Healthy Separation

Emergency circuits are installed in patient bed locations in general care and critical care areas in hospitals to ensure power is available to electrical equipment even where normal power is lost for some reason. Storms, equipment failure, brownouts and similar electrical system problems could cause loss of power to the hospital and ultimately could cause loss of power to the electrical equipment and critical loads at the patient bed location. Within 10 seconds of the loss of normal power, the emergency system generators in the hospital are required to start and supply power to any critical loads essential for the life safety of the occupants and to provide for “normal cessation of procedures.”

These requirements have been in the National Electrical Code (NEC) for many years and are necessary for the proper care of patients in hospitals. The issue is whether all emergency “critical branch” circuits should be installed together without regard to related requirements for separate transfer switches and panelboards where normal circuits are replaced with all critical branch circuits at general care or critical care patient bed locations.

Patient bed locations in general care areas and critical care areas in hospitals are required to have at least two branch circuits to each area, one or more from the normal system, and one or more from the emergency system. All normal system branch circuits in general care patient bed locations must originate in the same panel-board, and the same requirement exists in a critical care patient bed location.

Originating all the circuits in the same normal system panelboard permits easy access to all normal system circuits, so a circuit breaker may be reset where it has tripped due to overload, short circuit, or ground fault. These normal system branch circuits are not required to be identified in any special manner or have the receptacles marked with the panelboard and circuit number at the general care or critical care patient bed location.

In critical care patient bed locations, any emergency system receptacles or the receptacle covers must be identified by color or some other similar means in accordance with Section 517.30(E), and the receptacle must have the circuit number and panelboard identification on the receptacle in accordance with Section 517.19(A)’s last sentence. This marking should be readily visible and permanently applied on the receptacle (many installations provide this marking on the receptacle cover) to make it easy to locate the panelboard and circuit in an emergency situation where reset time may be critical.

Wherever possible, the circuit number and panelboard identification also should be applied under the receptacle plate on the yoke of the receptacle in case the receptacle covers are removed for painting or cleaning of the room, although this is not an additional requirement within the NEC. This application will ensure easy and proper identification of the circuits and panelboard for emergency receptacles where covers have been marked and then removed.

A new Exception No. 2 was added to Section 517.19(A) in the 1996 NEC, permitting critical care patient bed locations to be supplied from two separate transfer switches on the emergency system without any normal system power. In the 1999 NEC, a similar Exception No. 3 was added to Section 517.18(A) permitting two separate transfer switches and no normal system power for general care patient bed locations.

Each separate transfer switch would be connected on the load side to a panelboard supplying emergency power branch circuits to general care or critical care patient bed locations. Attention to detail ensures two separate transfer switches are installed to isolate the two emergency systems from each other and to minimize the possibility of total loss of power to the patient bed locations by a short circuit or ground fault affecting both emergency supply sources.

Section 517.30(C)(1) requires the life safety branch and the critical branch of the emergency system to be kept entirely independent of all other wiring and equipment and does not permit either branch to enter the same raceway, box or cabinet with normal wiring or with each other. Keeping each branch separated from all other wiring helps maintain the isolation from other systems and helps ensure that these other systems will not adversely affect the operation and integrity of these important systems. Section 517.30(C)(1)(4) permits two or more emergency circuits from the same branch to share the same raceway, box, cabinet or equipment. The permission to share raceways, boxes, cabinets or equipment as provided in Section 517.30(C)(1)(4) would seem to nullify the attempts to keep the two transfer switches and panelboards separate where normal circuits are not supplied to a general care or critical care patient bed location. Since the NEC usually mandates minimum requirements, designers, contractors and installers can accomplish separating these two emergency systems.

ODE is a staff engineering associate at Underwriters Laboratories Inc., in Research Triangle Park, N.C. He can be reached at 919.549.1726 or at

About the Author

Mark C. Ode

Fire/Life Safety Columnist 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 .

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