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Type 1 Emergency Electrical System - CMS

What type of emergency electrical system is required for an ambulatory surgical center?

Any examples are for illustrative purposes only. 

For ambulatory surgical centers and outpatient surgical departments that use The Joint Commission deemed status option, that were constructed, or had a change in occupancy type, or have undergone an electrical system upgrade since 1983, a Type 1 or Type 3 essential electrical system is required as defined in the 2012 edition of NFPA 99. 

This essential electrical system must be divided into three branches, including the:
  • life safety branch
  • critical branch
  • equipment branch
Both the life safety branch and the critical branch are kept independent of all other wiring and equipment, and transfer within 10 seconds of an electrical interruption.  Each branch has at least one automatic transfer switch.

Type 1 essential electrical system is required for:
  • Critical care areas are those special care units in which patients are intended to be subjected to invasive procedures using electrical patient care medical equipment.  Type 1 systems should be installed where there would be a risk of death or serious injury to the patient in the event of power failure.
Type 3 essential electrical system is permitted:
  • To supply emergency power in facilities that do not provide electrical life support or use general anesthesia.  Type 3 systems are permitted where equipment failure is less critical to human life and safety.
A Type 3 system is not permitted where a Type I system is required.

Additional Resources:
NFPA 99-2012:, 6.4.1,, 6.6.3
CMS S&C 07-21
Last updated on March 04, 2021
Manual: Critical Access Hospital
Chapter: Environment of Care EC

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