Edits for Clarity: Changes in emergency system sources of power and circuits in NEC chapter 7

Published On
Apr 15, 2021

Chapter 7 of the National Electrical Code includes many articles, such as Emergency Systems (Article 700); Legally Required Standby Systems (Article 701); Optional Standby Systems (Article 701); Class 1, 2, and 3 Remote Control, Signaling, and Power-Limited Circuits (Article 725); Fire Alarm Circuit Wiring (Article 760); and other special systems.

Article 700 is unique since it covers emergency systems and, as can be noticed, does not have the word “standby” in the title. Articles 701 and 702 have “standby” in their titles, which makes these articles slightly lower in the hierarchy of systems. While requirements in articles 700 and 701 are under the control of the authority having jurisdiction, only Article 700 is not for standby systems, although many people in the electrical industry mistakenly call these circuits “emergency standby circuits.”

In the 2020 NEC , there are a few changes to Article 700 that may affect design, application and installations of emergency sources of power and emergency circuits, which may also make using Article 700 much easier.

The title of 700.4 has been changed from “Capacity” to “Capacity and Rating” with subsection (B) added to the requirements for capacity. This new subsection states that an emergency system must have adequate capacity in accordance with Article 220 or by other approved methods. The building code or an energy code might be an “other approved method.”

The emergency system must be able to carry the entire emergency load at any one time, unlike other applications where the entire load may not be used simultaneously, such as some loads for hospitals, clinics and other similar healthcare facilities. The emergency system must also be able to handle any motor startup where either the motor was shut down during the 10-second or more power outage or where a motor must be started as part of the emergency, such as a fire pump, which could have a substantial amount of startup current.

In 700.5(A), a statement was added explaining that meter-mounted transfer switches are not permitted for emergency system use. Working for Underwriters Laboratories, I met with the manufacturer of meter-mounted transfer switches in the 2001–03 era, when the intent of the transfer switch was to be installed directly behind the utility meter and locked with the meter ring by the power company. These transfer switches were not designed for emergency power usage and usually were added by the power company. Text has also been added to 700.5(C) stating that transfer switches cannot be reconditioned and rebuilt.

The establishment of new subsections and titles makes for easier use and information access. A newly labeled and titled 700.12(A) addressed power source considerations. This section states that, when selecting an emergency source of power, consideration must be given to the occupancy and type of service to be rendered. For example, evacuating a theater will take a minimal amount of time, but evacuating a larger, single- or multiple-story building will take longer, especially when normal power is lost due to trouble inside or outside the building. In conjunction with 700.12(A), newly labeled 700.12(B) deals with emergency equipment design and location that was previously covered by two paragraphs that were not numbered or titled in the 2017 NEC.

Emergency equipment is required to be designed and located to minimize the hazards that might cause complete failure due to flooding, fires, icing and vandalism. An example of a catastrophic failure was Hurricane Katrina, where many of the region’s emergency systems were compromised due to heavy rain and flooding. This section also states that emergency sources of power described in 700.12(B) must be installed either in spaces fully protected by approved automatic fire protection systems or in spaces with a two-hour fire rating where located within (1) assembly occupancies for more than 1,000 persons; (2) buildings above 75 feet high with any of the following occupancies: assembly, education, residential, detention and correctional, business or mercantile; and (3) educational occupancies with more than 300 occupants.

Section 700.12(H) provides new installation requirements for DC microgrids used as emergency sources of power. These new power sources are required to be of suitable rating and capacity to supply and maintain the total emergency load for not less than two hours of full-demand operation. A DC microgrid system may not serve as the sole source of power for the emergency system where it serves as the normal supply for the building or group of buildings concerned. In other words, the microgrid may also require a generator set as a backup.

Section 700.16 in the 2020 NEC has subsection numbering and titling for easy use. Becoming familiar with Article 700 use is a must for any electrical designer, electrical contractor or electrician.

About the Author

Mark C. Ode

Fire/Life Safety, Residential and Code Contributor

Mark C. Ode is a lead engineering associate for Energy & Power Technologies at Underwriters Laboratories Inc. and can be reached at 919.949.2576 and Mark.C.Ode@ul.com.

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