Static and Transfer Switches

UPS Static Transfer Switches including Bypass style

Uninterruptible Power System Switchgear — Static, Transfer & Bypass Switches

Keep critical loads online during faults, maintenance, or source changes. This category covers three closely related
switch types used with UPS systems: static transfer switches (STS) for sub-cycle electronic transfers between sources,
automatic transfer switches (ATS) for utility↔generator or source selection using mechanical power contacts, and
bypass switches (electronic and manual) that route power around the UPS for protection or service.

Whether integrated inside a double-conversion UPS or installed externally as stand-alone gear, these devices preserve uptime,
maintain selective coordination, and provide safe pathways for planned service without dropping the load.

At-a-Glance Comparison

*Representative ranges; consult the specific datasheet for exact performance and coordination requirements.

When to Use Which

• STS: Your load is dual-corded or on a PD/STS, and you need seamless A/B source selection with sub-cycle transfers.
• ATS: You’re selecting between utility and generator (or two utilities) at the service or distribution level.
• Static Bypass (UPS internal): You want the UPS to ride through inverter faults/overloads by momentarily using bypass power.
• Maintenance Bypass: You need a safe, interlocked path to remove a UPS from service without dropping the critical bus.

Common Topologies

• Utility → UPS (with internal static bypass) → Critical Bus — standard double-conversion path.
• Dual Source A/B → STS → Critical Bus — seamless A/B selection for mission-critical loads.
• Wrap-Around Maintenance Bypass — interlocked breaker scheme that isolates the UPS for service while the load remains energized.