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.

By Tom Divine, PE, LEED AP, Smith Seckman Reid Inc., Houston June 10, 2016

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.

Article 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.

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.

NEC Article 700.4(B) echoes this requirement almost exactly, using substantially identical language. NEC Article 701.4 has a similar requirement, permitting the system that serves legally required standby to serve optional loads as well, with load shedding. NEC Article 517.30(B)(3) and NFPA 99, Chapter both require a predictive scheme to inhibit connection of optional loads that will overload the generating system, and automatic shedding of those loads to avoid overload, but do not otherwise describe load-shedding requirements. NFPA 110, Chapter 7.1.5 describes similar requirements with the exception that load priorities are Level 1, Level 2, and optional loads, in that order, where Level 1 loads are those whose loss could result in serious injury or death.

It’s beyond the scope of this article, but certainly worth noting that using a generator system for peak load shaving will trigger extensive additional emissions requirements for the engine generators. Emissions requirements for emergency standby gensets are much less stringent than for nonemergency units. Operation when utility power is available, for purposes other than testing, will push the generators into the more restricted nonemergency tiers.
• A COPS can be used for peak load shaving, provided that it has either adequate capacity for all its loads or has selective load shedding and pickup as required in NEC Article 708.22(B). NEC Article 700.4(B) allows peak shaving with identical language. NEC Articles 701 and 517 are silent on this issue. NFPA 99, Chapter allows for the generating system to be used for peak demand control or for other purposes, but requires that systems used in this manner have at least two gensets installed and that the system is able to support the most critical loads with the largest unit out of service. NFPA 110, Chapter 7.1.5 allows peak shaving.
• A COPS must be able to provide alternate power to operate the DCOA at full load for a period of at least 72 hours. There is no direct requirement that adequate fuel for this period of operation must be stored onsite. It’s not clear whether a dual-fuel system with utility natural gas and limited onsite diesel storage would comply. NEC Article 708.20(F)(3) prohibits the system from being solely dependent on utility gas, and NEC Article 708.20(F)(7) requires onsite fuel storage, but neither specifically requires that the system be capable of operation for the full required duration with only onsite fuel. A case can be made for some facilities-for example, those not subject to seismic disasters-that a limited-period diesel operation will allow sufficient time for gas service to be restored, reducing the amount of fuel required onsite, as described in NEC Article 708.22(C).
NEC Articles 700.12(B)(2) and 701.12(B)(2) both require that an internal combustion engine has "an on-premises fuel supply sufficient for not less than 2 hours of full-demand operation." NEC Article 517 does not address fuel supplies. NFPA 99 references requirements in NFPA 110. NFPA 110, Chapter 5.1.1: Exception, requires enough onsite fuel storage to deliver full output of the generator for the system’s class with automatic transfer between fuel sources.
• Transfer equipment must operate automatically, be identified for emergency use, and be designed to prevent inadvertent connection of the normal and alternate sources. Automatic transfer switches must be listed for emergency use and be electrically operated and mechanically held. Bypass isolation switches are permitted in accordance with NEC Article 708.24(A), (B), and (C).

NEC Articles 700.5(A), (B), and (C); and 701.5(A), (B), and (C), have nearly identical requirements, using substantially the same language. NEC Article 517.25(B)(2) describes general requirements for transfer switches, citing "reliability, design, and load considerations," and references NFPA 110. NFPA 99, Chapters,, and together describe similar requirements, along with a more extensive list of automatic transfer switch installation requirements and performance criteria. NFPA 110 devotes an entire chapter to automatic transfer switch requirements, of which Chapters 6.1.6 and 6.2.3 describe requirements similar to those for COPS switches.

• When the normal supply fails, the alternate source must be available within the time required for the application. For data applications, that time will be very short, requiring a UPS in conjunction with generation to avoid data loss. For other applications, such as fire and police stations or emergency treatment clinics, that time can be considerably longer, as described in NEC Article 708.20(A).

NEC Articles 700 and 701 also require that power must be available within the time required by the application, but also impose additional requirements. NEC Article 700.12 requires power to emergency lighting and power within 10 seconds of a normal supply outage, and Article 701.12 requires power within 60 seconds. NFPA 99, Chapter calls for service to the life safety and critical branches within 10 seconds. Paragraph declares that Type 1 essential electrical systems, as defined in NFPA 99, must be classified as Type 10 generator sets as defined in NFPA 110—another requirement for 10-second availability. NFPA 110 doesn’t define a particular pickup time. Instead, Chapter 5.4 requires that the system has capacity to pick up and carry the load in accordance with its NFPA 110 type, as described in Table 4.1(b).

• Transfer equipment serving COPS loads must not serve any non-COPS loads, as per NEC Article 708.24(D).

NEC Article 700.5(D) describes a similar prohibition against serving nonemergency loads from an emergency system transfer switch. NEC Article 701 does not contain such a restriction. A similar requirement is implicit in Article 517.32, in which the loads to be connected to the life safety branch are prescriptively described: Only the listed loads may be served from the life safety branch. NEC Article 517.33 describes the critical branch similarly, though in more permissive terms. NFPA 99, Paragraphs and describe very similar rules. No such requirement appears in NFPA 110.

Wiring and installation

Most of the COPS installation requirements will be familiar to designers of emergency systems and health care systems. COPS feeders require separation from other systems, protection from physical damage, and protection from fire (see Figure 2). Those requirements can be found in NEC Article 708.10(C). Fire protection requirements are more explicit than those for emergency systems, as described in NEC Article 700.10(D)(1). Emergency feeders installed in fully sprinklered spaces or areas do not require additional fire protection. COPS circuits, however, either must be inside a fire-resistant enclosure or be a listed electrical circuit protective system.

The meaning of "spaces or areas" in the context of NEC Article 700.10(D)(1) is not entirely clear. Previous editions of the NEC have considered emergency feeders installed in fully sprinklered buildings to be adequately protected. The NEC Handbook, in recent editions, has alternately interpreted spaces or areas to exclude spaces above ceilings, to include those spaces, and then to exclude those spaces again in the 2014 edition, calling for direct fire protection of feeders installed above ceilings. While the NEC Handbook is not code, its contents have significant influence on how the provisions of the NEC are enforced. For health care applications, the difference between fire protection requirements for emergency feeders may be more of academic than practical interest. NFPA 99 and NEC Article 517 apply the requirements of Article 700 to the life safety branch. However, NFPA 99, Paragraph explicitly exempts the life safety branch from the feeder fire protection requirements of NEC Article 700.

COPS branch circuits installed outside the DCOA also must be protected from physical damage and fire, while branch circuits within the DCOA can be installed with traditional wiring methods, as described in NEC Article 708.10(D). COPS feeder distribution equipment including transfer switches, panels, and transformers must be installed in spaces with a 2-hour fire-resistance rating. NEC Article 700.10(D)(2) has a similar requirement, but permits emergency feeder distribution in spaces protected by fire suppression systems as an alternative. NFPA 99, Paragraph exempts the life safety branch from compliance with this requirement.

COPS feeder distribution equipment also must be installed above the 100-year flood plain. NEC Article 700 requires consideration of flood hazards, but does not make any specific requirements for the installation based on flood probability, predictions, or historical flood records (see Figure 3). The elevation of the 100-year flood plain is not static in the long term. It moves up and down, and in urban areas, it generally moves up as construction replaces porous surfaces with more impervious paved and landscaped areas. It is not clear what remediation may be required as future maps are redrawn to show the elevation of COPS feeder distribution equipment below the 100-year plain.

When feeders themselves are installed below the 100-year flood plain, the installation must be treated as a wet location by using conductors with insulation listed for wet locations and wiring methods permitted for wet location installations, according to NEC Article 708.10(C)(3).

A hypothetical COPS

Figure 4 shows an abbreviated one-line diagram for a hypothetical facility with a COPS component, along with emergency loads and legally required standby loads. Some detail is necessarily omitted from the drawing to maintain legibility. COPS circuits and equipment are identified with the acronym "COPS" in their names, emergency with "EM," and legally required standby with "LRS." Circuits downstream from switch SW COPS must be separated from all other circuits, as must circuits downstream from SW EM. Legally required standby circuits, served from SW LRS, may be run in raceways and other enclosures with normal power circuits. Ground fault protection is provided by long-time, short-time, instantaneous, and ground fault (LSIG) breakers in the normal service panel, in accordance with the requirement for a second level of ground fault where one level is provided. COPS, emergency, and legally required standby circuits do not have ground fault protection, but they do have ground fault alarms.

The NEC spectrum

NEC requirements for COPS are generally similar to requirements for other robust standby power systems: emergency, legally required standby, and health care systems. And, in many particulars, those requirements differ. Emergency systems stand at one end of the spectrum; they’re built for speed and they finish their runs in a couple of hours. COPS are at the other end, built for endurance and with some of the most rigorous requirements in the NEC.

Tom Divine is a senior electrical engineer and project manager at Smith Seckman Reid Inc. He is a frequent contributor to Consulting-Specifying Engineer magazine and Pure Power and is often a speaker at Consulting-Specifying Engineer webcasts.