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517.30 Sources of Power. (Health Care Facilities)

Revision and New

Change Summary

  • Requirements for two independent sources of power and an alternate source of power for the essential electrical system for hospitals and other health care facilities were revised and relocated to 517.30. Fuel cell systems will now be permitted to serve as the alternate source for all or part of an essential electrical system.
NEC® Text

517.35 517.30 Sources of Power.
(A) Two Independent Power Sources.

Essential electrical systems shall have a minimum of the following two independent sources of power: a normal source generally supplying the entire electrical system and one or more alternate source(s) for use when the normal source is interrupted. [99: 6.4.1.1.4]

(B) Alternate Source Types of Power Sources. The alternate source of power shall be one of the following:
(1) Generating Units. Generator(s) driven by some form of prime mover(s) and located on the premises Where the normal source consists of generating units on the premises, the alternate source shall be either another generating set or an external utility service. [99:6.4.1.1.5] 
(2) Another generating unit(s) where the normal source consists of a generating unit(s) located on the premises
(3) An external utility service when the normal source consists of a generating unit(s) located on the premises
(4) A battery system located on the premises [99:6.4.1.2]
(2) Fuel Cell Systems. Fuel cell systems shall be permitted to serve as the alternate source for all or part of an essential electrical system, provided the following conditions apply:
(1) Installation of fuel cells shall comply with the requirements in Parts I through VII of Article 692 for 1000 volts or less and Part VIII for over 1000 volts.

Informational Note: For information on installation of stationary fuel cells, see NFPA 853-2015, Standard for Installation of Stationary Fuel Cell Power Systems. [99:6.4.1.1.7]

(2) N + 1 units shall be provided where N units have sufficient capacity to supply the demand loads of the portion of the system served. [99:6.4.1.7.2]
(3) System shall be able to assume loads within 10 seconds of loss of normal power source.
(4) System shall have a continuing source of fuel supply, together with sufficient on-site fuel storage for the essential system type.
(5) A connection shall be provided for a portable diesel generator to supply life safety and critical portions of the distribution system. [99: 6.4.1.1.7.5(1) through (5)]
(6) Fuel cell systems shall be listed for emergency system use.
(C) Location of Essential Electrical System Components.
Careful consideration shall be given to the location of the spaces housing the components of the Essential electrical system components shall be located to minimize interruptions caused by natural forces common to the area (e.g., storms, floods, earthquakes, or hazards created by adjoining structures or activities). Consideration shall also be given to the Installations of electrical services shall be located to reduce possible interruption of normal electrical services resulting from similar causes as well as possible disruption of normal electrical service due to internal wiring and equipment failures. Consideration shall be given to the Feeders shall be located to provide physical separation of the main feeders of the alternate source from the main feeders of the normal electrical source to prevent possible simultaneous interruption.

Informational Note: Facilities in which the normal source of power is supplied by two or more separate central station-fed services experience greater than normal electrical service reliability than those with only a single feed. Such a dual source of normal power consists of two or more electrical services fed from separate generator sets or a utility distribution network that has multiple power input sources and is arranged to provide mechanical and electrical separation so that a fault between the facility and the generating sources is not likely to cause an interruption of more than one of the facility service feeders.

Copyright© 2016 National Fire Protection Association
(See NEC for complete text)

Expert Analysis

When reviewing the requirements of 517.35 from the 2014 NEC, the electrical power sources for the essential electrical system of a health care facility must be supplied by a minimum of two independent sources; a normal power source and one or more alternate power sources for use when the normal power source is interrupted. The normal power source is generally made up of a source supplied by the local electric utility power company and an on-site power generator(s), which can be a private on-site power generator unit(s) or another electric utility-supplied source. The alternate power source was permitted to be one of several options.

Typically, the alternate sources of power are supplied to the loads through a series of automatic and/or manual transfer switches. The transfer switches can be non-delayed automatic, delayed automatic, or manual transfer depending on the requirements of the specific branch of the essential electrical system that they are feeding. It is permissible to feed multiple branches or systems of the essential electrical system from a single automatic transfer switch provided that the maximum demand on the essential electrical system not exceed 150 kVA.

One of the most noticeable changes to the requirements for the types of allowed power sources for these essential electrical systems was the added language at 517.30(B)(2) for fuel cell systems. Fuel cell systems will now be permitted to serve as the alternate source or all or part of an essential electrical system, with six specific conditions involved [see 517.30(B)(2)(1) through (6)]. Fuel cells provide a high level of reliability and have a proven reliability track record in data centers and other mission-critical facilities. Other advantages to fuel cells include the fact that a failed fuel cell can be isolated and replaced without shutting down the entire string, and they have fuel flexibility from natural gas to diesel.

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