If disruption of the normal utility supply occurs, readiness of emergency power is a key consideration in safeguarding building occupants. NFPA 110: Standard for Emergency and Standby Power Systems covers performance requirements for power systems providing an alternate source of electrical power in the event that the primary power source fails. Power systems covered include power sources, transfer equipment, controls, supervisory equipment, and all related electrical and mechanical auxiliary and accessory equipment needed to supply electrical power to the load terminals of the transfer equipment.

Among the changes in the 2010 edition of NFPA 110 are:

• Clarification that the Standard is intended to apply to Level 1 or Level 2 emergency power supply systems (EPSSs)
• Operation testing and routine maintenance provisions cover new and existing EPSSs.
• Revised definitions of automatic transfer switch and non-automatic transfer switch for consistency with NFPA 111 and correlation with relevant product standards
• Revised material on Level 1 and Level 2 EPSSs clarifies the function and applicability of each type of system
• Differentiation of requirements for acceptance testing for new and unoccupied buildings versus those for existing occupied buildings and facilities. In addition, criteria for test duration, step-testing intervals, and required documentation have been modified.
• Revised rules for operational test durations for diesel and spark-ignited prime movers. Also, the 36 month test requirement has been revised to clarify the maximum duration, the minimum acceptable EPS loading or operating condition, and the method of test initiation.