Let's face it. The electric utility grid isn't 100% reliable. That's why the National Fire Protection Association (NFPA) and Code-enforcing authorities require alternate (emergency) sources of power to serve certain portions of electrical distribution systems in hospitals.

In addition to appearing in Part III of Art. 517 of the 2002 NEC, requirements for essential electrical systems can be found in Chapter 4 of NFPA 99-2002, Standard for Health Care Facilities, and other applicable federal, state, and local requirements.

According to 517.25, which applies to clinics, medical and dental offices, outpatient facilities, nursing homes, limited-care facilities, hospitals, and other health-care facilities that serve patients, essential electrical systems must be able to supply at least enough light and power for life safety in the event that normal electrical service is interrupted.

The branches of the emergency system shall be installed and connected to the alternate power source so that all functions specified for the emergency system shall be automatically restored to operation within 10 seconds of interruption of the normal source.

General considerations. Essential electrical systems for hospitals must consist of an emergency system and an equipment system. The emergency system only consists of circuits essential to life safety and critical patient care. The equipment system is dedicated to major electrical equipment necessary for patient care and basic hospital operation.

The number of transfer switches to be used shall be based on reliability, design, and load considerations. Each branch of the emergency system and each equipment system shall have one or more transfer switches. One transfer switch shall be permitted to serve one or more branches or systems in a facility with a maximum demand on the essential electrical system of 150kVA.

Other loads served by the generating equipment not specifically named in Art. 517 shall be served by their own transfer switches. These loads shall not be transferred if the transfer will overload the generating equipment. In addition, these loads shall be automatically shed upon generating equipment overloading. Hospital power sources and alternate power sources shall be permitted to serve the essential electrical systems of contiguous or same-site facilities. [NFPA 99, 3.4.2.2.1, 12.3.3.2].

On the wiring front, it's critical that you keep the life safety branch and critical branch circuits of the emergency system entirely independent of all other wiring and equipment. Don't place them in the same raceways, boxes, or cabinets with each other or other wiring (Photo on page 79). This rule is very similar to those found in 700.9(B) for emergency systems.

When installing isolated power systems in critical care areas that use anesthetizing gases, you must power task illumination fixtures, selected receptacles, and fixed equipment via an individual circuit that serves no other load. You must limit the number of receptacles placed on a single branch circuit for the items mentioned above to limit the effects of a branch circuit outage. Branch-circuit overcurrent devices shall be made readily accessible to nursing and other authorized personnel.

You must mechanically protect the wiring of the emergency system of a hospital by placing it in nonflexible metal raceways or using Type MI cable. These requirements don't apply to flexible power cords of appliances or other utilization equipment connected to the emergency system or secondary circuits of transformer-powered communications or signaling systems. The Code does allow for a few exceptions. For instance, you can use Schedule 80 rigid nonmetallic conduit for circuits that don't serve patient care areas. You can also use Schedule 40 nonmetallic conduit and electrical nonmetallic conduit, where encased in no less than 2 inches of concrete, to serve these same areas. You can also install flexible metal raceways and cable assemblies where it's necessary to provide for a flexible connection to equipment.

If a receptacle is supplied from the emergency system, it or its cover plate shall have a distinctive color or marking to be readily identifiable. If color is used to identify these receptacles, make sure you use the same one throughout the facility. Red is commonly used for this application. However, orange has been used in some facilities where red was selected for use on the fire alarm circuits.

In general, the components of the essential electrical system, with the exception of the alternate source of supply and transfer switches, are the same as those in the normal distribution system.

The equipment system. The equipment system primarily feeds power equipment, including central vacuum and medical gas equipment; pumps, control systems, and alarms required to operate for the safety of essential apparatus; heating equipment for specific designated areas; service for one elevator; supply and exhaust ventilating system for specific areas; and various other selected equipment. The equipment system is arranged so it's connected to the alternate source of power at appropriate time-lag intervals, as described in the Code.

In the case where a hospital has more than one elevator, a manual throw over switch should be installed so that each elevator can be bought to a floor, emptied of passengers, and power transferred to another elevator for the same purpose. After all passengers are removed, all but one elevator will be out of service. Under these circumstances the generator needs to be sized only for one elevator.

The emergency system. Those functions of patient care that depend on lighting or appliances connected to the emergency system shall be divided into two mandatory branches: the life safety branch and the critical branch.

The life safety branch of the emergency system shall supply power for the following lighting, receptacles, and equipment:

  • Illumination of means of egress
  • Exit signs
  • Alarm and alerting systems
  • Communications systems
  • Generator set location
  • Elevators
  • Automatic doors

No function other than those listed in 517.32(A) through (G) shall be connected to the life safety branch.

The critical branch shall supply power for task illumination, fixed equipment, selected receptacles, and special power circuits that serve the following areas and functions related to patient care:

  • Task illumination, selected receptacles, and fixed equipment in critical care areas that use anesthetizing gases

  • Isolated power systems in special environments

  • Task illumination and selected receptacles in patient care areas

  • Additional specialized patient care task illumination and receptacles, where needed

  • Nurse call systems

  • Blood, bone, and tissue banks

  • Telephone equipment rooms and closets

  • Task illumination, selected receptacles, and selected power circuits for general care beds (at least one duplex receptacle per patient bedroom), angiographic labs, cardiac catheterization labs, coronary care units, hemodialysis rooms or areas, emergency room treatment areas (selected), human physiolgenerating unit(s) located on the premises, or an external utility service when the normal source consists of a generating unit(s) located on the premises.

The equipment system shall be installed and connected to the alternate power source such that the equipment can be automatically restored to operation at appropriate time-lag intervals following the energizing of the emergency system [517.34(A)] or manually restored to operation [NFPA 99, 3.4.2.2.3(b)].

Equipment that must be arranged for delayed automatic connection to the alternate power source includes the following:

  • Central suction systems that serve medical and surgical functions, including controls

  • Sump pumps and other equipment required to operate for the safety of a major apparatus, including associated control systems and alarms

  • Compressed air systems that serve medical and surgical functions, including controls

  • Stair pressurization and smoke control systems, or both

  • Kitchen hood supply and exhaust systems or both, if required to operate during a fire in or under the hood [NFPA 99, 3.4.2.2.3(d)]

Equipment that must be arranged for either delayed automatic or manual connection to the alternate power source includes the following:

  • Heating equipment that provides heating for operating, delivery, labor, recovery, intensive care, coronary care, nurseries, infection/isolation rooms, emergency treatment spaces, and general patient rooms and pressure maintenance (jockey or make-up) pump(s) for water-based fire protection systems

  • An elevator(s) selected to provide service to patient, surgical, obstetrical, and ground floors during interruption of normal power

  • Supply, return, and ventilating systems for airborne infectious/isolation rooms, protective environment rooms, exhaust and for laboratory fume hoods, nuclear medicine areas where radioactive material if used, ethylene oxide evacuation, and anesthesia evacuation

  • Hyperbaric facilities

  • Hypobaric facilities

  • Automatically operated doors

  • Minimal electrically heated autoclaving equipment shall be permitted to be arranged for either automatic or manual connection to the alternate source

  • Controls for equipment listed in 517.34

  • Other selected equipment shall be permitted to be served by the equipment system [NFPA 99, 3.4.2.2.3(e)]

The engine-generator set should be equipped with provisions for automatic shutdown, including visible and audible indications (both local and remote) for conditions like low lubricating-oil temperature, high jacket-water temperature, over-speed, or failure to start. An ammeter and voltmeter, each with a phase-selector switch, should also be part of the generator set, together with a frequency meter and means of adjusting output voltage and frequency.

The rules of 700.7 require you to provide audible and visual signals to indicate derangement of the emergency source, the battery is carrying load, the battery charger isn't functioning, and a ground fault has occurred in a solidly grounded wye emergency system of more than 150V to ground and circuit-protective devices rated 1,000A or more.

The sensor for the ground-fault signal devices shall be located at, or ahead of, the main system disconnecting means for the emergency source, and the maximum setting of the signal devices shall be for a ground-fault current of 1,200A. Instruction on the course of action to be taken in the event of indicated ground fault shall be located at or near the sensor locations.

Transfer switches. The rating of the transfer switches shall be adequate for switching all classes of loads to be served and for withstanding the effects of available fault currents without contact welding. Each automatic transfer switch shall be approved for emergency electrical service as a complete assembly.

The transfer switch shall transfer and retransfer the load automatically. Non-automatic transfer switching devices shall be mechanically held. Operation shall be by direct manual or electrical remote manual control. Electrically operated switches shall derive their control power from the source to which the load is being transferred. A means for safe manual operation shall be provided.

Bypass-isolation switches shall be permitted for bypassing and isolating the transfer switch.

Conclusion. Don't forget to regularly provide maintenance for the essential electrical systems. You must test generator sets and transfer switches under load and operating temperature conditions at least once every 30 days. Permanently record all available instrument readings during the monthly test. Also pay particular attention to your fuel or gas systems, engine cooling system, engine lubricating system, engine electrical starting system, engine compressed air starting system, engine exhaust systems, and transfer switches.

General maintenance includes checking for any unusual condition of vibration, deterioration, leakage, or high surface temperatures or noise. Ensure that maintenance manuals, service logs, basic service tools, jumpers, and supplies are readily available. Check and record the time intervals of the various increments of the automatic start-up and shutdown sequences. Check overall cleanliness of the room. And ensure that there are no unnecessary items in the room.

Editor's note: The references from NFPA 70 National Electrical Code — 2002 Edition displayed as example [NFPA 99, 3.4.2.2.1] are based on the NFPA 99 Standard for Health Care Facilities - 1999 Edition.

Owen is the owner and president of National Code Seminars in Pelham, Ala.