Chapter 5: Emergency and Standby Power Systems

Introduction

Emergency electric services are required for protection of life, property, or business where loss might be the result of an interruption of the electric service. The extent of the emergency services required depends on the type of occupancy, the consequences of a power interruption, and the frequency and duration of expected power interruptions.

Municipal, state, and federal codes define minimum requirements for emergency systems for some types of public buildings and institutions. These shall be adhered to, but economics or other advantages may result in making provisions beyond these minimums (see the NEC, Articles 517, 700, 701, and 702). The following presents some of the basic information on emergency and standby power systems. For additional information, design details, and maintenance requirements, see ANSI/IEEE Standard 446 1987 ( IEEE Recommended Practice for Emergency and Standby Power Systems for Industrial and Commercial Applications ), ANSI/NFPA 110 ( Emergency and Standby Power Systems ), and ANSI/NFPA 110A ( Stored Energy Systems ).

Emergency power systems should be separated from the normal power systems by using separate raceways and panelboards. The NEC requires that each item of emergency equipment be clearly marked as to its purpose. In large public buildings, physical separation of the emergency system from the normal system elements would enhance the reliability of the emergency system in the event of fire or other contingencies. Also, more and more states are requiring that the emergency systems not only be separated from the normal systems, but that they be enclosed...