Section 240.87/Arc Energy Reduction
NEC 240.87 requires arc energy reduction methods on circuit breakers rated 1200 amperes or more to reduce the severity of arc flash events.
Where a circuit breaker is applied to switch or protect a circuit with a trip rating of 1200 amperes or more, one or more of the following arc energy reduction methods must be provided: (1) zone-selective interlocking, (2) differential relaying, (3) an energy-reducing maintenance switching with local status indicator, (4) an energy-reducing active arc flash mitigation system, or (5) an approved equivalent means. The documentation of the available fault current required by Section 110.24 is essential for selecting and validating the arc energy reduction method. This requirement applies to all installations, not just services, and covers both new and replacement circuit breakers.
Why this section exists
Large circuit breakers (1200A and above) protect feeders and services in commercial and industrial facilities where available fault currents are high. Without arc energy reduction, the incident energy during an arc flash event at this equipment can exceed the protective capability of standard PPE. The methods listed in 240.87 reduce clearing time or arc duration: zone-selective interlocking allows a downstream breaker to signal upstream breakers to delay tripping, differential relaying detects internal faults and trips in milliseconds, maintenance switches temporarily reduce trip settings, and active arc flash mitigation systems use light sensors to detect arcs and trip instantaneously.
What plan reviewers look for
Plan reviewers identify all circuit breakers rated 1200A or more on the one-line diagram and verify that an arc energy reduction method is specified for each. They check that the selected method is noted on the drawing or in the specifications. For zone-selective interlocking, they verify the communication wiring between breakers is shown. For energy-reducing maintenance switches, they verify the local status indicator is specified. They also verify that arc flash warning labels are required at each location.