UL 497E OUTLINE

Description / Abstract: This Outline of Investigation covers protectors for antenna lead-in conductors. These devices are used to limit surges on the cable that connects the antenna to the receiver/transmitter electronics and are connected between the conductors and the grounded shield or other ground connection. Typical applications include antenna installations for radio and television receiving equipment, amateur radio transmitting and receiving equipment, cellular telephone towers and WiMax or WiFi wireless networks.

As covered by these requirements, protectors for antenna lead-in conductors typically consists of air gap arresters, gas tube arresters, solid-state arresters or quarter-wave stub type devices, or combinations of these devices. Other technologies are not excluded. They may or may not contain additional components such as inductors or blocking capacitors. These protectors are intended to protect equipment, wiring, and personnel at the premises against the effects of excessive potentials and currents on the conductors caused by lightning.

These devices operate to divert a surge current to earth, and control the residual voltage (also known as let-through voltage) to a suitable level. Once the surge current has subsided, the device automatically returns normal operation and reset to a state ready to receive the next surge. Residual voltage limits or their suitability to minimize damage to connected equipment is not within the scope of these requirements.

These protectors are investigated for their maximum discharge current (I_max) capability using an 8/20 current waveform. This is the maximum impulse current the protector can withstand, including after environmental conditioning, without affecting its surge limiting capability or creating a risk of fire, fragmentation or electrical shock.

This Outline does not cover the following:

a) Lightning protective devices for the protection of secondary distribution wiring systems and equipment.

b) Antenna discharge units for radio and television receiving appliances that are covered by the Standard for Antenna-Discharge Units, UL 452.

c) Lightning conductor and air terminals for connection of lightning rods for building protection.

d) Protectors for fire alarm signaling circuits that are covered by the Standard for Protectors for Data Communications and Fire-Alarm Circuits, UL 497B.

e) Equipment covered by the Standard for Secondary Protectors for Communications Circuits, UL 497A.

f) Equipment covered by the Standard for Surge Protective Devices, UL 1449.

g) Equipment covered by the Standard for Protectors for Paired-Conductor Communications Circuits, UL 497.

h) Equipment covered by the Standard for Protectors for Coaxial Communications Circuits, UL 497C.

i) DC blocking connectors or components that do not have lightning protection as their primary function.

j) Applications where follow-on currents may occur, such as installations where communications wiring is routed on shared facilities with electrical distribution systems.

Special installation methods are required for equipment connected to wire-line communication facilities serving high-voltage electric power stations operating at greater than 1 kV. These requirements do not cover the equipment or devices used in the design of such installations. Special system design requirements, such as those covered by Recommended Practice for the Protection of Wire-Line Communication Facilities Serving Electric Power Locations, IEEE 487, shall be followed to reduce the risks associated with wire-line communication facilities serving such power stations.