My August 2007 article, “Isolated Ground Receptacles,” questions whether isolated ground (IG) receptacles should be permitted in a patient care area. I wrote that Article 517 of the National Electrical Code (NEC) applies to electrical construction and installation criteria in healthcare facilities, providing healthcare services to human beings. Part II of Article 517 provides the requirements for wiring and protection in a healthcare facility and is applicable to patient care areas for all healthcare facilities.

This was somewhat misleading, since there is at least one section within Part II that should not have been used in a patient care area. Section 517.16 in Part II applied to receptacles with insulated-grounding terminals and permitted these IG receptacles in a general or critical patient care area. The last sentence of my August 2007 article states that 517.16 should be clarified for the 2011 NEC, since the text in that section in the 2008 and previous Codes appeared to permit IG receptacles in a patient care area to be supplied by branch circuits that were not in compliance with 517.13(A) and (B).

Section 517.13(A) and (B) requires two grounding methods for branch circuits supplying power to receptacles and fixed equipment within a patient care area. The first method of grounding requires all branch circuits serving patient care areas to be provided with an effective ground-fault current path by installation in a metal raceway system or a cable having a metallic armor or sheath assembly. The metal raceway system, metallic cable armor or sheath assembly must qualify as an equipment-grounding conductor in accordance with 250.118.

The second method for grounding requires the grounding terminals of all receptacles and all noncurrent-carrying conductive surfaces of fixed electrical equipment that are likely to become energized—which are subject to personal contact and operating at more than 100 volts—to be connected to an insulated copper equipment-grounding conductor. The two separate equipment-grounding systems for receptacles or fixed equipment in a patient care area ensures that, if one grounding system is lost, there is always a backup grounding system to maintain the equipotential plane surrounding the patient.

Panel 15 accepted Proposal 15-29 in the 2010 Report on Proposals to make the following text changes for 517.16 in the 2011 NEC: “517.16 Receptacles with Insulated Grounding Terminals. Receptacles with insulated grounding terminals, as described in 250.146(D), shall not be permitted.” The new text clearly states that IG receptacles are not permitted in a patient care area, and the fine print note has been deleted.

There were two comments, Nos. 15-41 and 15-42, submitted to reject this proposed change to 517.16. The substantiation in Comment 15-41 was: “Accepting this proposal removes provisions for installing isolated grounding receptacles and IG circuits without technical substantiation. Chapter 4 of NFPA 99 [the current edition and the proposed revised standard] still includes provisions and requirements for IG circuits and receptacles (quiet grounds) installed in healthcare facilities. Medical equipment and appliance manufacturers continue to produce equipment that recommends use of isolated ground receptacles and circuits in their installation instructions. Electrical device manufacturers continue to produce hospital-grade IG receptacles for use in patient care areas when required according to design and performance specifications and engineered plans.”

The substantiation in Comment 15-42 was: “The reduction of electrical noise provided by Isolated Ground receptacles may be critical to the proper operation of sensitive medical instrumentation. If the installation of IG receptacles were to be prohibited, the result may be the additional hazard to patient safety introduced by the possible malfunctioning of sensitive medical instrumentation due to electrical noise. The proposal substantiation is based on the FPN stating that caution must be used when installing IG receptacles. As noted in the NEC Handbook, Section 517.16 is intended to prevent indiscriminate use of IG receptacles in patient care areas. The FPN expresses the need for caution when installing IG receptacles in patient-care areas. Due to construction features of the IG receptacle that isolate the receptacle grounding terminal from the receptacle strap caution must be exercised when installing IG receptacles where redundant grounding is required by 517.13. The proposed connection of two insulated grounding conductors to an IG receptacle provides the redundant grounding scheme required by 517.13.”

The panel’s response was to continue accepting the proposal and reject the comments as stated: “The panel agrees with the substantiation brought forth in Proposal 15-29. The panel contends that one cannot have a redundant ground system and at the same time adequately maintain an isolated ground system. The panel further contends that patient safety should take precedence over noise reduction.”


ODE is a staff engineering associate at Underwriters Laboratories Inc., based in Peoria, Ariz. He can be reached at 919.949.2576 and mark.c.ode@us.ul.com.