New requirements in NEC Sections 240.67 and 240.87 impact overcurrent protection devices (OCPDs) 1,200 amps and higher or those that can adjust to 1,200 amps and higher. These updates mandate performance testing at the time of installation. Ground-fault protection of equipment (GFPE) at service equipment is an example of an NEC requirement that mandates performance testing to ensure safety technologies are functioning correctly when installed.
With changes including performance testing per manufacturer instructions and recommended test procedures, the electrical industry will soon see significant improvements in power system design and arc flash protection performance.
Overview of changes
New text in NEC Sections 240.67 and 240.87 identifies that, when technologies are installed to reduce incident energy, technicians must conduct performance testing at the time of installation. In addition, changes make clear to installers, designers, inspectors and equipment owners that requirements regarding larger OCPDs must respond to lower arcing currents that can occur in equipment.
The arc reduction requirements that began as part of the NEC 2011 code review took a significant step forward in NEC 2020, with changes found in three key areas:
- Installation documentation
- Safety methodologies
- Testing procedures
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.
The rationale for change
Energy reduction requirements evolved with debate and due process of language improvements. While language was first introduced in 2011, it's my opinion that a focus on performance testing wasn't possible until today—code panel members and others in the industry needed time to reach a language consensus. Some argue more should be done, but I believe the overall intent is heading in the right direction.
During the 2020 code review, the code panel and others determined the NEC had to assure technologies are installed and that they are installed correctly at the time of installation, as is done with GFPE. The NEC requires GFPE testing (for equipment protection) when installed, yet did not require performance testing on installed worker-safety technologies.
The code making panel governing GFPE requirements for devices 1,000 amps and above (found in Sections 210, 215, 230 and 240) is the same code panel responsible for Sections 240.67 and 240.87. In some sense, 240.67 and 240.87 requirements are merely a continuation of what began with the GFPE requirements of NEC Section 230.95. Those requirements entered the NEC in 1971, but it wasn't until NEC 1978 that performance requirements at the time of installation were put in place. Section 240.87 followed a similar track. It entered the NEC in 2011; after three code review cycles, the NEC finally began discussing performance testing requirements at the time of installation.
Performance testing is a line item one can't afford to miss when bidding a project. The equipment and performance testing process of GFPE and arc reduction technologies can add significant cost if forgotten. It's essential to address their requirements upfront to maximize project efficiencies.
Here are some things to consider when developing a plan to meet NEC 2020 performance testing requirements:
Combine new performance testing requirements with those of GFPE (230.95 for OCPDs 1,000 amps and above). Projects must have on-site equipment to perform GFPE testing. This equipment can also be used to conduct additional testing for arc reduction.
The zones of protection offered by each technology are important to understand; test results may not make sense otherwise. Make sure you follow manufacturer instructions to test solutions correctly.
Arcing currents are a function of available short-circuit current and can be quite high. However, technicians do not need to inject high currents to prove that transformers are installed properly and electronic trip units operate correctly. Verifying the entire system with a mix of low primary current injection testing and secondary current injection testing is the safest and most efficient method for success.
Technologies like arc quenching equipment and active arc flash mitigation systems require more than primary current injection testing to ensure functionality. Light sources and manufacturer testing fixtures may be required.
What might the future hold?
The success of safety to a three-legged stool; one leg is no more important than the others. Today, three critical documents work in unison: the NEC (NFPA 70) provides installation requirements; NFPA 70E provides requirements for safe work practices; NFPA 70B reminds us of the critical role maintenance plays over time. Today the NEC mandates arc reduction technologies and requires assurances that these technologies work at the time of installation. 70E instructs all to leverage these technologies when justified energized work is performed, and 70B dictates periodic testing of these technologies throughout the life of the installation.
As equipment ages, and as devices are removed from and added to power systems, arcing currents change. Designers must remember to update single-line diagrams and systems analysis studies and make sure the technologies effectively provide arc energy reduction well after installation. In short, proper maintenance is vital.
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