Guys,
NFPA 70E Table 130.7(C)(15)(A)(b) provide arc flash PPE categories for various equipment. For motor control centers there are two entries
600-V class motor control centers (MCCs) - Parameters: Maximum of 65 kA short-circuit current available; maximum of 0.03 sec (2 cycles) fault clearing time; working distance 455 mm (18 in.) Arc flash PPE Category - 2, Arc flash boundary 5 feet
AND
600-V class motor control centers (MCCs) - Parameters: Maximum of 42 kA short-circuit current available; maximum of 0.33 sec (20 cycles) fault clearing time; working distance 455 mm (18 in.) Arc flash PPE Category - 4, Arc flash boundary 14 feet
So am I correct in assuming that the lower the short circuit current or the longer the clearing time, the more hazardous the situation?
Be gentle. I'm a chemical safety guy trying to figure electricity :happysad:
Thanks,
MikeCJ
NFPA 70E Table 130.7(C)(15)(A)(b) provide arc flash PPE categories for various equipment. For motor control centers there are two entries
600-V class motor control centers (MCCs) - Parameters: Maximum of 65 kA short-circuit current available; maximum of 0.03 sec (2 cycles) fault clearing time; working distance 455 mm (18 in.) Arc flash PPE Category - 2, Arc flash boundary 5 feet
AND
600-V class motor control centers (MCCs) - Parameters: Maximum of 42 kA short-circuit current available; maximum of 0.33 sec (20 cycles) fault clearing time; working distance 455 mm (18 in.) Arc flash PPE Category - 4, Arc flash boundary 14 feet
So am I correct in assuming that the lower the short circuit current or the longer the clearing time, the more hazardous the situation?
Be gentle. I'm a chemical safety guy trying to figure electricity :happysad:
Thanks,
MikeCJ