New unified terminology for short-circuit current and fault current will provide clarity as these terms had been used interchangeably throughout the NEC.
In parallel, new requirements were added to NEC Article 408 to support the proper application of electrical products concerning short-circuit current rating (SCCR) and interrupting ratings of overcurrent protection devices (OCPDs).
Together, these changes are important because they reduce the likelihood of electrical hazards. The SCCR calculations and equipment labels will instrumental to informing maintenance practices and future equipment upgrades.
The definition now states that “available fault current” is the highest short-circuit current that can flow at a particular point in the electrical system. “Maximum available short-circuit current” and “short-circuit current” were also changed to “available fault current.”
Previously, the NEC did not require that switchboards, switchgear and panelboards have labeled SCCR and available fault current values. Now, Article 408.6 does.
The NEC 2020 code review reaffirmed a straightforward practice that’s proven quite successful:
In my opinion, the changes offer common-sense solutions for everyday issues encountered in the field. But, as with any Code change, I expect some in our industry will have to adjust how they work over the short- and long-term.
As with any Code change, I expect some in our industry will have to adjust how they work over the short- and long-term.
Getting used to the Code
The new language “available fault current” in replace of “maximum available short-circuit current” may give some readers pause. I expect the adjustment period to be short because, while the language has changed, the intent remains the same.
Calculations are a must
This is a significant change due to the sheer volume of equipment that must now be marked with available fault current. I believe the new requirement will drive home the importance of performing fundamental equipment evaluations at install.
The way equipment is labeled may need to be examined and changed. For instance, when a panelboard is shipped, the manufacturer often has no way of knowing what OCPDs will be placed inside. The standards for these products require that a label reflect how to determine the SCCR, not the SCCR of the panel, which is dependent upon the lowest interrupting rating of the breaker that’s installed. It's up to the installer and the Authority Having Jurisdiction to determine that panelboard’s overall SCCR.
Additional SCCR marking requirements for other types of equipment during installation may come to fruition. It’s important to remember there are different levels of protection available. When equipment is clearly labeled with SCCR, it will help raise awareness that any replacements or additions should have a minimum interrupting rating per the marking. I believe this will help reduce the likelihood of a technician installing an insufficient breaker when adding a circuit or replacing a faulty device and will raise the awareness of the proper continued maintenance and servicing of equipment after the fact.
Designing big from the start
It’s vital to remember that electrical systems change and many organizations plan to expand their facilities. And while most design engineers account for growth, on commercial projects, where the bottom line is king, builders may look to the least expensive option without accommodating the future: motor additions, transformer increases and the like. In my opinion, stepping up to the next interrupting rating is a better choice than cutting it too close. I encourage all designers and contractors to closely align with customers on a comprehensive plan for their system:
I encourage all designers and contractors to closely align with customers on a comprehensive growth plan.
While the available fault current language changes and additions to Article 408 greatly enhance safe OCPD installation, I believe the NEC can do more to provide a fault current overage baseline to help all understand when to recommend increased protections. I've spoken with numerous inspectors and many feel there’s an opportunity to establish effective interrupting rating requirements, perhaps by looking to the NEC’s exploration of adding overage requirements for calculations as a guide.
My question to the NEC: can we establish fault overage guidelines for electrical designs? For instance, how close to 10,000 amps should designers get before bumping up to a 22,000-amp breaker? Would a 1,000-amp baseline suffice? Or 2,000 amps? Whether for NEC requirements or industry practice, a dialog regarding guidelines that help designers and contractors understand when it’s appropriate to go to the next level of protection to maintain safety if and when distribution systems expand would help drive change.
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