UL 1008A

These requirements in UL 1008A cover automatic, non-automatic, and manual transfer switches, operating at above 750 V AC, and intended for use in ordinary locations to provide for power as follows:

• Automatic transfer switches for use in emergency systems in accordance with Articles 517-Health Care Facilities, 700-Emergency Systems, 701-Legally Required Standby Systems, and 702-Optional Standby Systems of the National Electrical Code, ANSI/NFPA 70; and the Standard for Health Care Facilities, ANSI/NFPA 99.
• Transfer switches for use in optional standby systems in accordance with Article 702 of the National Electrical Code, ANSI/NFPA 70.
• In legally required standby systems in accordance with Article 701 of the National Electrical Code, ANSI/NFPA 70.
• Automatic transfer switches for use in accordance with the National Fire Protection Association Standard for Centrifugal Fire Pumps, ANSI/NFPA 20.
• Non-Automatic transfer switches for use in accordance with Articles 517-Health Care Facilities, and 702-Optional Standby Systems of the National Electrical Code, ANSI/NFPA 70; and the Standard for Health Care Facilities, ANSI/NFPA 99.

An automatic transfer switch for use in a legally required stand-by system shall comply with the requirements for a transfer switch for emergency systems.

These requirements cover transfer switches rated greater than 750 Volts, up to 46 kV.

These requirements cover transfer switches together with their associated control devices including, but not limited to, voltage sensing relays, frequency sensing relays, and time delay relays.

An automatic transfer switch as covered by these requirements is a device that automatically transfers a common load from a normal supply to an alternate supply in the event of failure of the normal supply, and automatically returns the load to the normal supply when the normal supply is restored. An automatic transfer switch may be provided with a logic control circuit that inhibits automatic operation of the device from either a normal to an alternate supply, or from an alternate to a normal supply when the switch reverts to automatic operation upon loss of power to the load.

A non-automatic transfer switch as covered by these requirements is a device, operated manually by a physical action, or electrically by a remote control, for transferring a common load between a normal and alternate supply.

A transfer switch may incorporate overcurrent protection for the main power circuits.

These requirements only cover completely enclosed transfer switches.

Transfer switches are rated in amperes and are considered to be acceptable for total system transfer, which includes control of motors, electric-heating loads, and transformer loads.