GAI-Tronics 265-001 Intrinsically-Safe Telephone Rack-Mount System - Manual (Page 8)

Pub. 42004-200B
Intrinsically Safe Rack-Mount Telephone System Page: 8 of 13
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02/06
Lightning Protection
Telephone lines are susceptible to lightning strikes and must be properly protected and maintained. On-
premise line protection is usually provided at the building entrance by the responsible telephone company
when it is installed. This protection is often neglected after installation.
Degradation of conventional protection, such as carbon blocks or gas discharge types, will occur with
each lightning strike. To ensure safe operation, protective elements should be replaced frequently and
checked for proper connection and grounding. Gas discharge types are by far the most robust, cost-
effective means of protection.
The registered I.S. equipment meets all isolation and safety requirements of FCC, Part 68 and UL 913.
However, lightning strikes are not predictable or considered to be a condition of fault likely to occur in
practice as defined by the guidelines for intrinsic safety. Therefore, it is imperative that the user employ
and maintain a proper lightning protection scheme. This is true for all hazardous area equipment and all
telecommunications equipment subject to lightning.
Figure 3. Example of Lightning Protection Design
Proper grounding is the most critical consideration in any intrinsically-safe system. Unsafe energy levels
are limited by the protective diode barrier with reference to the I.S. ground terminals.
It is imperative to make good mechanical and electrical ground connections to maintain intrinsic safety
(for low impedance ground connections, less than 1 ohm required; less than 0.1 ohms is recommended).
Use the latest National Electrical Code (NEC) published by NFPA to ensure that proper ground
connections are made.
References: UL 913 NEC, Article 504
N OTE : Do not connect the intrinsically-safe ground directly to the ac power ground terminals.
WARNING
Installation must be in accordance with GAI-Tronics Pub. 42004-380 to ensure intrinsic safety.