Putting COPS into context

NFPA 70: National Electrical Code Article 708: Critical Operations Power Systems (COPS) introduced electrical standards for facilities that support critical functions in response to vulnerabilities from natural and human-initiated disasters. However, these standards are less than straightforward and seemingly contradictory with other codes. It’s time to put COPS into context.


This article is peer-reviewed.Learning objectives

  • Be aware of the definitions associated with critical operations power systems (COPS).
  • Understand specific requirements for COPS installation
  • Explain the differences between emergency systems and COPS, and the nuances thereof.

Figure 1: Critical operations power systems (COPS) are generally installed in vital infrastructure facilities that, if destroyed or incapacitated, would disrupt national security, the economy, public health or safety, and where enhanced electrical infrastArticle 708: Critical Operations Power Systems (COPS) first appeared in the 2008 edition of NFPA 70: National Electrical Code (NEC). At that time, recent events in the U.S. had highlighted vulnerabilities of critical systems and functions to natural and human-initiated disasters. Article 708 was developed to establish effective electrical standards for facilities that support critical functions, to ensure the continuity of essential services and to maintain the ability to recover from disastrous events (see Figure 1).


Article 708 introduced three new acronyms to the NEC. As one would expect for an electrical code, terms are defined by their electrical, rather than functional, characteristics in 708.2:

• "COPS" is an electrical system serving part or all of a facility that must operate continuously to support public safety, emergency management, national security, or business continuity. The requirement for a COPS is determined by governmental authorities in accordance with codes or statutes, or by facility engineering documentation.

• A "designated critical operations area" (DCOA) is an area that, by virtue of the functions performed within it, requires a COPS. Examples include air traffic control centers, police and fire stations, 911 call centers, communication centers, business data-processing centers, and broadcast stations. The NEC, as an installation code, doesn't determine which facilities require a COPS. Instead, it describes how the system must be installed.

• "Supervisory control and data acquisition" (SCADA) is a control and monitoring system for the COPS. Long used in industry, this term is new to the NEC with Article 708. It's defined in the Article, but doesn't appear among the requirements. Informative Annex G lists requirements for a SCADA system, but these provisions are informational rather than prescriptive. Those requirements, though, are not code; they amount to suggestions for how a SCADA system might be installed. For now, in the NEC, SCADA is an acronym without requirements.

Documentation requirements

NEC Article 708 describes a number of documentation requirements including a risk assessment, a hazard-mitigation strategy, and maintenance and testing records. These elements won't be addressed here, as readers of this article are likely to be primarily concerned with COPS installation requirements, particularly for the emergency power supply system as defined in NFPA 110: Standard for Emergency and Standby Power Systems.

Figure 2: COPS feeders require separation from other systems, protection from physical damage, and protection from fire. A fire-rated conductor with RHH insulation and 600-kcmil copper is shown on the left. A similar THHN conductor is shown on the right.

Standby power

NEC Article 708 permits storage batteries, uninterruptible power supplies (UPSs), and fuel cell systems as alternate sources for COPS. These systems are uneconomical and unwieldy for all but a minority of COPS applications. Typically, the project characteristics will strongly push the alternate source selection toward generators. Generator requirements in Article 708 will largely be familiar to designers of emergency systems and health care facilities, as they generally echo similar requirements from other articles that cover those systems. Emergency, health care, and critical operations power systems face similar challenges: They must be robust and reliable, and their components must be resistant to detrimental changes when not in operation. At the same time, their operational environments are different: Emergency systems need to operate only for a limited time to protect occupants while health care systems must operate longer to protect patients, and COPS must operate for long periods to protect the interests and safety of persons outside their facilities. Below, some of the requirements for COPS generating systems are compared to requirements for emergency systems as defined in NEC Article 700, legally required standby systems as defined in NEC Article 701, and health care facilities as described in NEC Article 517 and NFPA 99. References are from these codes:

• NEC-2014

• NFPA 110-2013.

References appearing as paragraph descriptors only are from the NEC. References from other codes will be preceded by the NFPA designation of the code.

• Prime mover(s) must start automatically when normal electrical service is lost. The system must be able to delay at least 15 minutes before returning to normal service after an outage and restoration, according to NEC Article 708.20(F)(1).

These requirements are nearly identical to requirements for emergency systems and legally required standby systems in Article 700.12(B)(1) and in Article 701.12. (B)(1), respectively. Article 517.31 requires that the life safety and critical branches be connected automatically, but does not address time delay on retransfer to normal service. NFPA 99 requires an adjustable delay for retransfer, but does not define a specific lower limit in Article NFPA 110, Article 6.2.8 requires an unspecified retransfer delay, and the explanatory material of Annex A recommends a setting of 30 minutes.

• Generator fuel-transfer pumps must be served by the COPS as required in Article 708.20(F)(2).

A specific requirement that fuel-transfer pumps be served from the systems they support appears in Articles 700.12(B)(2) and 701.12(B)(2). NFPA 99, Chapter and NFPA 110, Article 7.12.5 require that all necessary ac-powered accessories be served from load terminals of transfer switches or directly from the generator while NEC Article 517.32(F) requires these accessories to be connected to the life safety branch.

• Generators cannot rely solely on gas from a public utility as their fuel supply. If they use utility gas, they must have at least one other fuel source. Similarly, they must not rely solely on a municipal water supply for engine cooling. Where an additional source of fuel or cooling is required, NEC Article 708.20(F)(3) requires that the transfer between sources be automatic.

Articles 700.12(B)(3) and 701.12(B)(3) have substantially similar requirements. NEC Article 517; NFPA 99; and NFPA 110 do not prohibit reliance on utility gas as the sole fuel supply.

• NEC Article 708.20(F)(4) describes requirements for certain auxiliary equipment. Where battery power is used for starting or controlling generators, batteries must be automatically charged independently of the generators. Where battery power is necessary for generator operation, the charger must be connected to the COPS. Where ventilation dampers are electrically operated, their power source must be connected to the COPS.

A similar set of requirements appears in NEC Articles 700.12(B)(4) and 701.12(B)(4). NEC Article 517; NFPA 99; and NFPA 110 require standby power for necessary accessories, as described earlier. NFPA 110, Chapter requires battery-charging equipment driven directly by the prime mover, and Chapter requires at least one more charger.

• Where a single generator supplies the COPS, the system must include a means to connect an additional generator as per NEC Article 708.20(F)(6).

NEC Article 700.4 requires a temporary or portable unit whenever the emergency generator is out of service. This requirement does not appear in Articles 517, 701, or NFPA 110. NFPA 99, Chapter does include a requirement for a portable generator connection when fuel cells are used as the alternate source, but has no such requirement for generator-based systems.

• Where the prime mover is an internal combustion engine, there must be an onsite supply of fuel, protected and secured in accordance with the risk assessment for the facility as per NEC Article 708.20(F)(7).

Requirements for onsite fuel appear in NEC Articles 700.12(B)(2) and 701.12(B)(2). No such requirements appear in NEC Article 517; NFPA 99; or NFPA 110.

• NEC Article 708.22(A) requires that the alternate source's capacity and rating be sufficient for all loads to be operated simultaneously for continuous operation with variable load for an unlimited number of hours. This requirement allows the standby system to be sized to serve the actual load of the DCOA, as opposed to its maximum theoretical load, allowing the designer to take advantage of noncoincident loads and other realistic diversity factors. It also allows the system to be rated for standby service rather than prime service.

NEC Article 700.4 requires the emergency system to be rated to serve all loads simultaneously without reference to variable loads. NEC Article 701.4 calls for a rating to serve "all equipment intended to be operated at one time," allowing for some diversity. Both NFPA 99, Chapter and NEC Article 517.30(D) require systems to be rated "to meet the maximum actual demand likely to be produced by the connected load." NEC Article 517.30(D) provides a list of considerations for determining the capacity of the generating system but does not prescribe any particular formula. It also specifically exempts hospital systems from compliance with NEC Articles 700.4 and 701.4. NFPA 110 requires adequate capacity to pick up and carry their loads within the time period determined by their type classification.

• NEC Article 708.22(B) permits the COPS alternate source to serve additional load types—including emergency, legally required standby, and optional loads—if it has adequate capacity for all the loads or has automatic load-shed and pickup functions to selectively drop lower-priority loads if the system approaches overload. COPS and emergency circuits have the highest priority—without differentiation—followed by legally required standby loads and, finally, optional loads.

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