Redundantly grounding all electrical equipment in a patient care area has provided one of the most critical pieces of a very complex puzzle involving patient protection. A careful study of the issues surrounding grounding in these areas will provide the installer with a better understanding of redundant grounding and the ultimate goal of providing an equipotential plane surrounding the patient.
Section 517.13 provides information and requirements for redundant grounding, the text and the FPN in Section 517.11 provide the explanation for establishing and maintaining an equipotential plane around the patient care area. An equipotential plane, as applied to a patient care area, establishes an area surrounding the patient in which metal objects, the patient, all personnel within reach of a patient, and all electrical equipment are at the same electrical potential or zero difference of potential between any point within the patient care area.
A patient care area is defined in Section 517.2 as “any portion of a health care facility wherein patients are intended to be examined or treated.” These areas within the health care facility are where the patient will most likely come into contact with electro-medical devices through external or internal connection to or through the patient’s skin. A patient care area can be either general care or critical care areas, and either a general care area or a critical area can involve a wet (procedure) location.
A wet procedure location in a patient care area is a location that is normally subject to wet conditions while a patient is present. These locations usually involve some type of wet procedure with standing fluids on the floor or drenching of the work area, either of which is intimate to the patient or staff. Routine housekeeping procedures and incidental spillage of liquids are not considered to be a wet (procedure) location since a medical procedure is not involved. An example of a wet procedure would involve a patient being immersed in water while still connected to electro-medical devices, such as would be the case with hypothermia cases or similar applications. In wet (procedure) locations, creating and maintaining an equipotential plane is critical since very small differences of potential can have serious consequences for the patient.
Patient vicinities are spaces where electrical devices have metal surfaces likely to be contacted by the patient or an attendant who can touch the patient. Typically in a patient room, this encloses a space within the room not less than 1.8m (6 feet) beyond the perimeter of the bed in its nominal location, and extending vertically not less than 2.3m (71/2 feet) above the floor. Again, maintaining an equipotential plane is critical in this area since even small differences of potential can cause current flow that can have devastating affects on the patient, especially where the patient is connected internally to the electrical equipment.
Section 517.11 provides information via the Fine Print Note that preventing a conductive or capacitive path from the patient’s body to a grounded object in close proximity to the patient is very difficult. The path of current through the patient’s body to a grounded object may be accidental or it may be through electrical equipment actually connected to the patient. As the number of electrical devices and apparatus that are near or connected to the patient increase, the hazard of current flow, through the patient to other grounded surfaces or from one electrical device, also increases.
Control of the electrical shock hazard to the patient involves controlling the amount of electrical current that may flow from the electrical equipment through the patient to some grounded object or to another piece of electrical equipment. This control can be accomplished by raising the resistance of the circuit (including the patient) or by insulating exposed surfaces that might become energized or that could develop a difference of potential to another adjacent surface. When two metal surfaces or two different medical devices develop a difference of potential, a natural capacitance is formed (commonly called distributed capacitance) with air being the dielectric between the two different plates of the capacitor. Even this relatively small capacitive discharge from one surface to another through medical devices connected to a patient by external leads can have catastrophic effects on the patient.
Section 517.13 requires a redundant grounding path be established by using a separate insulated equipment grounding conductor in conjunction with a totally separate grounding path on either a metal raceway or a cable with an outer metal armor or metal sheath identified as an acceptable grounding return path. Requiring all branch circuits for fixed electrical equipment and receptacles supplying power to equipment in the patient care area to have a redundant grounding system ensures a positive grounding path and helps establish the equipotential plane surrounding the patient. EC
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 email@example.com.