National Electrical Installation Standards

Standards as High as Your Own

Thursday, March 9, 2023


Dear CQD, are MRIs allowed to be fed from the Critical Branch of a Hospital? What if it is backed up by a UPS first? Thanks in advance, Charlie Henderson


Hi Charlie, thank you for the question, as this topic often generates a lot of confusion. An MRI may be permitted to be connected to the Critical Branch. The “Critical Branch” is one of the three (3) branches of a Type 1 Essential Electrical System (EES).

Section 517.34(A) provides guidance on the purpose/function of the “Critical Branch” as to supply power for task illumination, fixed equipment, select receptacles, and select power circuits serving the spaces and functions related to patient care. Section 517.34(A)(1)-(10) lists specific equipment, receptacles, and areas permitted to be connected to the “Critical Branch”. Well, the areas and loads listed in Section 517.34(A)(1)-(10) do not specifically call out an MRI, it may be permitted if it is deemed necessary for effective facility operation and/or functions directly related to patient care. The person or entity to make this determination would be the “Healthcare Facility’s Governing Body” as defined in Section 517.2. If the Governing Body determines a specific MRI is integral providing patient care in a Category 1 space, then it could be connected to the “Critical Branch”. Additionally, the alternate source of power providing the Critical Branch needs to be sized to handle the loads served.

The UPS is not necessarily required but would be permitted. Section 517.30 requires a minimum of two (2) independent sources of power (Normal and Alternate) for an EES. Section 517.30(B)(3) permits Battery Systems to serve as the alternate source of power for all or part of the EES.  

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CHARLIE TROUT: Charles M. Trout, better known as Charlie, was a nationally known NEC® expert and author. He served on several NEC® technical committees and is past chairman of CMP-12. In 2006 Charlie was awarded the prestigious Coggeshall Award for outstanding contributions to the electrical contracting industry, codes and standards development, and technical training. Even though Charlie passed away in October of 2015, his work continues in spirit. NECA continues to maintain this question forum for its many subscribers in memory and recognition of all his significant contributions to making the NEC what it is today.

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