1) Installation documentation
Documentation requirements changed slightly. A new requirement now mandates proof that installations have arc reduction technologies operating based upon arcing fault current. As always, documentation must be made available to those authorized to design, install, operate or inspect an installation as to the location of all OCPDs impacted. It’s critical to understand when these requirements apply and to realize that organizations can always exceed minimum Code requirements by approaching every design with an eye on arc flash hazards.
2) Safety methodologies
Installers, designers and authorities having jurisdiction must understand the entry point of requiring arc reduction technologies as part of 240.67 and 240.87. Circuit breaker requirements of 240.87 establish an arc reduction technology entry point based on circuit breaker ratings and the ability to adjust to 1,200 amps and higher. Fuse applications in Section 240.67 advise that arc reduction technologies are required on applications when a fuse is rated 1,200 amps and above, and only when arcing currents have a clearing time greater than 0.07 seconds. Whether fuse or circuit breaker, an arcing current evaluation must be conducted, documented and made available.
First introduced in 2017, “arcing current” is a term the NEC has yet to define. An informational note was added to NEC 2017, referencing IEEE 1584–2002, IEEE Guide for Performing Arc Flash Hazard Calculations, as a method of providing guidance when determining arcing current.
IEEE 1584-2018 defines arcing current as, “A fault current flowing through an electrical arc plasma.” Arcing current is less than the available fault current (short-circuit current) at any point in the power distribution system due to the impedances of plasma and other materials present during an arc flash event. The additional impedance reduces current flow. This value of current will be critical in determining whether or not 240.67 and 240.87 requirements have been met, and in the case of fuses, whether or not an arc reduction technology is required.
Method to reduce clearing time
When an incident energy reduction technology is required, designers and installers may elect to use one of the following means to operate at less than the available arcing current to reduce the clearing time of larger OCPDs:
- Zone selective interlocking (240.87)
- Differential relaying (240.67 & 240.87)
- Energy-reducing maintenance switching with a local status indicator (240.67 & 240.87)
- Energy-reducing active arc flash mitigation system (240.67 & 240.87)
- An instantaneous trip setting (temporary adjustment of the instantaneous trip setting to achieve arc energy reduction is not permitted) (240.87)
- An instantaneous override (240.87)
- Current-limiting electronically actuated fuses (240.67)
An approved equivalent means is a caveat for the requirements as arc energy reduction technologies continuously improve. The code making panel did not want to limit possibilities for future technologies.
The NEC clarified two issues during the 2020 code review. First, for circuit breakers with an adjustable instantaneous pickup, a “roll-down and back up again” instantaneous trip is not permitted to meet requirements. Field modification of setpoints via dials on the face of circuit breakers is not a good idea for many reasons reviewed and discussed by the code panel. Secondly, these changes help ensure that specified technologies respond to arcing currents provide the protection desired.
3) Testing procedures
Arc energy reduction systems must now be performance tested when installed. Because some of these technologies are complex, requirements mandate that testing be performed only by qualified individuals who follow manufacturer instructions. Qualified individuals must understand that it’s possible to damage equipment during tests (e.g., injecting high currents through a fuse can open the fuse, which must then be replaced.) The qualified individual must also understand that some arc reduction technologies do not respond to current alone, demanding a mixture of tools and methods necessary to ensure proper installation.
Qualified individuals must provide a written test record and make that record available to the authority having jurisdiction. The record should be provided to the facility within which it is installed, with files available for future reference.