240.87 Arc Energy Reduction.
Code Change Summary: Revisions were made to clarify the intent and permitted methods of arc-energy reduction.
The idea behind arc-energy reduction is to temporarily place the energized electrical equipment in a state where there will be less arc-energy (from a possible fault condition) in the event that an accident occurs while the servicing electrician is working in the energized gear.
Certain conditions may warrant the need to perform work on energized electrical equipment. Arc-energy reduction is a way to reduce the amount of potential arc-energy that may occur while a worker is servicing energized equipment.
Often, large frame circuit breakers are equipped with an instantaneous trip adjustment. Workers performing maintenance on live electrical equipment downstream of this breaker might adjust the instantaneous trip sensitivity in hopes that the breaker will trip faster during a fault, thus reducing the arc energy since the faster the breaker eliminates the fault condition, the less exposure a worker has to the arc energy. A temporary adjustment during servicing is not the intent of 240.87.
Prior code language could be interpreted to apply to any size circuit breaker. This was not the original intent when this section first appeared in the 2011 NEC®.
New code language makes it clear that the code section applies to larger frame circuit breakers only. Also, two new arc-energy reduction methods have been added as well as a new informational note clarifying the purpose of an energy-reducing active arc flash mitigation system.
Below is a preview of the NEC®. See the actual NEC® text at NFPA.ORG for the complete code section. Once there, click on the “free access” tab and select the applicable year of NFPA 70 (National Electrical code).
2011 Code Language:
240.87 Noninstantaneous Trip. Where a circuit breaker is used without an instantaneous trip, documentation shall be available to those authorized to design, install, operate, or inspect the installation as to the location of the circuit breaker(s). Where a circuit breaker is utilized without an instantaneous trip, one of the following or approved equivalent means shall be provided:
(1) Zone-selective interlocking
(2) Differential relaying
(3) Energy-reducing maintenance switching with local status indicator
2014 Code Language:
240.87 Arc Energy Reduction. Where the highest continuous current trip setting for which the actual overcurrent device installed in a circuit breaker is rated or can be adjusted is 1200 A or higher, 240.87(A) and (B) shall apply.
(A) Documentation. Documentation shall be available to those authorized to design, install, operate, or inspect the installation as to the location of the circuit breaker(s).
(B) Method to Reduce Clearing Time. One of the following or approved equivalent means shall be provided:
(1) Zone-selective interlocking
(2) Differential relaying
(3) Energy-reducing maintenance switching with local status indicator
(4) Energy-reducing active arc flash mitigation system
(5) An approved equivalent means
