Surge protection for telecommunications and fire-alarm circuits, US and Canadian markets; Part B - data-transmission and fire-alarm circuits.
UL 497B covers protectors for data-transmission and fire-alarm circuits: single- and multipair spark-gap, gas-discharge and solid-state arresters, with or without fuses, protecting equipment, wiring and personnel against excessive voltages and currents of atmospheric origin.
The standard excludes protection of primary distribution systems, antenna discharge units, building lightning-protection systems and telephone-line protectors (which are covered by UL 497 / UL 497A).
A signal-line protector listed to UL 497B is approved for use in fire-alarm and data circuits in the US/Canadian market, which is relevant when exporting railway signalling or lineside telecommunications equipment.
