One major caveat to consider with the ARm though: Both inputs MUST ALWAYS be in phase. This usually is not the case, so these units are used more for manual UPS bypass switches. For an automatic transfer switch where both power sources can be potentially asynchronous, or out of phase, such as a UPS and a motor-generator, see the ATs Series.

Typical ARm applications
Designed for situations where reliability and predictability matter to the enterprise. 
Examples: telecommunications equipment, export markets, file servers, routers, digital copiers, office machines, industrial controllers (PLC), automatic test equipment (ATE), laboratory analyzers and other sensitive, specialized microprocessor-based equipment.

Key automatic redundancy module benefits
The ARm will provide uninterrupted ac to your load even in the event of UPS failure. ARms your critical equipment against extended power outages and catastrophic system shutdowns caused by accidental circuit breaker trips, UPS overload conditions, weak or old UPS batteries, routine and preventive maintenance of UPS, accidental UPS shut down, loose power cords, or UPS failure. ARm-1000 permits unlimited redundancy using any combination of independent (separate) ac circuits, UPS systems, generator-backed ac circuits, etc.

How the ARm automatic transfer switches work
The ARm is fed by two ac power sources. When the primary power source detector circuit senses a loss of power on that circuit, a relay immediately switches the load over to the backup power source feed in less than 10 ms. This is fast enough to be invisible to computer switch-mode power supplies.