NFPA 70E 130.6(M) states:
After a circuit is de-energized by the automatic operation of a circuit protective device, the circuit shall not be manually re-energized until it has been determined that the equipment and circuit can be safely energized.
29 CFR 1910.334(b)(2) states:
After a circuit is deenergized by a circuit protective device, the circuit may not be manually reenergized until it has been determined that the equipment and circuit can be safely energized.
My first thought would be, "If the breaker is rated for the available short circuit current, I should be able to close it into a short-circuit without a problem." However, I've heard of cases where it seems that an appropriately-rated molded-case breaker was closed into a short-circuit, which resulted in an arc starting inside the breaker, leading to arc flash injuries.
What is the mechanism of such a malfunction? Age and abuse are possible contributing factors. Is there more to it? Is there some aspect of the construction of a molded-case circuit breaker that can result in an arc flash when closed into a short circuit, even if it was a brand new breaker of appropriate rating?
Best Answer
Depending on the supply, the prospective short circuit current could well be in the kilo-amps range, even if the breaker is only rated for tens of amps.
In such extreme cases, the breaker is simply required to break the current. It may not survive the damage. While it is breaking such a large current, there may be a substantial flash.
I wouldn't want to be the person holding the lever of a circuit breaker while it's in the process of breaking a 10kA fault.