Specifying Hospital Electrical Distribution Systems

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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
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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
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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
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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
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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,
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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
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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
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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
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