Jim Degnan, P.E., Principal, Sparling, Seattle

A Critical Look at Selective Coordination

The new requirements for selective coordination of emergency and legally required standby systems in Sections 700.18 and 701.27 of the 2005 National Electrical Code (NEC) are challenging electrical engineers to intensively consider how systems respond to short circuits. Meeting this challenge raises questions regarding the code requirements, how other aspects of system design are compromised and what constitutes compliance. While the probability of owners benefiting from selectively coordinated electrical systems is small, the likelihood of incurring significant costs to ensure selective coordination is a certainty with the 2005 NEC. As electrical engineers consider the impact of selective coordination, there is a growing consensus that this is the wrong direction for the NEC, and that this area of design should be returned to engineering judgment. In fact, there were more than a dozen proposed changes to the 2008 NEC to delete these new requirements or better define them. Unfortunately, the just-released NEC Report on Proposals showed that there were not enough Code Panel votes to return this design area to engineering judgment.