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How many equipment grounding conductors (paths) are required to be installed for a branch circuit supplying patient care areas when the governing body of the healthcare facility specifies isolated grounding (IG) receptacles for specific medical equipment? This question comes up far too often in the field to be left without a thorough explanation.
The short answer is three equipment grounding conductor paths are necessary for this circuit to meet the minimum requirements in the National Electrical Code (NEC).
General safety of persons and property
Electrical wiring installations have to be adequate to meet the intentions of design parameters and must always meet the minimum requirements of the applicable electrical code. Electrical contractors and workers are trained to understand and adhere to the safety rules contained in the NEC. This is an inherent part of doing business in the electrical wiring profession.
The NEC places strong emphasis on wiring and protection in Chapter 2 with a host of rules addressing equipment grounding and bonding. To the seasoned veteran electrical worker, installing branch circuits is a routine task in any electrical project. Each branch circuit generally is required to be equipped with a safety circuit, the equipment grounding conductor. No big revelation so far, but let’s suppose the branch circuit is installed in an area where patient care is administered, such as a hospital treatment room. The rules change. They change to become more restrictive.
Contractors working in healthcare facilities have to be familiar with the more restrictive NEC rules for branch circuit wiring in patient care areas. After all, this is their business. This article reviews some important NEC rules related to branch circuit equipment grounding in patient care areas of healthcare facilities. More specifically, it reviews designs that specify isolated grounding receptacles and circuits in patient care areas.
Review of 90.3
Understanding the arrangement of the NEC is an important element of installing electrical wiring that satisfies the rules and is safe. Section 90.3 of the NEC provides a basic road map of the Code regarding arrangement and clearly indicates how the rules are to be applied. Electrical contractors and electricians are typically most familiar with the general requirements contained in Chapters 1 – 4 of the document. A closer look at 90.3 reveals that Chapter 5 of the NEC can modify or supplement the general rules in Chapters 1 – 4 (see figure 1).
The subjects covered in this article involve installations in which the general rules in NEC chapters 1 – 4 are applicable and amended to become more restrictive to address additional safety concerns for patients in healthcare facilities. When isolated grounding receptacles and circuits are specified for patient care locations, the minimum required safety circuits must not be compromised to maintain conformity with the NEC.
Isolated grounding receptacles in designs
Enhanced equipment grounding circuits for information technology equipment and isolated grounding receptacles are design criteria (desired) and specification that is not a requirement of the NEC, but safety requirements are provided for such specified installations. It is important to understand from a functional standpoint that the required equipment grounding conductors of branch circuits must not be affected by the installation of isolated equipment grounding conductors for IG receptacles. A good approach is to think of the isolated equipment grounding conductor, often referred to as a clean ground, as one in addition to the required equipment grounding conductor of the branch circuit, not in place of it.
Reducing electrical noise in the grounding circuit
The whole purpose of specifying and installing an isolated equipment grounding conductor for an IG receptacle circuit is to provide an insulated equipment grounding path that provides a level of insulation (isolation) from varying degrees of electromagnetic interference (EMI) on the grounding circuit. Installing an isolated insulated equipment grounding conductor provides an insulated conductive path (wire conductor) that is connected to the point of grounding connection either at the service equipment or at the source of a separately derived system. This insulated conductor connects to the isolated insulated grounding terminal of an IG receptacle that is isolated from grounded metal parts at the outlet. This creates the isolation effect and reduction of electrical noise on the equipment grounding circuit, other than capacitance and magnetic coupling effects.
Safety grounds and clean grounds
The NEC does not use the terms clean ground or safety (dirty) ground (See figure 2). These terms often are used in the information technology industry to differentiate between the normal equipment grounding conductor (safety ground) of a branch circuit and the isolated equipment grounding conductor (clean or quiet ground).
Isolated grounding receptacles often are installed in information technology rooms containing sophisticated electronic equipment that is sensitive to electrical noise (electromagnetic interference) on the grounding circuits.The reference to safety ground (dirty ground) used in IT jargon is related to the required equipment grounding conductor as defined in Article 100 of the Code. When dealing with NEC requirements, it is always important to use the words and terms that are defined by the particular industry standard. This promotes accuracy in their application and understandability. For the purposes of this article, the Code terms are used to support the concept of proper application of NEC rules to installations and systems. The following is a collection of Code-defined terms included in this article.
Bonded (Bonding)—Connected to establish electrical continuity and conductivity.
Branch Circuit—The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s).
Conductor, Insulated—A conductor encased within material of composition and thickness that is recognized by this Code as electrical insulation.
Grounded (Grounding)—Connected (connecting) to ground or to a conductive body that extends the ground connection.
Grounding Conductor, Equipment (EGC)—The conductive path installed to connect normally non–current-carrying metal parts of equipment together and to the system grounded conductor or to the grounding electrode conductor, or both.
FPN No. 1: It is recognized that the equipment grounding conductor also performs bonding.
FPN No. 2: See 250.118 for a list of acceptable equipment grounding conductors.
Receptacle—A receptacle is a contact device installed at the outlet for the connection of an attachment plug. A single receptacle is a single contact device with no other contact device on the same yoke. A multiple receptacle is two or more contact devices on the same yoke.
Functional concepts of equipment grounding
Safety has to be first, always.
The purpose of the NEC is the practical safeguarding of persons and property from the hazards arising from the use of electricity [90.1(A)]. The NEC includes the minimum requirements, which means one must do at least that much for electrical wiring to be essentially safe and free from hazards to persons or property. Installing equipment grounding conductors with branch circuits is required for safety. The required equipment grounding conductor (safety circuit) must never be eliminated when installing isolated insulated equipment grounding conductor for an isolated grounding receptacle outlet. It is a serious mistake to install isolated insulated equipment grounding conductors from IG receptacles and connect them directly and only to a grounding electrode such as a water pipe of building steel or an auxiliary grounding electrode such as a ground rod. This violates the performance requirements for grounding and bonding set forth in Section 250.4(A) of the Code. Remember that the term isolated grounding conductors does not mean the safety grounding circuit or the isolated insulated grounding circuit is isolated or floating from the original point of grounding on the system. Installing isolated equipment grounding conductors for IG receptacles requires a safety grounding circuit and a clean grounding circuit that satisfy the requirements in 250.4(A)(5) and provide an effective ground-fault current path. Section 250.6 addresses objectionable current in the grounding circuits and offers remedial solutions to problems arising from objectionable current on the grounding conductors. It should be noted that Section 250.6(D) is clear to prohibit equipment from being operated on a circuit that is not connected to an equipment grounding conductor (safety ground).
Functions of equipment grounding conductors
In general, equipment is required to be grounded. This is accomplished by installing equipment grounding conductors with branch circuits (See Figure 3). Equipment grounding conductors perform three essential functions when properly installed. First they serve to ground equipment by providing an electrical connection from the equipment to a grounding electrode. Equipment grounding conductors also perform bonding functions as indicated in the definition of the term. The equipment grounding conductor also provides an effective ground-fault current path for the branch circuit. This path must carry fault current to facilitate overcurrent device operation, thus protecting the circuit, equipment and persons.
Branch circuits for receptacles in patient care areas
Now that we’ve reviewed the basic principles of equipment grounding for safety and NEC requirements for equipment grounding conductors, let’s take a look some strengthened equipment grounding requirements for special occupancies, specifically health care facilities. Wiring and protection rules for health care facilities are provided in Part II of Article 517. Section 517.13 deals with equipment grounding conductors for branch circuits serving patient care areas and requires compliance with both subdivisions (A) and (B) with that section.
Two equipment grounding conductor paths required
To simplify this requirement, subdivision (A) requires a metal raceway system or metallic armor or sheath of a cable assembly that qualifies as an equipment grounding conductor in accordance with 250.118. Subdivision (B) requires the branch circuit also include an insulated copper equipment grounding conductor sized according to 250.122 (See Figure 4). So as one can see by these rules, two separate equipment grounding conductor paths are required for branch circuits serving patient care areas. These circuits can be installed using metallic raceway wiring methods that meet the requirements for equipment grounding conductors or by installing listed metallic cable assemblies that include a metallic sheath or armor that meets the equipment grounding conductor criteria as provided in 250.118. Note that the two paths required by this rule have to be different in characteristics. In other words, two insulated equipment grounding conductors pulled through a PVC conduit does not meet the minimum requirements of this section.
Redundancy of equipment grounding circuit
The objective here is to install two separate equipment grounding conductor paths to always be assured to have one way of building redundancy in the safety circuitry for patient care locations or not having all our eggs in one basket. The basic reasons are to ensure effective safety grounding of receptacles and fixed equipment within patient care locations and the facilitation of overcurrent protective device operation during ground fault events.
Branch circuits for IG receptacles in patient care areas
What if the specifications call for an isolated grounding receptacle for the branch circuit serving a patient care location? Photo 4 shows a patient care location where isolated grounding receptacles are specified for computer and medical equipment in that location.
The Code does not require the isolated insulated equipment grounding conductor, but it does address installations where it is installed by choice or as desired. In these situations the branch circuit simply ends up with three separate equipment grounding conductors. Two equipment grounding conductor paths are installed to satisfy 517.13(A) and (B) and the third is installed and connected to the insulated grounding terminal of the isolated grounding receptacle (See Figure 5).
The NEC indicates that where isolated receptacles are installed for reducing electromagnetic interference on the grounding circuit, a receptacle in which the grounding terminal is insulated from the device mount strap (yoke) is permitted. The receptacle is permitted to be connected to an insulated equipment grounding conductor can pass through one or more panelboards without a connection to the panelboard grounding terminal bar as permitted in 408.40, Exception, so as to terminate within the same building or structure directly at an equipment grounding conductor terminal of the applicable derived system or service [NEC 250.146(D)]. It is important to understand that the isolated insulated equipment grounding conductor for the IG circuit does not count as one of the required equipment grounding conductor paths referred to in 517.13(A) and (B). The isolated insulated equipment grounding conductor is over and above the required equipment grounding conductors with the branch circuit serving the patient care area (See Figure 5). The reason the IG conductor cannot be considered as meeting the requirements in 517.13(A) and (B) is because it does not benefit functionally from the other parallel equipment grounding conductor paths. The isolated insulated equipment grounding conductor is not connected to the safety equipment grounding conductor at both ends of the circuit, just one. It is isolated and insulated from grounded metal parts at the receptacle end. See Section 517.16 and the fine print note for additional information.
The electrical industry is experiencing high volume of work in the health care facility construction. Electrical contractors should be in tune to all the NEC requirements that apply to wiring installations in patient care locations. The rules in Chapter 5 of the NEC, specifically Article 517 often modify the general requirements in Chapters 1 – 4 and usually more restrictive fashion. Branch circuits serving patient care locations are required to provide two equipment grounding conductor paths according to Section 517.13(A) and (B). When a design calls for an isolated grounding receptacle and circuit to be installed in a patient care area, the branch circuit must not only meet the requirements for two equipment grounding conductors as called for in 517.13, but must include a third insulated equipment grounding conductor that meets the rules in 250.146(D) and 406.2(D). Where isolated grounding receptacles are installed in patient care areas, three equipment grounding conductors must be installed to satisfy the requirements branch circuit equipment grounding and specifications calling for additional isolated insulated equipment grounding conductors and receptacle for reducing electrical noise (electromagnetic interference) on the grounding circuit.
JOHNSTON, former director of education, codes and standards for IAEI, is NECA's executive director of standards and safety. he is a member of the IBEW and an active member of the NFPA Electrical Section, Education Section and the UL Electrical Council. Reach him at [email protected].
About The Author
JOHNSTON is NECA’s executive director of codes and standards. He is a member of the NEC Correlating Committee, NFPA Standards Council, IBEW, UL Electrical Council and NFPA’s Electrical Section. Reach him at [email protected].