Mission-Critical Wiring

At a recent training presentation on wiring for healthcare facilities, there was a question about protection for the emergency system in a hospital. An attendee asked if the emergency lighting circuits installed for 2-by-4-foot lay-in luminaires located in a suspended ceiling grid could be wired using MC cable or if they needed to be wired using metal raceway, such as EMT. This question comes up fairly often. The simple answer is no. MC cable is not permitted to be used for the emergency lighting system wiring as described in the question. This article provides the reasoning and National Electrical Code (NEC) justification to support the answer.

Defined terms

A few fundamentals must be reviewed to provide a thorough response. First, the definitions in 517.2 can assist with application of the appropriate part and sections of the NEC. Since this topic is related to a hospital, Article 517 applies; more specifically for an emergency system of a hospital, Part III of Article 517 is applicable. The term “emergency system” is defined in 517.2 as “a system of circuits and equipment intended to supply alternate power to a limited number of prescribed functions vital to the protection of life and safety.” Part III of Article 517 provides the requirements for the essential electrical system of healthcare facilities. Section 517.30 addresses hospital essential electrical systems.

Section 517.30(B)(2) describes the “emergency system” as the circuits connected to the life safety branch and critical branch. Since a hospital’s emergency lighting is connected to the life safety branch and is part of the emergency system, the mechanical protection requirements in 517.30(C)(3) must be applied. Section 517.30(C)(1) requires separation of the emergency circuit wiring from the normal circuits. This is to reduce possibilities of a failure in a normal circuit causing the failure of an emergency circuit. Some conditions permit the emergency circuits within the same enclosure as the normal circuits as provided in 517.30(C)(1) list items 1 through 4.

The question relates to mechanical protection of the emergency lighting circuits for lay-in fixtures in a hospital. The purpose of this is to reduce possibilities of damage to life safety and critical branch wiring and provide mechanical protection to circuits that are part of the emergency system. This concept is often referred to as a “defend in place” philosophy because many of the occupants in the hospital, such as patients and staff members, cannot normally exit during an emergency. The Code requires this hardened wiring and protection to minimize the risk of physical damage and failure to these important circuits, and it applies to both feeders and branch circuits.

A review of 517.30(C)(3), items (1) through (5), shows no allowance for MC cable to be used as described in the question. The only provision that comes close is list item (3)(d) to 517.30(C)(3). This list item would allow the MC cable to be used in this application if the MC cable were installed because it was necessary for a flexible connection. This is not the case in the question. It is not necessary to connect a lay-in style luminaire in a suspended ceiling grid with MC cable. It can be accomplished using a nonflexible metal raceway, MI cable or other wiring method provided in 517.30(C)(1). A flexible wiring method used in a lay-in-style ceiling as described in the question appears to indicate that the flexibility would be more for convenience of installation rather than necessity. Many technicians in the field get used to doing things a certain way, and when wiring in a special occupancy, they may lose track of more restrictive requirements.

Flexible metal wiring methods

Listed flexible metal raceways, listed MC cable and listed AC cables are permitted to be installed for emergency circuit as wiring in listed prefabricated medical headwalls and in listed office furnishings, where fished into existing walls or ceilings, not otherwise accessible and not subject to physical damage, and if it is necessary for flexible connection to equipment. There are no exceptions to this rule.


Branch-circuit and feeder wiring that is part of the emergency system in a hospital must be mechanically protected by being installed in a wiring method as specified in any of the list items (1) through (5) to 517.30(C)(3). The emergency system in a hospital includes the life safety branch and the critical branch systems. Emergency lighting is connected to the life safety branch. Emergency systems in hospitals are typically governed under an engineering design as well. Always check with the engineer of record and applicable authority having jurisdiction (AHJ) for specific local requirements and interpretations. As provided in 90.4, the AHJ has the final interpretation and approving responsibilities.

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 mj@necanet.org.

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