Environment of Care (EC) (Critical Access Hospitals / Critical Access Hospitals)
Emergency Power Systems - Types
Publish | January 01, 0001
What is the distinction between emergency generators and stored emergency power supply systems (SEPSS) and when is one used versus the other?
The loads defined by EC.02.05.03 require a reliable emergency power source. Stored-energy emergency power supply systems (SEPSS) are one means to automatically supply emergency power to critical loads. Per NFPA 111, a SEPSS consists of an uninterruptible power systems (UPS), a rectifier plant, or a motor generator powered by a stored electrical energy source; a transfer switch designed to monitor preferred and alternate load power source and provide desired switching of the load; and all necessary control equipment to make the system functional. Per NFPA 99 (1999 edition), restoration of critical loads are required within 10 seconds. If an UPS is installed to condition power or supply power when normal power is interrupted until emergency power from a generator or normal power is re-established, the UPS is considered a bridging device, and typically not a SEPSS. An assessment should be made as to whether the UPS operation, during that time of bridging to emergency/normal power is for safety to human life, or if interruption during that time of bridging would produce serious life safety or health hazards to patients, the public, or staff. If certain criteria are met and applied during the time of bridging, then the organization may choose to classify the UPS as a SEPSS. See applicable NOTE within EC.02.05.07 for more details. If the criteria apply to a UPS that is a stand-alone device with no connection to an emergency power source like a generator, then the UPS is to be classified as a SEPSS when applied as follows. The NFPA 99 (1999) evaluation process starts from the occupancy chapter, Chapters 12 through 20. If the occupancy chapter requires a Type 1 essential electrical system, then section 3-4 is used, which allows for an emergency generator or battery to power the Type 1 EES. A battery system is permitted if it meets all the requirements of a Type I EES and complies with the National Electrical Code (NEC) NFPA 70, Article 700, and batteries must also meet the requirements of NFPA 111 Stored Electrical Energy and Standby Power Systems. So essentially, a SEPSS can replace a generator with a Type 1 emergency power distribution system if properly configured. [EC.02.05.07]
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