Adding Flexibility to Selective Coordination Designs

Selective coordination is a National Electrical Code (NEC) requirement 
for those systems that code defines as related to life safety. While the
 intent of selective coordination – restricting the potential impact of 
an electrical overload or short circuit – is easy to understand, putting
 such designs into practice isn’t always as simple. Mersen

Chuck Ross

Selective coordination is a National Electrical Code (NEC) requirement for those systems that code defines as related to life safety. While the intent of selective coordination – restricting the potential impact of an electrical overload or short circuit – is easy to understand, putting such designs into practice isn’t always as simple. Designing for selective coordination can require consulting engineers to carry out complicated coordination studies before specifying equipment, adding time and expense to related electrical projects.

The goal of selective coordination is to restrict the impact of an electrical fault to the closest upstream protective device, so a localized short circuit or overcurrent event doesn’t cascade into a system- or facility-wide outage. The NEC requires such protection, which often relies on fuse-based designs, for life-safety systems, because designing for coordination with breaker-based systems can be considerably more complicated. Fuses, however, can be problematic – not only can fuse panels take up more room than standard breaker boxes, but facilities also need to maintain an inventory of replacement fuses to address even the simplest overcurrent event.

An alternate option is a hybrid coordination panelboard that combines the size and operational advantages of circuit breakers with the protective capabilities of fuses. With these products, circuit breakers protect branch circuits and can simply be reset after common overload conditions. Fuses are used at the panel level to isolate more serious faults, and those fuses are sized to provide the necessary coordination with upstream devices. Additionally, at 20-in. wide, the panels require no more wall space than standard breaker boxes.


Photo courtesy of Mersen