Some of the most challenging electrical installations involve healthcare. From major hospitals to clinics in pharmacies, anyone who is not intimately familiar with the intricacies of medical headwalls, major electrical equipment (such as cardiac catheterization, CAT scans, MRIs) or even the mounting and supply of operating lights is in for a real lesson in humility.
This article covers grounding of branch circuits and feeders to ensure safe procedures that are necessary for the installation so the patients, nurses, doctors and all others in proximity will not be subject to spurious electrical currents and other similar hazards. Proper grounding and bonding are necessary for electrical safety in any healthcare area, but it is extremely important for patient-care areas, especially in general-care and critical-care environments.
The review of healthcare facilities starts by explaining the general construction criteria in 517.11 of the National Electrical Code and the accompanying informational note. This section states that the purpose of Article 517 is to specify the installation criteria and wiring methods that will minimize any electrical hazards in the healthcare facility. This is accomplished by the installation and maintenance of adequately low potential differences between exposed conductive surfaces that are likely to become energized and could be contacted by the patient. The informational note states that it is difficult to prevent the occurrence of a conductive or capacitive path from the patient’s body to some conductive object.
The issue for the patient area is that any difference of electrical potential between a patient and the electrical equipment could cause problems and adversely affect that patient and anyone working on that person. Let’s say there is a difference of potential between a piece of electrical equipment and a patient during open heart surgery. Even a small amount of capacitive difference of potential—with an accompanying small current discharge to the heart during the operation—could cause the patient’s heart to restart. The same amount of capacitive current discharge through the skin would not normally be an issue, but the same amount of current directly to the heart during the operation could be a major issue. In the case of surgery, a patient can be electrocuted at current levels that are extremely low. This can occur where any electrical device is exposed to any patient that is subject to an invasive procedure but is extremely critical where a heart catheter or similar application may occur. A small amount of current could be the difference between life and death.
Three methods can be used to control electric shock hazards, and they are discussed in the informational note to 517.11. The first is to raise the resistance of the conductive circuit to limit the amount of electrical current that might flow into the patient’s body from any source. This method of raising the resistance may amount to very high resistances, as may be found in the mega-ohm values, or may involve an ungrounded system where an isolation transformer is installed so that everything on the secondary side of the transformer is ungrounded. This would require an equipment grounding conductor be installed on the secondary side of an ungrounded transformer with a leakage sensor connected to the ungrounded conductors (in the case of a 120-volt circuit, the neutral conductor and the hot conductor are ungrounded) and the equipment grounding conductor to determine the amount of leakage current for each piece of electrical equipment in proximity of the patient. This system is covered in 517.20 for wet procedure locations and 517.160 of the NEC , which explains the requirements for establishing a monitored ungrounded system.
The second method is to insulate any exposed metal surfaces near the patient so there is little possibility of any unwanted current that could reach the patient from any electrical source.
The third method is a combination of the first two. The key issue here is providing protection for the patient to prevent any difference of electrical potential, thereby limiting any spurious current to as close to zero as possible and creating an equipotential zone. If there is zero difference of potential, then there will be no current flow.
If the patient can be enveloped in an equipotential plane, and there is no difference of potential anywhere in proximity, the patient and staff will be assured of a safe installation for any invasive procedure (any procedure that penetrates the protective surfaces of the patient’s body performed in an aseptic field). Whether the installation is new, a remodel or normal replacement during maintenance, adherence to the requirements in Article 517 is critical in maintaining safety.