The legally required standby system at your facility kicks in a few times each year. Twice over the past 12 months, it’s had two incidents. First, a feeder breaker tripped for no apparent reason; subsequent investigation revealed a branch circuit problem coincident to this. The second incident was similar, but on a different feeder breaker.
The plant manager rejects the idea there’s a selective coordination problem, because “Bob” set all the breakers and he has over 25 years of experience as an electrician. He says the feeder breakers are bad and should be replaced.
How should you attack this problem?
It’s true that “Bob” has extensive experience. And he’s probably a fine electrician. But that doesn’t mean he’s qualified to conduct a selective coordination study. Because so many breaker characteristics may be involved, developing a breaker coordination plan can be a complex undertaking.
The NEC recognizes this complexity. Thus, for a legally required standby system, the selective coordination study must be performed by a licensed professional engineer or other qualified person [701.27].
Hire an engineering firm to conduct this study. To solve this “mystery,” compare the existing installation to the study results.
