There is another fact that may be overlooked: There is no device, ground or method of grounding that can withstand a direct lightning strike. With a potential for a billion volts, the puny grounds and surge devices are incapable of containing a direct strike. Telephone equipment is exposed three ways. 1 through the electrical service, 2 through the telephone CO trunks and 3 via static through the telephone instrument cabeling. Many of the "fried" systems may be a victim of static electric which traveling through the telephone instrument wiring, in winter months, is extremely likely and can have potentials high enough to cause lightning like damage, but on a much smaller and less dramatic scale.
The bottom line here is make absolutely sure the telephone equipment is bonded and NOT the "best" ground in the facility. Take accurate readings and make sure the telephone equipment bonds are not mis-matched impedance wise from the good ground. If you are in a smaller facility, take the time and make sure there is a solid metallic ground with a bonding jumper across the water meter. In large, transformer fed facilities, make sure your telephone ground is the building main ground and not a high impedance electrical ground being derrived from a step down service transformer. The NEC and the NESC both require large buildings to maintain structural steel bonding. Don't be fooled. Take readings. Not only is this an equipment protection situation, it is also and, more importantly, a life safety issue.
Rcaman
Last edited by Rcaman; 03/20/14 11:47 AM.
