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Emergency vs. Standby Systems: What is the Difference?


The term “Emergency Generator” is often used incorrectly to describe the generator used to provide backup power to a facility. Officially, as defined by NFPA 70, National Electrical Code (NEC), there are four types of backup or standby power systems: Emergency Systems, Legally Required Standby Systems, Optional Standby Systems and Critical Operations Power Systems (COPS). Understanding the differences among these system classifications is important for determining which codes and standards apply and for what the design, installation, inspection, maintenance and testing requirements are for the backup power system.

  • Emergency Systems (NEC Article 700), which are legally required for some facilities, are systems whose operations are essential for safety to human life. These are also known as Level 1, or critical to life safety.
  • Legally Required Standby Systems (NEC Article 701) are required by codes to illuminate or to power equipment that is not categorized as requiring emergency power, but whose failure could create hazards, hinder rescue or hamper firefighting operations. These systems are known as Level 2, or less critical systems.
  • Optional Standby Systems (NEC Article 702) are not required by code and serve equipment whose failure will not impact life safety. These systems may be specified and installed to protect against economic loss or business operations. The optional standby system is least stringent from a code standpoint, but can be “business critical.” End users may choose to voluntarily apply the more stringent emergency and legally required standards, depending on their tolerance for downtime in the event of a utility outage.
  • Critical Operations Power Systems (NEC Article 708) were added as a classification in the 2008 NEC edition in response to the 9/11 terrorist attacks and the Hurricane Katrina disaster. These systems are required in facilities that, if destroyed or incapacitated, would disrupt national security, the economy or public health or safety. Government agencies or Authorities Having Jurisdiction (AHJ) can designate any critical facility ‒ such as police stations, fire stations, emergency call centers, telecommunications carriers, data centers and other critical infrastructure ‒ as a “designated critical operations area” to comply with Article 708.

There are big differences between these types of systems. When communicating with the code officials or AHJ, it is important to use the correct term – emergency or standby. In some cases, a single system may be used to power both emergency and legally required or optional loads. In these cases, the more stringent code requirements of the most critical classification will apply and special considerations must be made when designing, installing and testing these systems to ensure code compliance with maintainability and economics in mind. The most detailed requirements typically apply to hospitals and health care facilities.

The basic requirement for the type of system comes from the building or fire codes followed by the local AHJ. Whether they follow NFPA 5000, Building Construction and Safety Code; NFPA 1, Fire Code; NFPA 101, Life Safety Code, the National Building Code (NBC), the International Building Code (IBC) or the International Fire Code (IFC), the requirements are relatively consistent. Once it is determined that emergency or legally required standby power is dictated by the code, the NEC and NFPA 110, Standard for Emergency and Standby Power Systems and other NFPA codes define the basic requirements for the system.

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