UFC 3 -520-01
June 10, 2002
Ensure intercom circuit protection is listed to UL 497A and it should provide a
minimum surge current rating of 9,000 amperes. Protection should be provided on
points of entry and exit from separate buildings.
Fire alarm and security alarm system loops and addressable circuits that
enter or leave separate buildings should have a minimum of 9,000 amperes surge
current rating. Ensure the protection is listed to UL 497A for data communications and
UL 497B for annunciation.
Coaxial lines should be protected at points of entry and exit from separate
buildings. Single stage gas discharge protectors can be used for less critical circuits.
Multistage protectors utilizing a gas discharge protector with solid-state secondary
stages should be used to obtain lower let-through voltages for more critical equipment.