Learn about the most significant new and updated 2017 NEC requirements and how they impact you regarding available short-circuit current ratings.
By Tim Crnko, technical sales and Dan Kuzma, senior analyst, Bussmann by Eaton
Editor’s Note: This article is adapted from the white paper, “Code changes affecting Short-Circuit Current Ratings based on the 2017 NEC®.” Download the full paper to get additional information on other NEC code revisions and additions about adjustable-speed drive SCCRs, the changing UL standards for protecting power electronic conversion equipment, and more.
SCCR is an equipment rating pertaining to safety under fault current conditions. Failure to apply equipment SCCRs properly can result in serious safety hazards.
Why is SCCR important? It’s about safety. Both the National Electrical Code® (NEC®) and Occupational Safety and Health Administration (OSHA) requirements for SCCR prohibit having any equipment located at a point in an electrical system where the available short-circuit current is greater than what the equipment can withstand. This applies to new equipment installations and existing equipment installations, or if it’s moved around within a single facility or multiple facilities.
Let’s examine some specific 2017 NEC SCCR requirement changes.
Chapter 1 General, Article 110 Requirements for Electrical Installations, Part I. General, 110.24 Available Fault Current and 110.24(A) Field Marking
REVISION. This change is significant because the change requires documentation for the maximum available short-circuit current calculation be available to those authorized to design, install, inspect, maintain or operate the system.
Section 110.24(B) continues to require service equipment to be field marked with the available short-circuit current along with the date the calculation was performed. This doesn’t apply to dwelling units and some industrial installations. 110.24(B) requires the marking to be updated whenever system modifications are made that result in changes to the available short-circuit current.
Chapter 4 Equipment for General Use, Article 409 Industrial Control Panels, Part II. Installation, 409.22 Short-Circuit Current Rating
REVISION. This change is important because the 2014 NEC 409.22 text was moved to 409.22(A) Installation along with changing the term “available fault current” to “available short-circuit current.”
409.22(B) Documentation is entirely new. It stipulates any panel required to be marked with its SCCR in accordance 409.110(4) also must have the available short-circuit current calculated and documented, along with the date it was calculated, and made available to those authorized to inspect the installation.
409.22 doesn’t apply to industrial control panels that contain only control circuit components (not having power circuits) per 409.110(4).
Chapter 4 Equipment for General Use, Article 430 Motors, Motor Circuits, and Controllers, Part VIII. Motor Control Centers, 430.99 Available Fault Current
NEW. This new NEC section is significant because it requires:
- Calculating the available short-circuit current where a motor control center (MCC) is to be installed.
- The documentation of the available short-circuit current and the date it was calculated must be made available to the inspector or Authority Having Jurisdiction (AHJ).
This new section (see photo) works in conjunction with the already existing 430.98 that requires an MCC to be marked with its short-circuit current rating. Now, with 430.98 and 430.99 in place, it should be relatively easy for the inspector to determine if an MCC installation is complaint by comparing the MCC SCCR to the available short-circuit current.
Download the full paper to get additional information on other NEC® code revisions and additions.
Bussmann by Eaton, based in St. Louis, is a participating Encompass™ Product Partner in the Rockwell Automation PartnerNetwork™ program. The company supplies fusible circuit protection and electrical safety solutions to protect equipment and provide reliable, efficient power distribution.
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