In this thread: http://electrical-contractor.net/ubb/Forum1/HTML/007133.html
my reply to one post brought up a point I feel is worth discussing.
Today's power demands are much greater than they were say, 30 or 50 years ago. This of course required the POCO's to upgrade distribution equipment and feeders to accomodate the growing load. Yet in both industrial and commercial locations, some very old but still servicable switchgear and breaker panels are in use.
The concern I have is that said older gear was designed or spec'd for a much lower short circuit interrupting ability than that which could now available to it.
What are some of the potential consequences of this? I see:
1 - Failure of breakers, fuse assemblies and disonnect switches under a Phase-Gnd/Neut. or Phase-Phase fault, with the failure mode most likely violent;
2 - Mechanical failure of buss and enclosures from the forces generated by #1;
3 - Another consequence is failure to clear a circuit as designed, resulting in additional damge and/or;
4 - Severe risk of damage to property or injury or death to persons; and
5 - Risk of extended outages or downtime while the system is repaired.
NEC makes no mention of this situation, and frankly, it would be impossible to require/enforce the changeout of equipment that is no longer able to withstand greater available short circuit current.
But has there ever been, or should there be, a requirement for a complete "power" survey including ASSC and new load factors when major switchgear is being overhauled/ replaced?
I look forward to hearing from everyone here on this subject....