UL 1008S:2018 PDF Download

The UL 1008S:2018 standard provides specifications and requirements for solid-state automatic transfer switches used for lighting and power in optional standby systems. The standard specifies that these switches are not suitable for use as service entrance equipment, unless specifically marked as such. The standard applies to transfer switch equipment rated at 6000 A or less and 600 V or less.

The standard covers the complete transfer switch system, including associated control devices such as voltage sensing relays, frequency sensing relays, and time delay relays. It defines an automatic transfer switch as a device that automatically transfers a common load from a normal supply to an alternate supply in the event of a failure, and then returns the load to the normal supply when power is restored. It also allows for the inclusion of a logic control circuit that inhibits automatic operation in certain situations.

In addition, the standard covers non-automatic transfer switches that are manually operated or controlled remotely to transfer a common load between a normal and alternate supply. It specifies that a transfer switch may incorporate overcurrent protection for the main power circuits. The standard also addresses the different types of enclosures for transfer switches, including completely enclosed and open types intended for mounting in other equipment.

Furthermore, the UL 1008S:2018 standard states that transfer switches are rated in amperes and are generally suitable for controlling various types of loads, including motors, electric-discharge lamps, electric-heating loads, and tungsten-filament lamp loads. However, if a transfer switch is intended for controlling tungsten-filament lamp loads exceeding 30% of its ampere rating, it should be specifically marked and investigated accordingly. Additionally, a transfer switch may be limited for use with specific types of loads if it has been investigated and marked accordingly.