Spec’ing hospital electrical distribution systems

03/18/2013


All receptacles are not created equal

Many different types of electrical receptacles are available today. Common types are general use, residential grade, commercial grade, specification grade, and hospital grade. Many of these designations have been developed by manufacturers to define the level of quality of these receptacles. Typically, a residential grade is lower quality than a commercial grade, a commercial grade is lower quality than a specification grade, and so on. The highest level of quality for receptacles is hospital grade. Hospital grade receptacles are manufactured to the highest standards to ensure grounding reliability, assembly integrity, overall strength, and durability. All patient care areas in a hospital are required to use hospital grade receptacles per NEC Article 517. Further, it requires that hospital grade receptacles shall be marked to identify them as such. U.S. manufacturers typically mark a green dot on the front of the receptacle (see Figure 4).

Figure 4: A red and an ivory hospital grade receptacle are shown. Note the green dot on each to indicate that these are hospital grade. Red receptacles typically indicate emergency power connections. Courtesy: LegrandHowever, hospital grade receptacles are not required throughout a hospital; they are required only in patient care areas (such as operating rooms, intensive care unit rooms, patient rooms, emergency department exam rooms, labor/delivery rooms, etc.). They are not required in offices, nurse stations, labs, pharmacies, or other areas in the hospital, but they are commonly used in all rooms of a hospital to provide the highest quality of receptacles with the longest life and durability.

A different color (typically red) is marked on emergency receptacles within the hospital to help identify that these receptacles are on emergency power and will continue to operate during utility power outages. This is required by NEC Article 517 in critical care patient areas but historically has been provided in all areas of the hospital for critical receptacles and even the few life safety receptacles in a hospital (such as at the generator set location or by the automatic transfer switches).

Grounding is twice as important

Grounding is an issue that is often misunderstood when discussing electrical distribution systems, and it’s not the intent of this article to define or explain grounding in-depth. From a simplistic point of view, the grounding of an electrical system is needed for many reasons such as establishing the voltage reference point and enhancing the safety of the electrical system by providing a return path for stray voltage/current in the system (and therefore keeping it away from you). For most buildings, every branch circuit (defined as the last wiring from any panel or other source to the final point of use) must be grounded. For the purpose of illustration, think of branch circuit wiring as the wire just behind the electrical receptacle or connected to the light fixture in your house or office. It is the wiring that touches the electrical devices you touch. Poor grounding at this level can lead to the possibility of you being shocked when plugging in (or unplugging) your radio, phone, or other equipment.

Furthermore, even though all ground buses in every panel should theoretically be at the same reference point (or zero voltage point), there is always the possibility of very slight voltage differences between multiple panels grounding reference. As a result, NEC Article 517 requires that any panels that serve the same patient area must have another grounding jumper (wire) connect their ground buses to eliminate the possibility of even the smallest trace of any stray voltage that could be introduced to a patient. This is another requirement distinct to the hospital environment.

There are two acceptable means for providing grounding for branch circuit wiring per NEC. One is by the use of a dedicated grounding wire being run with the other wires in the circuit (the famous green or sometimes bare wire any amateur electrician knows). The second method is the use of metallic boxes and metallic conduits throughout the branch circuit that are rated to provide an effective ground path back to the electrical source.

Anyone who has ever been shocked by an electrical appliance (meaning that stray voltage used them as a grounding path instead of a grounding wire or conduit system) can tell you that it is no fun. Unfortunately, these incidents can sometimes lead to injury or even death, depending on other conditions. Obviously, these concerns are greatly magnified for someone who is already in a weakened state due to illness or injury. As a result, NEC Article 517 requires that all branch circuits serving patient care areas must have both types of grounding installed (grounding wire and the use of metal raceway throughout)—often referred to as redundant grounding. This further enhances the safety of the electrical system for the patient (and the hospital staff).

Protection of the emergency system

Another requirement for hospitals in NEC 517 is the need to provide mechanical protection of the emergency system (this would apply to life safety and critical branch power). This code greatly reduces the available methods for the wiring and conduit systems of emergency power branch circuits. In non-patient-care areas (where redundant grounding is not required), methods include mineral insulated cable (very expensive, fire rated cabling), PVC Schedule 80 conduit, or conduits such as PVC Schedule 40 and some flexible metal conduits where installed in 2 in. of concrete.

Typically, only nonflexible metallic conduit is allowed in patient care areas due to the need to provide redundant grounding and protection of the branch circuit. There are a few exceptions; the NEC does allow flexible conduit for specific applications where nonflexible metallic conduit is not possible due to the need for flexibility. There is even a specific flexible “health care grade” ac cable manufactured just for hospitals (where the flexible metal jacket is still rated as a grounding path and a separate grounding conductor is installed within) for these applications.



BRIAN , UT, United States, 03/21/13 04:36 AM:

This article leaves much to be desired regarding hospital electrical systems. The graphic shown is only applicable for a tiny building covered under NEC 517, or smaller than 150kVA...in accordance with 517.30 B 4. I hope this isn't included in the printed version.
JITAO , NY, United States, 03/21/13 09:08 AM:

Should the three essential branches be fed from three separate ATS's?
Anonymous , 03/22/13 03:57 PM:

Some States even require bypass transfer switches.
PHILIP , PA, United States, 03/22/13 07:53 PM:

How are non-linear loads being addressed and what sizing changing were made to accomodate them?
SPENCE , VA, United States, 03/28/13 08:33 AM:

This article appears to be a broad brush to homogenize the design of hospital systems. But the author used a diagram that is applied only for small hospital facilities,typically less than 150 Kva of load. While the author aknowledged the extensive use of emergency power for various systems, he did not address the need clearer definitions for sizing the emergency systems. For instance, is a demand factor appropriate in the sizing of emergency systems?
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