on either source. Comp-Utility calculates the load and specifies the STS rating and configuration to integrate cleanly into your distribution and redundancy scheme.

Yes. An STS transfers between two existing sources but does not store energy, so it does not bridge an outage where both sources fail. UPS systems provide the ride-through energy, while the STS adds source redundancy. They are complementary: a typical design uses redundant UPS feeds with an STS for seamless source selection.

STS units require periodic inspection, controls and firmware checks, connection torque verification, infrared scanning, and testing of the transfer function to confirm sub-cycle operation. Because they protect critical distribution, verifying transfer behavior is important. Comp-Utility maintains and tests STS units as part of a power-system maintenance program.

As a distribution partner of Schneider Electric and Vertiv, Comp-Utility provides static transfer switches including the Schneider Galaxy STS and Vertiv Liebert STS2, among others, and services them vendor-agnostically. We specify, install, and maintain the right STS for your distribution. Call (512) 346-0999 to discuss your application.

Comp-Utility specs, installs, commissions, and maintains static transfer switches across Central Texas, including integration with UPS and distribution and 24/7 emergency response. Engineer-owned since 1992. Call (512) 346-0999 or email sales@comp-utility.com.