Spec’ing hospital electrical distribution systems When specifying electrical distribution systems in hospitals, the engineer must account for the facility’s size, flexibility needs, emergency power needs, and safety requirements. BY NEAL BOOTHE, PE, exp US Services Inc., Maitland, Fla. Learning objectives Understand which codes govern the design of hospital electrical systems Learn the differences between emergency and essential power Learn and understand the unique electrical system requirements of hospitals. O n the surface, the electrical distribution system of a hospital may look the same as that for other types of buildings—offices, hotels, etc.— but there are several important distinctions. These distinctions are not so much in the equipment used. Panelboards, switchboards, transformers, circuit breakers, and other products are all common to other types of projects. The differences Figure 1: The University of California San Diego Jacobs Medical Center is a 10-story, 509,000-sq-ft building scheduled to open in 2016. Initially, it will have 161 beds, including 24 intermediate care unit beds, 24 bone marrow transplant beds, and 24 intensive care unit beds. exp US Services was responsible for the electrical design. Courtesy: UC San Diego Health System, Paul Turang, Photographer 22 Consulting-Specifying Engineer • MARCH 2013 lie primarily in the size and complexity of the electrical systems: the overall size of the electrical system, its need for a higher level of flexibility, enhanced needs for more emergency power that can remain operational for longer durations, and the need for enhanced safety in the hospital environment. Size does matter First, the electrical demands of a hospital far outweigh those for most other building types. One reason is that hospitals have unique equipment with very large power requirements, such as magnetic resonance imaging (MRIs), computer tomography (CT) scanners, and other imaging equipment. Second, even some equipment common to all buildings is larger for hospitals due to their complexities. A good example of this lies in air conditioning and ventilation systems, which can be two or three times larger in hospitals than in other buildings of a similar size due to the heightened air change rate, more stringent temperature requirements, and higher equipment loads. Also, many specialized areas in a hospital have a large number of receptacles to allow for a multitude of equipment to be used. For example, a hospital operating room may be 500 to 600 sq ft and include 30 or more receptacles due to the amount of equipment required in this space. An office building may have 10 receptacles www.csemag.com Normal power source Alternate power source Normal supply or less in a comparably sized area. Hospital lighting also follows the same thinking and typically has a higher lumen and Watts/sq ft requirement based upon the complex procedures (surgeries, examinations, and other medical procedures) that are performed. Similarly, the hospital’s emergency system will be significantly larger than that of other building types. Where all buildings require emergency power to help occupants safely exit in the event of normal power failure, hospitals also require emergency power to sustain the life of patients (who often are not capable of self-preservation due to illness or injury), and this emergency power is needed indefinitely (not just long enough to allow the public to safely exit the building). This requires a more robust and larger emergency power system. For example, a 200,000-sq-ft office building might require 50 to 100 kW of generator capacity to provide the emergency power it needs, whereas a 200,000-sq-ft hospital may need 2,500 kW or more of generator capacity. Another consideration becomes the need for sufficient fuel storage to sustain the emergency generators. For most buildings, fuel storage (usually diesel for generators) requirements are quite small. For a hospital, however, the dual considerations of much larger generators that need to run for longer time periods lead to very large on-site fuel storage needs. It’s not unusual to see a hospital with 30,000 gal or more of diesel fuel storage for its emergency generators. Emergency versus essential power Often the term “emergency” power is used to refer to all power needed on a generator in a hospital. A better term for this would be “essential” power. True, emergency power comprises only those loads required to be restored within 10 seconds as required by NFPA 70: National Electrical Code (NEC) Article 700 for all buildings, and as defined as life safety branch and critical branch by NEC Article 517 for hospitals. For a hospital, you have the essential power supply, which would www.csemag.com include the generator(s), and this power is divided into emergency system power and equipment system power. Then the emergency system is divided into the life safety branch and critical branch (of the emergency power system, as shown in Figure 2). The size, complexity, and needs for emergency power in a hospital are only a few of the ways in which its power distribution system differs from that of other building types. Nonessential loads Equipment system Automatic switching equipment Life safety branch Critical branch Essential electrical system Figure 2: NFPA 70-2011 Article 517 outlines the way in which the emergency system is divided into the life safety branch and critical branch. Courtesy: NFPA NEC Article 517: Articles 700 and 701 on steroids As mentioned, NEC Article 517 is dedicated to health care facilities. It should be noted that NFPA 99: Health Care Facilities Code also has specific electrical requirements for hospitals, but as these requirements are very close to those in NEC Article 517, we will focus on these NEC requirements. One other code that affects generator design and installation is NFPA 110: Standard for Emergency and Standby Power Systems. This code is more specific to generator installation requirements (and not the emergency loads that must be connected to them) for the most part, but includes many other important requirements for generators. NEC Articles 700 (Emergency Systems) and 701 (Legally Required Standby Systems) apply to all facilities (including hospitals); however, the requirements of Article 517 are typically more stringent and apply only to hospitals and other similar type health care facilities (nursing homes, ambulatory surgical centers, etc.). For both Articles 700 and 517, emergency power must be restored within 10 seconds of loss of normal power. NEC Article 700 requires that a portion of the building’s electrical system be capable of providing emergency power in the event of normal power failure. This would include features such as exit/egress lighting, fire alarm systems, and other similar life safety functions. This can be done via a small generator (for larger buildings) or battery backup power. This amount of power is typically a very small portion of the building’s total power consumption, about 5% to 10%. NEC Article 517 also requires that hospitals be provided with emergency power. Again, as hospitals must remain open throughout normal power interruption and include patients who rely on emergency power for preservation of life, this article divides the emergency branch (same terminology as Article 700) into two branches: the life safety branch and the critical branch (new terminology just for hospitals). In a hospital, the life safety branch of the emergency power system is very similar to the Article 700 requirement for other building types. It includes only the small amount of power necessary to allow for the safe evacuation of the public from the building in the event of normal power failure. This includes the exit/egress lighting and fire alarm systems—similar to other buildings—as well as other loads unique to the health care environment, such as medical gas alarm systems. It also includes generator set accessories loads (such as battery chargers and block heaters) that are necessary to ensure proper starting and operation of the generator. Again, these loads would include a very small percentage of a hospital’s total electrical system, typically 5% to 10% at most. Consulting-Specifying Engineer • MARCH 2013 23 All these requirements for critical branch power further increase the size of a hospital emergency power system. on. Article 517 requires even more available power in general and also more emergency power for these types of spaces. All these requirements for critical branch power further increase the size of a hospital emergency power system. Where life safety power would only be 5% of the building’s power requirement, the critical power system Figure 3: Two 1250 kW generators paralleled at the Cleveof a hospital could easland Clinic in Weston, Fla. Note the size of these generaily account for 25% or tors; the step ladder is needed to allow staff to review more of a hospital’s total the annunciator panel on the rear of the generator in the power requirement. foreground. Courtesy: Cleveland Clinic In addition to “true” As we’ve discussed, unique to the hos- emergency power, other power needs pital environment is the need to maintain in a building are also very important in patient safety during the loss of utility the event of normal power failure but power. This is where the second branch not necessarily needed for the preservaof the emergency system, the critical tion of life. This might include heating branch, takes over. The hospital’s criti- and refrigeration systems, ventilation cal branch is a much larger part of the and smoke removal systems, sewage electrical distribution system and handles disposal, industrial processes, and othloads such as much of the lighting and ers whose interruption could create a receptacles in patient rooms, intensive hazardous condition or hamper rescue care rooms, operating rooms, post-anes- or fire-fighting operations. For all buildthesia care units (PACUs), nurse stations, ings, this is covered by NEC Article 701: pharmacies, labs, blood banks, and other Legally Required Standby Systems, and similar types of spaces where patients these systems must be restored to power are either directly cared for or services within 60 seconds from loss of normal for these patients are arranged. Further, power. For a hospital, Article 517 further Article 517 identifies two different types defines these systems and calls them the of patient care areas—general care and equipment system. Article 701 doesn’t specifically define critical care—depending on the severity of the patient’s needs. A general care area which systems must be considered legally includes rooms such as a “normal” patient required standby but rather states that room or exam room where critical branch this designation should be made by the power is needed but the patient’s condi- designer and/or authorities having juristion is not severe. A critical care area then diction (AHJ). As there are so many difis exactly how it sounds: an area where ferent types of buildings with different the patient’s care is more dependent on hazards, the designer and code reviewthe hospital staff (and their need for more ers must use discretion. However, for a equipment and more emergency power). hospital, these equipment systems are This includes operating rooms, labor/ much better defined. They include large delivery rooms, intensive care units, medical gas suction systems, elevators, trauma areas in emergency rooms, and so kitchen hood supply/exhaust, ventilation 24 Consulting-Specifying Engineer • MARCH 2013 systems (supply/return and exhaust) for patient care areas, heating for patient care areas, large sterilizers, and similar type loads. Again, the equipment system of a hospital can be a substantial part of the overall electrical system, especially as much of this system is the larger equipment loads such as elevators, large air handlers, and sterilizers. The equipment system can easily account for 30% or more of the overall hospital electrical system. Even this equipment system power is further delineated based on the importance of the loads being served—into nondelayed automatic, delayed automatic, and delayed automatic or manual connection. These distinctions can require a minimum of three automatic transfer switches (ATS) for the equipment system. The highest equipment system level is the nondelayed automatic connection and includes only loads such as certain generator accessories. These loads (as the name suggests) must be automatically restored without delay upon loss of utility power (similar to emergency power). Note that these types of systems also may be connected to the life safety branch. (This would be a designer’s choice and may depend largely on the size and complexity 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: Legrand www.csemag.com of these systems.) Next, equipment such as medical air vacuum pumps and compressors, smoke control systems, ventilation systems for operating and labor/ delivery rooms, smoke control systems, and kitchen supply and exhaust systems must be automatically restored upon loss of utility power but are allowed to delay the emergency system restoration (typically under 1-minute delay). The final step of equipment power is allowed to have a delayed automatic connection (which would lag all other ATS) or even a manual connection to the generator system. This includes loads such as elevators, heating to patient care areas, automatic doors, sterilizing equipment, hyperbaric or hypobaric facilities, and other selected loads. In summary, the total amount of emergency power for most buildings (and therefore the amount of emergency distribution equipment needed) is typically 10% or less and consists of only that minimal amount of power needed to help people safely exit a building within the first few minutes of normal power interruption. For hospitals, emergency power becomes the life blood of a building without utility power and must be maintained throughout a power outage, which could last for days after a storm or other catastrophic event. As a result, it’s not unusual to see the emergency power of a hospital exceed 50% or 60% of the building’s total power needs. Also, as separate transfer switches are need for each type of load (life safety, critical, nondelayed automatic equipment, delayed automatic equipment, and delayed automatic or manual connection equipment loads), multiple ATSs are always needed for hospitals. For a 200,000-sq-ft hospital, eight or more transfer switches could be used. A similarly sized office building would typically have only two ATSs. 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, www.csemag.com GFP GFP GFP GFP / 800 3 GFP / 4000 3 GFP Switchboard ‘MSB’ 4000A BUS 480Y/277V, 3o, 4W GFP Utility transformer and hospital grade. Many of these designations have been developed by Other Other Other Other Other manufacturers to define loads loads loads loads loads the level of quality of these receptacles. TypiPanel ‘CDP’ 800/3 800A BUS cally, a residential grade 480Y/277V, 3o, 4W is lower quality than a commercial grade, 250/3 a commercial grade is lower quality than a specification grade, and Panel Other Other Other so on. The highest level ‘HA’ loads loads loads of quality for receptacles 20/1 Other is hospital grade. Hospiloads tal grade receptacles are manufactured to the highest standards to ensure Figure 5: This sample one-line diagram for a hospital grounding reliability, shows the coordination among the arrangement of the assembly integrity, over- 4000 A, 800 A, 250 A, and 20 A circuit breakers, such that all strength, and durabil- the lowest breaker should always trip first to prevent ity. All patient care areas electrical failure to other loads within the system. in a hospital are required Courtesy: exp US Services Inc. to use hospital grade receptacles per NEC Article 517. Further, receptacles in a hospital (such as at the it requires that hospital grade receptacles generator set location or by the automatic shall be marked to identify them as such. transfer switches). U.S. manufacturers typically mark a green dot on the front of the receptacle Grounding is twice as important (see Figure 4). Grounding is an issue that is often However, hospital grade receptacles misunderstood when discussing electriare not required throughout a hospital; cal distribution systems, and it’s not the they are required only in patient care intent of this article to define or explain areas (such as operating rooms, intensive grounding in-depth. From a simplistic care unit rooms, patient rooms, emergen- point of view, the grounding of an eleccy department exam rooms, labor/deliv- trical system is needed for many reasons ery rooms, etc.). They are not required in such as establishing the voltage reference offices, nurse stations, labs, pharmacies, point and enhancing the safety of the or other areas in the hospital, but they are electrical system by providing a return commonly used in all rooms of a hospital path for stray voltage/current in the systo provide the highest quality of recep- tem (and therefore keeping it away from tacles with the longest life and durability. you). For most buildings, every branch A different color (typically red) is circuit (defined as the last wiring from marked on emergency receptacles with- any panel or other source to the final in the hospital to help identify that these point of use) must be grounded. For the receptacles are on emergency power purpose of illustration, think of branch and will continue to operate during util- circuit wiring as the wire just behind the ity power outages. This is required by electrical receptacle or connected to the NEC Article 517 in critical care patient light fixture in your house or office. It areas but historically has been provided is the wiring that touches the electrical in all areas of the hospital for critical devices you touch. Poor grounding at this receptacles and even the few life safety level can lead to the possibility of you Consulting-Specifying Engineer • MARCH 2013 25 Another code requirement that adds significant complexity to the design of electrical systems is that of overcurrent coordination of the emergency system. Typically, only nonflexible being shocked when plugging metallic conduit is allowed in (or unplugging) your radio, in patient care areas due to phone, or other equipment. the need to provide redundant Furthermore, even though grounding and protection of the all ground buses in every panel branch circuit. There are a few should theoretically be at the exceptions; the NEC does allow same reference point (or zero flexible conduit for specific voltage point), there is always applications where nonflexible the possibility of very slight metallic conduit is not possible voltage differences between due to the need for flexibility. multiple panels grounding refThere is even a specific flexierence. As a result, NEC Article ble “health care grade” ac cable 517 requires that any panels that manufactured just for hospitals serve the same patient area must (where the flexible metal jacket have another grounding jumper is still rated as a grounding path (wire) connect their ground and a separate grounding conbuses to eliminate the possibilductor is installed within) for ity of even the smallest trace of these applications. any stray voltage that could be introduced to a patient. This is another requirement distinct to Breaker coordination the hospital environment. Another code requirement There are two acceptable that adds significant complexity means for providing groundto the design of hospital electriing for branch circuit wiring cal systems is that of overcurrent per NEC. One is by the use coordination of the emergency of a dedicated grounding wire Figure 6: This time-current curve illustrates coordination system. This requirement is actubeing run with the other wires among the breakers in a hospital electrical system. Any ally found in NEC 700, which in the circuit (the famous green overlap between breakers would indicate a possible applies to all building types. or sometimes bare wire any occurrence where a downstream breaker might trip before However, as mentioned previamateur electrician knows). an upstream breaker. Courtesy: exp US Services Inc. ously, the emergency system for The second method is the use most buildings is a very simple of metallic boxes and metallic conduits referred to as redundant grounding. This one concerned primarily with small loads throughout the branch circuit that are further enhances the safety of the electri- such as lighting, fire alarm, and other rated to provide an effective ground path cal system for the patient and staff. similar loads. In a hospital, the amount of back to the electrical source. emergency power and the larger size of Anyone who has ever been shocked Protection of the emergency system the distribution equipment needed further by an electrical appliance (meaning that Another requirement for hospitals in complicate this issue, as close to half (or stray voltage used them as a ground- NEC 517 is the need to provide mechani- more) of the panels and breakers in a large ing path instead of a grounding wire or cal protection of the emergency system hospital may be connected to life safety conduit system) can tell you that it is no (this would apply to life safety and criti- and critical branch power. The need to fun. Unfortunately, these incidents can cal branch power). This code greatly provide overcurrent coordination requires sometimes lead to injury or even death, reduces the available methods for the much more design attention to ensure that depending on other conditions. Obvi- wiring and conduit systems of emergen- downstream breakers will open (trip) prior ously, these concerns are greatly mag- cy power branch circuits. In non-patient- to larger upstream breakers so that any disnified for someone who is already in a care areas (where redundant grounding is ruption of emergency power is minimized. weakened state due to illness or injury. not required), methods include mineral Although this may seem simple enough, As a result, NEC Article 517 requires that insulated cable (very expensive, fire rated the tolerances of breakers is such that all branch circuits serving patient care cabling), PVC Schedule 80 conduit, or often larger electrical distribution equipareas must have both types of ground- conduits such as PVC Schedule 40 and ment is needed to provide coordination ing installed (grounding wire and the use some flexible metal conduits where than may be required based on the loads of metal raceway throughout)—often installed in 2 in. of concrete. being served. This further increases the 26 Consulting-Specifying Engineer • MARCH 2013 www.csemag.com cost of the electrical system and may also affect the physical size of the equipment. See Figure 5 for a sample overcurrent coordination curve on a hospital project. This figure shows four breakers that properly coordinate such that in each case the smaller breaker will trip before the larger breaker upstream of it. Graphically this is represented by the fact that none of these breaker curvesoverlap. This starts with the lowest level breaker on the left, with each level of distribution shown coordinating with the distribution level above and below. If any of these breakers were to overlap, it would indicate that at a certain current (on the horizontal axis) and time (on the vertical axis) either breaker could trip first. Ground fault protection Ground fault protection (GFP) is the sensing of current on an electrical system to ensure that there is not a dangerous ground fault occurring downstream in the electrical system. By comparing outgoing current (on the phase conductors) with neutral currents (the “return” current), GFP devices can determine if any current is being lost in the system (i.e., a fault condition). If this is the case, the GFP protection will open a breaker (typically the main breaker) and interrupt power to the system. The NEC requires GFP on the system’s main circuit breaker for solidly grounded systems of 1,000 A or more with a line-to-ground voltage of 150 V or more. As most electrical services in US buildings of sufficient size are 480 V line-to-line (which equals 277 V line-toground) and 1,000 A or more, this GFP is often required. For a hospital, however, NEC Article 517 expands the GFP provisions and requires two levels of GFP protection. So in a hospital, if an electrical service needs GFP due to voltage and size of the system, the main breaker and all the feeder breakers in the electrical service must be protected by GFP. This serves to enhance reliability by removing only one feeder (through which the fault is www.csemag.com travelling) instead of removing power from the whole service (by tripping the main breaker for the system). Similar to overcurrent coordination, this is another case where the code recognizes the need to isolate an electrical condition in a hospital electrical system in order to minimize any power disruption. Electrical systems unique to hospitals Although most electrical equipment in hospitals is common to other building types, there are some systems unique to hospitals—notably, isolated power systems. Originally introduced in hospitals due to the use of flammable anesthetics (commonly ether) many years ago, these systems were once mandatory in all areas where anesthesia was used. Flammable anesthesia hasn’t been used in hospitals for many years, but isolated power systems remain for some applications. NEC Article 517 requires the use of isolated power systems in “wet” locations where power disruption cannot be tolerated. The NEC code leaves the determination of wet locations to the hospital’s discretion, but areas commonly considered to be wet include some general surgeries, open heart surgery, orthopedic surgeries, and cystoscopy. Please note that the 2012 edition of NFPA 99 recently included in its requirements that all operating rooms are identified as wet locations unless a risk assessment has been provided to ensure that fluids within the space will cause no danger to patient or staff (Section 6.3.2.2.8.4). As a result of this revision, the use of these complex electrical panels will likely increase significantly in future hospital projects. Isolated power systems serve to reduce the risks of electric shock hazards from patients’ or staff members’ inadvertent contact with stray voltage and allow for the safe continuation of electrical appliance use in the event of a low-level fault condition where loss of power could affect patient safety. These systems are also designed to limit the leakage of electrical current in the system (which is very small but common in any electrical system) that may cause an electrical shock. Though such a shock is normally very small and poses little risk of harm, it becomes magnified in a wet location or with a patient more susceptible to any contact to even very minor stray voltage (such as a patient in a heart surgery where any voltage introduced to the heart could have fatal consequences). Further, these systems are capable of monitoring even these smallest amounts of leakage current (under 5 mA, or five one-thousandths of an amp) and providing alarms of dangerous levels of leakage current. As you may imagine, the use of these complex electrical systems in a hospital adds significant costs and maintenance issues. The only constant is change Most buildings experience some level of change throughout the years—offices are renovated, finishes are updated, etc.— but in a hospital this level of change in the building’s functions is much more frequent and can be more drastic. Anyone who lives or works at or near a hospital can tell you that construction seems to be ongoing. As new technologies and treatments come and go, the building’s infrastructure changes frequently. As a result, hospital electrical systems must be designed with extra flexibility and spare capacity to help accommodate the inevitable changes. This, coupled with the fact that the hospital electrical distribution system is a much larger and more complex system than that of other building types, means hospital electrical systems must be designed to be more robust. Neal Boothe, PE, is a principal and electrical engineer at exp, where he specializes in the design of hospital electrical systems. He has more than 18 years of experience, including over 200 projects ranging from new, greenfield hospitals to additions and renovations of existing facilities. Read the longer version of this online at: www.csemag.com/archives. Consulting-Specifying Engineer • MARCH 2013 27