Arc energy reduction for breakers of 1,200 A and up
Where a breaker's highest continuous trip setting is 1,200 A or more, the code requires one of seven arc energy reduction methods set below the available arcing current, with documentation and testing when first installed.
What the code requires
240.87 applies where a circuit breaker's highest continuous trip setting, whether its rating or the highest it can be adjusted to, is 1,200 A or more.
One of seven methods must be provided and set below the available arcing current: zone-selective interlocking; differential relaying; energy-reducing maintenance switching with a local status indicator; an energy-reducing active arc-flash mitigation system; an instantaneous trip setting below the arcing current; an instantaneous override below the arcing current; or an approved equivalent means. Temporarily adjusting the instantaneous trip setting does not count.
Documentation must show the breaker locations and that the method is set below the available arcing current, and be available to authorized persons. The method must be performance tested on site when first installed, by qualified persons following the manufacturer's instructions, using primary current injection or another approved method. A written record of the test must be available to your inspector.
On the job
- A 1,200 A main breaker installed with no arc-energy method, documentation or test record is a common correction.
- Using two to six smaller service disconnects (230.71) can keep each device under 1,200 A.
Related sections
- NEC 110.16: Arc-flash warning labels on commercial equipment
- NEC 230.71: How many service disconnects are allowed
- NEC 230.95: Ground-fault protection on large commercial services
- NEC 240.6: Standard breaker and fuse sizes
- NEC 240.67: Arc energy reduction for fuses of 1,200 A and up
Where this comes from
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Kyle Robert Anderson KBC Electric · CSLB #1073066 · C-10 Electrical · Licensed since 2021