Some emergency power installations require multiple automatic transfer switches, each feeding a specific load. In many installations where noncritical loads are being served, specifications may call for manual or non-automatic transfer switches. This method is used because operating personnel are present and the loads are not of a critical nature requiring unattended automatic operation.
Because of the less critical function of this equipment, no specific industry requirements have been established. As a result, devices such as double throw disconnect switches have been used. Since the non-automatic transfer switches are part of the emergency power supply system, they should have the same UL 1008 electrical ratings as the automatic transfer switches feeding the more critical loads. In the event of a short circuit, the non-automatic transfer switches must have the same withstand current ratings as the automatic transfer switches and they must be as rugged and dependable.