240.67 Arc Energy Reduction.
Code Change Summary: Revised code language on Arc energy reduction for fuses.
Placing electrical equipment into a safe working condition (de-energizing) is by far the best way to avoid electrical related injuries but there are instances where hot work is permitted.
The movement to reduce arc energy and protect workers servicing energized equipment is on. The 2014 NEC® began raising awareness by the changes made in 240.87 pertaining to large frame circuit breakers. The 2017 NEC® continued by introducing language that provided similar rules for large fuses.
Arc energy occurs during an arc-flash event with energized equipment. Often, equipment is serviced or maintained while energized and the worker follows guidelines in NFPA 70E for proper work practices and ratings of required PPE in order to provide a level of safety while working on the live equipment.
The amount of potential arc energy is based on several factors, one of which is the fault duration or time the fault persists before an overcurrent device ahead of the faulted circuit opens to clear the fault condition. This code section was put in place to ensure an extra measure of safety for the worker. Using one of the permitted methods to reduce potential arc energy ensures additional worker safety should a mishap occur triggering an arc flash event.
In the 2020 NEC®, current-limiting, electronically actuated fuses were added to the list of methods permitted to reduce clearing time. New documentation requirements were also added to demonstrate that whatever method chosen to reduce clearing time is set to operate at a value below the available arcing current.
Finally, a performance test is now required for the arc energy reduction protection system when first installed on site. It’s one thing to install the arc energy reduction system but it’s another thing altogether to test it and verify that it functions as intended.
Below is a preview of the NEC®. See the actual NEC® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2020 NEC® edition of NFPA 70.
2017 Code Language:
240.67 Arc Energy Reduction. Where fuses rated 1200 A or higher are installed, 240.67(A) and (B) shall apply. This requirement shall become effective January 1, 2020.
(A) Documentation. Documentation shall be available to those authorized to design, install, operate, or inspect the installation as to the location of the fuses.
(B) Method to Reduce Clearing Time. A fuse shall have a clearing time of 0.07 seconds or less at the available arcing current, or one of the following shall be provided:
(1) Differential relaying
(2) Energy-reducing maintenance switching with local status indicator
(3) Energy-reducing active arc flash mitigation system
(4) An approved equivalent means
2020 Code Language:
240.67 Arc Energy Reduction. Where fuses rated 1200 A or higher are installed, 240.67(A) and (B) shall apply. This requirement shall become effective January 1, 2020.
(A) Documentation. Documentation shall be available to those authorized to design, install, operate, or inspect the installation as to the location of the fuses.
Documentation shall also be provided to demonstrate that the method chosen to reduce clearing time is set to operate at a value below the available arcing current.
(B) Method to Reduce Clearing Time. A fuse shall have a clearing time of 0.07 seconds or less at the available arcing current, or one of the following means shall be provided and shall be set to operate at less than the available arcing current:
(1) Differential relaying
(2) Energy-reducing maintenance switching with local status indicator
(3) Energy-reducing active arc-flash mitigation system
(4) Current-limiting, electronically actuated fuses
(5) An approved equivalent means
N 240.67(C) Performance Testing. The below code section may not match the printed book text but includes the current text that aligns with TIA 20-4 issued 8/6/2019.
The arc energy reduction protection system shall be performance tested by primary current injection testing or another approved method when first installed on site. This testing shall be conducted by a qualified person(s) in accordance with the manufacturer’s instructions.
A written record of this testing shall be made and shall be available to the authority having jurisdiction.
Informational Note: Some energy reduction protection systems cannot be tested using a test process of primary current injection due to either the protection method being damaged such as with the use of fuse technology or because current is not the primary method of arc detection.