0.1 sec in Ddenver
0.1 sec in Ddenver
Here in Denver, we are not requiring the OCPDs to be selectively coordinated down to 0.01 seconds. You only need to coordinate down to 0.1 seconds.
To be honest, 0.01 seconds is very difficult to achieve without going to almost all fuses, and it doesn?t absolutely guarantee total coordination. The NEC doesn?t provide us with a specific level of selective coordination. NFPA 99 states that selective coordination of the essential electrical systems shall selectively coordinate for the period of time that a fault?s duration extends beyond 0.1 seconds. I think that healthcare facilities are the most restrictive and critical case for OCPD coordination, to prevent loss of life during life-saving procedures such as operations. Although NFPA 99 is not an adopted code by the city of Denver's Building Department (that?s us), it is still used as a guideline. If the most critical type of healthcare facility is only required to be coordinated down to 0.1 seconds per NFPA 99, then I think that it is reasonable to apply an OCPD coordination down to only 0.1 seconds for commercial buildings. Also, full coordination could compromise safety and system reliability, resulting from large current inrushes that are due to instantaneous reestablishment of connections to heavy loads.
