Being Selective When Talking About Coordination

Ensuring a minor branch-circuit electrical fault doesn’t travel any 
farther upstream is a goal of any electrical designer’s plans. However, 
in some settings, isolating such problems is especially critical. This 
is why the National Electrical Code (NEC) has paid a great deal of 
attention to the specification of appropriate fuses and/or circuit 
breakers to achieve “selective coordination” over the years. Eaton Bussmann

Ensuring a minor branch-circuit electrical fault doesn’t travel any farther upstream is a goal of any electrical designer’s plans. However, in some settings, isolating such problems is especially critical. This is why the National Electrical Code (NEC) has paid a great deal of attention to the specification of appropriate fuses and/or circuit breakers to achieve “selective coordination” over the years.

Unfortunately, the NEC’s requirements haven’t always been easy to understand – in fact, few topics in electrical-system design are as confusing as selective coordination. In large part, this is because the actual language used to describe those requirements in trade magazines and other commentary has sometimes been less than specific. To ease this confusion, the 2014 edition of the National Electrical Code (NEC) has called out specific provisions that help define “coordination” and “selective coordination.”

Perhaps because it has seemed awkward to always include the words “selective” or “selectively” in every reference to selective coordination, it’s often been dropped. Over time, this has led to a belief among some that the terms mean the same thing, and it made it difficult for design engineers to understand exactly where specific levels of overcurrent performance were expected. The 2016 NEC has cleared this up by specifying that:

  • Selective coordination applies for the full range of overcurrents on the system and the full range of overcurrent device interrupting times associated with those overcurrents.
  • Coordination applies to circuit protection devices for any fault time extending beyond 0.1 seconds.
So, in other words, selective coordination is a stricter approach than coordination, on its own. Keeping this distinction clear, moving forward, will make every electrical designer’s job a little easier.


Photo courtesy of Eaton Bussmann