Arc energy reduction for fuses of 1,200 A and up
Where fuses rated 1,200 A or more are installed, the fuse must clear within 0.07 second at the available arcing current, or one of the energy-reducing methods the code lists must be provided, with documentation and on-site testing.
What the code requires
240.67 applies wherever fuses rated 1,200 A or higher are installed.
The fuse must clear in 0.07 second or less at the available arcing current. If it does not, one of these must be provided and set below the arcing current: differential relaying, energy-reducing maintenance switching with a local status indicator, an energy-reducing active arc-flash mitigation system, current-limiting electronically actuated fuses, or an approved equivalent means.
Documentation must show where the fuses are and that the chosen method is set below the available arcing current. It must be available to those authorized to design, install, operate or inspect the installation. The method must be performance tested when first installed on site, 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
- Large switchboard fuses installed with no arc-energy documentation or test record are a common holdup at final inspection.
- The documentation must show the fuse locations and that the method is set below the available arcing current, and it must be available to your inspector.
Related sections
- NEC 110.16: Arc-flash warning labels on commercial equipment
- NEC 230.71: How many service disconnects are allowed
- NEC 240.87: Arc energy reduction for breakers 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