Identifying Emergency Systems: Clear marking of emergency wiring prevents problems

NEC 2020 Cover

The National Electrical Code Section 700.10(A) requires all boxes and enclosures­—including transfer switches, generators and power panels that are part of an emergency system—to be marked so they are readily identifiable as a component of the emergency system. Each aspect requires attention to detail. One thing that must be known is which wiring and which equipment and enclosures are components of an emergency system for a facility. Another is the level of detail required to accomplish the marking requirement prescribed by this NEC rule. Many installations and inspections fall short of meeting both requirements.

First, let’s review what constitutes an emergency system. Article 700 applies directly to all emergency electrical systems, and this term is defined in Section 700.2. The definition of the term applies in Article 700 and to other rules throughout the NEC that include or reference the term “emergency systems.” So, with that information, let’s take a look at how the definition narrows these systems down.

Emergency systems are legally required and usually classed as emergency by municipal, state, federal or other codes, or by any governmental jurisdictions. These systems are intended to automatically supply light and/or power to designated areas and equipment in the event of failure of the normal supply, or in the event of failure of a portion of a system intended to supply, distribute and control power and illumination essential for safety to human life.

Emergency systems are generally installed in places of assembly where illumination is required for large numbers of people to safely exit buildings, such as hotels, theaters, sports arenas, healthcare facilities and similar institutions. These systems often provide power for such functions as ventilation (where essential to maintain life), fire alarm systems, elevators, fire pumps, industrial processes and other equipment. The NEC definition of the term “emergency system” assists users in understanding how emergency systems are determined and what wiring and components in the electrical systems are for emergency purposes.

Now that a more thorough understanding of emergency systems has been established, the next Code rule to review and correctly apply is the requirement to clearly mark (identify) equipment enclosures, junction and pull boxes, panelboards, transfer switches, branch circuit and feeder wiring and so forth that are part of the emergency system. The charging language in Section 700.10(A) relates to identification, which is what this section is all about. Here is where many don’t get it right in the field. Those that are directly involved with the design or installation of the emergency system generally know which components and wiring make up the system, so that personal knowledge and what they consider acceptable marking may be inadequate for the residents and users of the facility after the building is occupied.

The words “readily identified” mean if anyone (not just someone with electrical experience) looks at the wiring or equipment enclosures, they should know it is part of the emergency system. To get this right in the field, we must include the words “emergency system” as part of the permanent marking required by 700.10(A)(1). Then it is clear to not only the installer and construction teams, but to all those that occupy and use the facility long after occupancy has been granted.

Many in the field make the mistake of just marking enclosures with the letters “EM” rather than spelling it out. Inspectors have been known to fail an installation for this inadequate marking. (As an aside, inspectors should strive to consistently apply this requirement to all qualifying emergency systems and equipment, but that’s a story for another day.)

Section 700.10(A)(2) also indicates that exposed (not concealed) cables and raceways be permanently marked as a component of the emergency system or circuit (feeders and branch circuits) at intervals not exceeding 25 feet. Finally, the receptacles supplied from an emergency system must be a distinctive color, such as red, or marked on the receptacle or cover plate to identify it as emergency.

Most design teams and electrical contractors address these requirements through their specifications or with marking methods such as engraved labels and directories. Special stickers could be used for raceways, and cables or color coding and legends could be used if acceptable to the authority having jurisdiction.

Finally, let’s look at the basic reasons for the specific marking requirements for emergency system wiring and components. One is so that owners and maintainers can distinguish emergency systems from normal power systems and equipment for servicing and other purposes. Another reason is to help with maintaining the wiring separation requirements specified in Section 700.10(B).

About the Author

Michael Johnston

Executive Director of Standards and Safety, NECA

Michael Johnston is NECA’s executive director of standards and safety. He is a member of the NEC Correlating Committee, NFPA Standards Council, IBEW, UL Electrical Council and NFPA’s Electrical Section. Reach him at

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