NFPA 99, NFPA 101, and NFPA 110 establish the minimum requirements for defining the level, type, and class of EPSS.
Level: The EPSS level defines powered loads and risk to human life and safety.
Level 1: Equipment failure could result in loss of life or serious injury.
Level 2: Equipment failure is less likely to result in loss of life or serious injury.
Type: The EPSS type determines the maximum time in seconds that essential ATS load terminals can be without power.
Type 10: 10 sec to restore power
Type 60: 60 sec to restore power.
Class: The EPSS class determines the minimum time, typically in hours, that the EPSS can operate without being refueled.
Class 6: 6 hr of operation
Class X: X hr of operation as required by application, code, or user.