The NEC Section 240.87 was added to provide for circumstances when a circuit breaker is used that had no instantaneous trip protection. This addition was introduced with the intent to reduce the clearing times of circuit breakers contained in large equipment where high arc flash levels are often present. The code allowed for three acceptable methods to mitigate risk:

• Zone selective interlocking
• Differential relaying
• Energy-reducing maintenance switching with a local-status indicator

Updates to the NEC Section 240.87 were expanded to include “Arc Energy Reduction.” The updated code addressed all circuit breakers that are rated or could be adjusted to 1200 A and above. Additional mitigation methods were added to the list of acceptable methods:

• Energy-reducing active arc flash mitigation system
• An approved equivalent means

The introduction of an “approved equivalent means” has let some manufacturers enter the market with reduction “solutions” that may not stand up to scrutiny. It’s important to work with a supplier that has a solid reputation for delivering reliable solutions. This mitigation method also puts additional responsibility on inspectors, who must be extremely precise and diligent when assessing facilities.

In 2017, arc energy reduction requirements were expanded to include fuse applications with the addition of Section 240.67. This section applies where fuses rated 1200 A or higher are installed. (The implementation of this section was effective January 1, 2020.)

Section 240.67 states that unless a fuse has a clearing time of 0.07 seconds or less, one of the following means shall be provided and set to operate at less than the available arcing current. Approved mitigation methods are:

• Differential relaying
• Energy-reducing maintenance switching with a local-status indicator
• Energy-reducing active arc flash mitigation system
• An approved equivalent means

The NEC Section 240.87 for circuit breaker applications included two more methods allowing for:

• An instantaneous trip setting that is less than the available arcing current
• An instantaneous override that is less than the available arcing current

An additional provision went into effect that mandates performance testing by a qualified individual. Applicable to both Sections 240.67 and 240.87, the code stipulates that “the arc energy reduction protection system shall be performance tested by primary current injection testing or another approved method when first installed on site.”

Section 240.67 included an additional method, allowing for the use of:

• Current-limiting electronically actuated fuses

Section 240.87 had a revision to the two methods most recently added to read:

• An instantaneous trip setting. Temporary adjustment of the instantaneous trip setting to achieve arc energy reduction shall not be permitted.
• An instantaneous override