Selective Coordination versus Arc Flash - the great debate and update

This paper will briefly cover Selective Coordination requirements as required in the National Electrical Code. Then protective device operation and selection with regard to code mandated full fault current range Selective Coordination will be discussed. Various aspects of Arc Flash Energy will be outlined. The concern of increased Arc Flash energy when code mandated Selective Coordination over the entire calculated available fault current range including a maximum 3 phase bolted fault will be covered. Included will be a discussion of why emergency systems, legally required standby systems and health care essential systems there were no real world problems associated with the previous partial fault current range selective coordination. The following two alternative proposals to modify full fault current range selective coordination for 600 volt and below equipment will be covered: 1) limiting selective coordination to 0.1 seconds and above, or 2) Full selective coordination except for the following cases: a) where arc flash energy levels at main ANSI C37 switchgear exceeds 40 cal/cm2 and b) where for other low voltage distribution and control equipment, other than ANSI C37 switchgear, arc flash energy levels exceeds 8 cal /cm2. In addition, new circuit breaker and equipment designs and options available to achieve both Selective Coordination as well as reduced Arc Flash energy will be reviewed. An update of some of the other alternatives that governmental bodies have taken regarding the adoption of the 2005 or 2008 NEC with modification of selective coordination requirements will be summarized.