Power Quality For Healthcare Facilities

PQ TechWatch A product of the EPRI Power Quality Knowledge program

Power Quality for

Healthcare Facilities December 2007

Philip Keebler, EPRI

CONTENTS Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . .1 The Healthcare Environment . . . . . . . . . . . .1 Power Quality in Healthcare Facilities . . . . .3 Recognizing Power Quality Problems . . . . . .4 Symptoms and Their Causes . . . . . . . . . . . .4 Sources of Electrical Disturbances . . . . . . .8 Improving Power Quality in the Healthcare Environment . . . . . . . . . . . . . . . .13 Meeting the Power Quality Challenges of the Healthcare Industry . . . . . . . . . . . . .13 Establishing Partnerships . . . . . . . . . . . . . .13 Creating a Power Quality Checklist for Procuring Equipment . . . . . . . . . . . . . . . . .14 Using Power-Conditioning Devices to Improve Equipment Compatibility . . . . . . .16 Understanding Facility Voltage Requirements, Grounding, and Dedicated Circuits . . . . . . . . . . . . . . . . . . .17 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . .24 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . .24

EXECUTIVE SUMMARY

The healthcare environment is made up of perhaps the most unusual combination of electronic loads found in any facility. Healthcare facilities not only rely upon commercial loads (such as computers, servers, and lighting system) and industrial loads (such as food preparation equipment, laundry equipment, medical gas systems, but also rely on electronic medical loads (that is, medical equipment) to operate the facility and provide patient care services. As in other facilities, when an electrical disturbance such as a voltage sag, voltage transient, or voltage swell reaches the service entrance of the healthcare facility or medical location, computers in the accounting department may shut down, and motor starters and contactors providing power to the air-conditioning and ventilation system may change the environment within the facility. Unlike other places, however, a patient’s life could be threatened when an aortic balloon pump trips off-line during a cardiovascular surgery. The costs associated with downtime can be staggering, but no bounded cost can be placed on the irreversible result of loosing a patient. Building, electrical, and healthcare codes in the United States require that hospitals and other medical clinics have emergency power ready to activate upon the detection of a power quality problem and assume the load within 10 seconds of the detection. However, even though a generator may be used at a healthcare facility or medical location, it cannot be on-line to support critical medical equipment with an activated transfer switch in less than about 2 to 3 seconds at best. This duration of time might as well be forever in terms of the ability of electronic medical equipment to continue operating. In fact, an undervoltage as short as ¼ of a cycle (about 4 milliseconds) is often sufficient to confuse sensitive electronic devices. This PQ TechWatch will introduce the typical problems found in healthcare facilities, enlighten the reader on some new issues, and provide practical guidelines for avoiding those problems.

About the EPRI Power Quality Knowledge Program The EPRI Power Quality Knowledge program provides a wealth of resources in well-designed, readable, and accessible formats. Paramount among these resources are documents covering a wide range of PQ topics, written not only for use by busy PQ professionals, but also to be shared with important end-use customers and internal utility managers. The program’s website, www.mypq.net, is the most comprehensive electronic PQ resource available, providing 24-7 access to proven expertise via the PQ Hotline, hundreds of PQ case studies, over 200 PQ technical documents, PQ standards references, indexes, conference presentations, and a wealth of other resources. For more information, please visit www.mypq.net.

Copyright 2007, EPRI (www.epri.com). All rights reserved. Distribution of PQ TechWatch is subject to a license agreement with EPRI. No portion of this report may be reproduced or redistributed in any form, including electronic copies, without prior written consent from EPRI. Distribution outside the licensed organization is expressly forbidden. Product and company names mentioned in this document may be trademarks of their respective companies. Mention of third-party products is for informational purposes only and constitutes neither a recommendation nor an endorsement. EPRI and the EPRI logo are trademarks of EPRI.

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Power Quality for Healthcare Facilities

Healthcare providers have little time to be concerned with the quality of power or to find a reliable source of power to operate their equipment.

INTRODUCTION

Although the electricity provided to a healthcare facility or medical location is an absolute necessity for healthcare providers to operate their facilities, it is usually not given a lot of thought. The widespread growth of new and lingering illnesses and diseases, the call for increasingly critical emergency services, and the pressure to reduce healthcare costs force healthcare providers to keep their minds on their business—caring for their patients, enlisting the best possible healthcare professionals, and purchasing and installing the best medical equipment that money can buy. Turning on a heart-lung bypass machine prior to a six-hour openheart surgery where the operating room

problem to cripple the emergency medical staff. A second CT machine may not be an option, and the nearest machine may be many miles away in another hospital. This mission-critical imaging system could be taken off-line by a minor voltage sag to 80% of nominal (i.e., a 20% sag), lasting for only three 60-hertz cycles (50 milliseconds). The U.S. power quality community has estimated that $10 billion is lost yearly when automated control systems in industrial plants are upset by voltage sag events. Such numbers have not been estimated specifically for healthcare facilities or providers, but one can assume that the cost of downtime will also include possibly placing one or more patients at risk.

lights “are always on” has become as routine as activating a medical gas supply of oxygen

The Healthcare Environment

for a patient and then adjusting the flow rate

The healthcare environment in the United

so the patient receives the desired amount of

States is in continual transition in efforts to

oxygen. Healthcare providers have little time

improve patient care. Aside from the

to be concerned with the quality of power or

practice of medicine, nursing, and other

to find a reliable source of power to operate

medical-related fields, two areas key to the

their equipment. They need quality power 24

success of these transitions are (1)

hours per day, 365 days per year. Moreover,

improvements in the design, construction,

the time spent on power quality concerns is

and maintenance of healthcare facilities,

becoming shorter and shorter as bottom-line

and (2) the identification, selection,

pressures continue to be applied.

installation, and maintenance of medical equipment. Lessons learned in the area of

In most situations, instead of focusing on

power quality for healthcare demonstrate

the power quality, they have learned ways to

that efforts made beforehand to incorporate

“work around” malfunctioning and failed

power quality into these two areas usually

medical equipment. When one blood-

prevent significant interruptions in patient

pressure monitor is broken (possibly from a

care services and escalations in the costs of

voltage surge), a nurse or medical

medical equipment downtime.

technician goes and finds another monitor.

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But, in smaller healthcare facilities where

The healthcare environment encompasses

equipment may be limited, providers may

everything associated with patient care and

find themselves with fewer pieces of

the healthcare facility from the time the

redundant medical equipment and without

patient enters the facility to the time the

resources including power to operate the

patient leaves the facility. This environment

facility. To healthcare providers, the

includes healthcare functions that occur

malfunction or failure of one key piece of

outside and inside the facility. Healthcare

medical equipment—a computed

facility designers, planners, architects, and

tomography (CT) scanner in an emergency

engineers and facility operating engineers

room, for example—would be enough of a

and maintenance support personnel should

Power Quality for Healthcare Facilities

Healthcare staff can contribute to improving patient care and the environment through increasing their level of awareness in recognizing equipment malfunctions that may be caused by power quality problems.

focus upon those parts of the environment that contribute to shaping the quality of power and depend upon the quality of the

Complex Electronic Medical Equipment Used in Patient Care Areas

power in providing patient care. Healthcare staff, including medical professionals, can also contribute to improving patient care and the environment through increasing their level of awareness in recognizing equipment malfunctions that may be caused by power quality problems. New electrotechnologies are continually introduced into this complex environment (see figure on right), placing new challenges upon the healthcare and facility staff, the quality of power delivered to the facility and to the equipment, and the electricity demand. These electrotechnologies may also consume additional floor space and weight load and place new burdens upon the facility infrastructure—electrical and mechanical systems. These new technologies include medical, functional, and facility equipment. „ Examples of new medical

electrotechnologies include diagnostic imaging systems capable of

New technologies, such as electronic machines in the

resolving more patient detail,

intensive care unit (top) and those used for laparoscopic

computer-based wireless clinical

imaging (bottom), are continually being introduced into the healthcare environment.

information systems, and advanced patient diagnostic and therapeutic equipment. Additionally, much of the medical equipment is mobile,

Today, the public and the government are

requiring reliable, well-regulated

making unprecedented demands upon the

electricity on tap throughout a facility.

healthcare industry to provide high-quality,

„ Examples of new functional

technologies include microprocessor-

restructuring and mergers are just two

based food preparation equipment

examples of how the healthcare industry is

and laundry equipment that use

meeting a financial challenge that leaves

adjustable speed drives.

little room for equipment malfunction.

„ Examples of facility equipment

include energy management systems, electronic controls for facility HVAC systems and equipment, and medical gas systems.

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cost-effective patient care. Corporate

To ensure that the safe operation of medical equipment does not become a casualty of this new corporate mentality, the U.S. Congress passed the Safe Medical Device Act in 1990 (Public Law 101-69), which

Power Quality for Healthcare Facilities

For equipment with low immunity, electrical disturbances are a primary cause of damage and malfunctions.

establishes a partnership in safety between

Power Quality in Healthcare Facilities

the healthcare industry and manufacturers

Although inadequate and faulty wiring and

of medical equipment in the United States.

grounding systems and equipment interactions can exacerbate power quality

This act is required to track all implantable medical devices and life-supporting or lifesustaining devices listed in the act—such as

problems in healthcare facilities, electrical disturbances can damage low immunity

pacemakers, pulse generators, and

equipment or cause malfunction. In facilities

automatic defibrillators—that were distributed outside healthcare facilities after

where wiring and grounding systems are error free and equipment immunity is known,

August 29, 1993.

electrical disturbances are less likely to cause

The electrical environment in U.S.

power quality problems. Additional causes of power quality problems include the generation

National Electrical Code (NEC). The purpose

of disturbances from the normal operation of medical, functional, and facility equipment.

of this code is to provide minimum

For example, a contactor that controls power

standards to safeguard life or limb, health,

to part of the heating system in a facility can generate voltage transients that could impact

healthcare facilities is regulated by the

property, and public welfare by regulating and controlling the design, construction, installation, quality of materials, location, operation, and maintenance or use of electrical systems and equipment. This code regulates the design, construction, installation, alteration, repairs, relocation, replacement, addition to, use, or maintenance of electrical systems and

the operation and reliability of electronic medical equipment powered by the same panel that powers the heating system. In this situation, using a contactor that contains a snubber to limit the voltage transients and powering the heating system from a separate feeder circuit than the one powering the medical equipment will help resolve the problem.

equipment.

Microprocessor-Based Electronic Medical Equipment

Before the introduction of electronic medical equipment, common electrical disturbances were inconsequential to healthcare operations. Today, however, common electrical disturbances may cause high-tech medical equipment to malfunction, which is a problem given the intimate connection between this equipment and the patients that hospitals serve (see figure at left). Much of this equipment incorporates sensitive electronic power supplies and microprocessors (see figure on top of following page)—possibly resulting in extended patient discomfort, misdiagnoses, increased equipment downtime and service costs, and even life-threatening situations. Moreover, equipment damage and malfunctions can jeopardize patient safety and increase the cost of healthcare.

The healthcare environment is a unique one because of the intimate proximity of people to equipment.

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Power Quality for Healthcare Facilities

Medical equipment used in the United

Circuit Boards from a Medical Imaging System

States, such as diagnostic imaging systems, that present dynamic loads to the facility electrical systems can cause power quality problems internal to the facility. The figure at lower left is an example of a nonlinear current waveform captured by a power quality monitor connected to the input of a CT scanner during imaging system operation. From the figure, one can see that the current is very nonlinear and is characteristic of a high inrush current when the system is placed into the scan mode. If the healthcare facility contains wiring and ground errors with its earthing system, then

Integrated circuits, sensitive to electrical and electromagnetic disturbances, are used in electronic medical equipment.

Although patient safety is the number one reason for reducing the potential for equipment malfunctions, healthcare administrators must also consider the bottom line. Electrical disturbances can result in repeated diagnostic tests, wasted medical supplies, and expensive service and repair calls. These unexpected events are not covered by any healthcare insurance provider. The increasing use of healthcare insurance and the increased coverage limitations therefore compel healthcare facilities to minimize all equipment malfunctions.

Current (50 amps/division)

Non-linear (Harmonic-Rich) Load Current from a CT System

Time (10 milliseconds/division)

This medical imaging system creates dynamic power quality problems in healthcare facilities with wiring and grounding errors.

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dynamic loads such as those characteristic of diagnostic imaging system operation cause PQ disturbances that may impact other electronic devices in the hospital or even interfere with the operation of the dynamic load itself.

RECOGNIZING POWER QUALITY PROBLEMS

Symptoms and Their Causes Disturbances can enter healthcare equipment through any electrical port—the AC power input, telecommunications, or network—common in the facility’s electrical environment. Most disturbances will enter the AC power port and present themselves to equipment’s power distribution unit or power supply. Because most medical equipment in a healthcare facility is networked to other equipment, variations in the facility grounding system provide paths for disturbances to enter the equipment’s telecommunications and network ports. The effects of electrical disturbances upon healthcare equipment can be noticeable or unnoticeable. Disturbances entering AC power input, telecommunications, or network ports may not cause immediate damage to electrical and electronic components or cause equipment to fail suddenly. Depending upon the type of

Power Quality for Healthcare Facilities

The most common equipment malfunctions are caused by the inputs and outputs of microprocessors erroneously switching on and off because of voltage sags, swells, transients, andmomentary power interruptions.

disturbance—undervoltage or overvoltage, its duration, and the immunity of the equipment to that disturbance—gradual or fast occurring damage to electrical and electronic components may result. A disturbance such as a voltage surge entering the AC power input of medical equipment may not be sufficiently mitigated by internal overvoltage and overcurrent protection devices and may propagate through the power supply to other sensitive electronic subsystems and components. Voltage sags may cause post-sag inrush currents, which may cause permanent damage to overcurrent protection devices. A series of disturbances occurring over the period of a few hours or a few months, for example, may chip away at internal protection devices and electronic components, although damage to equipment may be virtually unnoticeable. Intermittent equipment malfunctions may be noticeable until eventual failure occurs. However, the most common equipment malfunctions are caused by the inputs and outputs of microprocessors switching between an on and off state resulting from voltage sags, voltage swells, voltage transients, and momentary power interruptions. For example, a voltage sag may cause the DC voltage (produced by the power supply) to the microprocessor of a blood-pressure monitor to decrease or suddenly change such that one or more of the microprocessor inputs or outputs drop from an on state to an off state. Or, a voltage transient incident upon the power supply may cause a change from an off state to an on state. In either case, data may be lost or scrambled, or the microprocessor may lock up or otherwise misoperate. Additionally, such changes in logical states can alter stored data, such as the control parameters of a defibrillator, ventilator, or an imaging system. Healthcare staffs have also reported power quality problems that are obviously not related to the malfunction of a microprocessor, such as 60-hertz artifacts on the signal recordings of biomedical equipment. The following are the most common symptoms of medical equipment

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malfunction, including malfunctions not related to microprocessors. Distortion of Displayed Medical Information

Medical information displayed on cathode ray tubes (CRTs), liquid crystal displays (LCDs), printouts, and film may be distorted by disturbed DC voltages powering the display, a microprocessor malfunction, or faulty data from memory. For example, a waveform from an electrocardiogram printout may be disfigured, film from an X-ray may have a hot spot (a white area without any detail), or a video display on a physiological monitor may be distorted. Faulty data from memory or a microprocessor may also degrade the quality or resolution of an image captured by an imaging system such as a CT scanner (see figure below). Caregivers who encounter distorted information often report that they had to repeat tests or were unable to make timely, critical decisions because of the distortion.

Distorted Computed Tomography Image and Digital Readout

Variations in DC voltages can cause problems with the images and digital readouts from CT scanners.

Power Quality for Healthcare Facilities

Electrical disturbances can cause microprocessor -based medical equipment to malfunction.

Incorrect Diagnostic Results

unacceptable levels of 60-hertz current), and

Electrical disturbances can alter the control

miswired or damaged equipment that forces

parameters stored in electronic medical

supply current through ground conductors.

equipment and used to diagnose a patient’s

Electromagnetic fields from certain electrical

condition. For example, the status of a CT

distribution equipment, medical equipment,

system may be misreported via the digital

and facility equipment can also produce stray

readout as illustrated in the figure on the

magnetic fields that can cause these artifacts.

previous page. Moreover, biomedical

Artifacts in medical data may also be caused by

equipment such as blood-pressure monitors

current flowing in conductors that are not

may display diagnostic data, such as a digital

contained in conduits.

readout or level indicator, that disagrees with the patient’s prevailing condition. Incorrect diagnostic results may also be caused by 60-hertz noise coupled to the patient or to the leads of diagnostic equipment such as electrocardiographs (EKGs) (see figure below) and electroencephalographs (EEGs). Such noise is commonly associated with stray currents caused by faulty grounds (i.e., miswired ground conductors carrying

Equipment Lockup

Electrical disturbances can cause microprocessor-based equipment to lock up and fail to capture data used by caregivers to make critical medical decisions. Infusion equipment used to administer a patient treatment may fail to regulate or count the proper dosage. The lockup of a medical imaging system wastes the valuable time of patients, imaging technicians, and medical staff and may extend patient discomfort

Incorrect Diagnostic Results

when imaging scans must be repeated. Moreover, lockups of life-support equipment such as defibrillators pose lifethreatening risks to patients. Rebooting of medical equipment may take as long as two hours and in some cases cannot be accomplished if equipment software becomes damaged from electrical and electromagnetic disturbances.

Procedure Interruptions

Electrical disturbances may lock up microprocessor-based medical equipment, resulting in interrupted medical procedures. The consequences of these interruptions range from minor inconveniences to patient jeopardy. For example, if the video system fails during a routine laparoscopic surgery, the surgeon may have to incise the patient An artifact-infested electrocardiograph (top) appears to match a textbook example of

to complete the operation, an unplanned

arrhythmia (bottom) (reproduced from Capuano, 1993). The waveform on the top had a

procedure that significantly increases the

rate of 300 beats per minute or 5 hertz and was accepted and diagnosed as arrhythmia,

patient risk, recovery time, and the cost of

or atrial flutter (but actually was not).

6

patient care.

Power Quality for Healthcare Facilities

An electrical disturbance can damage an electronic component or circuit board in medical equipment causing a loss of data stored in memory or even destroying the memory altogether.

Loss of Stored Data

Control or Alarm Malfunctions

An electrical disturbance can damage an

The possible results of microprocessor

electronic component or circuit board in

malfunction include the loss of equipment

medical equipment causing a loss of data

control (see figure below) or the false

stored in memory or rendering the memory

sounding of an alarm. For example, the

inaccessible. Such losses can occur in data

keypad on an infusion pump may not

stored in the memories of biomedical

respond to finger touches of medical staff,

equipment and imaging systems, as well as

the pump may not remain in the desired

billing and patient records stored in

programmed state, or the equipment may

computer memory. If previously stored data

sound an alarm contrary to the condition of

suddenly becomes unavailable as a result of

the equipment or patient. Moreover, if an

a disturbance incident upon an electronic

unstable patient condition develops and an

data storage system, then patient tests may

equipment alarm does not sound, then the

need to be repeated, delaying patient

patient may be placed in a life-threatening

treatment. Power supply, mainframe,

situation. Some medical devices such as

memory, interface, and other types of circuit

infusion pumps have a built-in battery

boards may suffer damage from

backup that provides for internal backup

disturbances. Permanent damage to a power

power in the event of a sag or momentary

supply circuit board, like that shown in the

interruption. The use of a backup battery

figure below, may initiate the loss of stored

system in a medical device does not protect

data on a circuit board downstream of the

the device from malfunctions caused by

power supply board.

voltage transients and other disturbances.

Damage to a Power Supply Board

Nurse Checking on the Status of a Patient after Resetting a Medical Device

False alarms or, worse, alarm failures may result from any instrument malfunction, presenting a possible risk to patients and increased workload for healthcare professionals. A temporary overvoltage permanently damaged this power supply board from a medical instrument.

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Power Quality for Healthcare Facilities

Equipment malfunctions can be avoided if the level of power quality is known and equipment selected or installed to be immune.

Sources of Electrical Disturbances

Faulty Facility Wiring and Grounding

The most common causes of electrical

In a fair number of cases, the cause of a

disturbances that lead to power quality

power quality problem in healthcare

problems in healthcare facilities and

facilities and medical clinics is simply a

medical clinics are

loose or corroded power or ground connection. Many medical equipment

„ low and unknown equipment

immunity; „ faulty facility wiring and grounding;

malfunctions attributed to poor power quality are caused by inadequate electrical wiring and grounding. Such problems frequently arise when

„ facility and equipment

modifications; „ high-wattage equipment; „ routine electric utility activities; „ accidents, weather, and animals; and „ a transfer to an emergency generator

or alternate feeder.

„ new electronic medical or office

equipment is connected to existing facility wiring; „ permanently installed medical

equipment is moved from one location to another; or „ underlying non-PQ-related

equipment malfunctions are not Low and Unknown Equipment Immunity

The immunity of most electronic medical equipment to electrical disturbances is low, unknown, or both. This is evidenced by the

resolved and changes to wiring and grounding are made in efforts to “enhance” the quality of power to the equipment.

number of cases of medical equipment malfunction and damage that are caused by

Wiring and grounding errors also enhance

power quality problems. Many power quality

the negative effects of neutral-to-ground

problems can be avoided if the quality of

transients, which disrupt electronic medical

power is known at the point of use within

equipment. Reversal of neutral and ground

the healthcare facility and if equipment

conductors; poor, missing, or redundant

immunity is known and high enough to

neutral-to-ground bonds; and poor, missing,

avoid equipment malfunction. When

or redundant equipment grounds are a few

immunity is unknown, healthcare providers

examples of faulty wiring and grounding

cannot determine if disturbances are likely

that can lead to medical equipment

to cause equipment malfunction and

malfunctions.

damage. As a result, healthcare providers cannot provide the utility with the data they

Many facility engineers and electricians in

need to warrant improvements to the power

healthcare facilities in the United States

system and cannot determine the degree of

used to mistakenly believe that if electrical

mitigation that can be provided by

systems are wired and grounded according

improving the operation of facility electrical

to Article 517 of the NEC (National Fire

systems (that is, identifying wiring and

Protection Association [NFPA] 70), there

grounding errors and resolving them) and by

should be no problems with the equipment.

utilizing power quality mitigation

By increasing the level of awareness of the

equipment.

impacts of power quality and compatibility on healthcare facilities and medical equipment through EPRI research, facility

8

Power Quality for Healthcare Facilities

The power supply equipment and wiring in a healthcare facility may fully comply with applicable standards, codes, and recommended practices and still be inadequate to prevent interruption of sensitive electronic equipment.

engineers, facility designers, and maintenance directors are realizing the importance of the integrity of their electrical

Power-Factor Correction Capacitors at a Substation Near a Healthcare Facility

systems in shaping the quality of power used for patient care. However, Article 517 focuses on electrical construction and installation criteria in healthcare facilities to reduce the risk of electrical shock and fire; it does not address power quality in the facility. The standard NFPA 99 entitled Handbook for Healthcare Facilities, also commonly used in the United States, focuses on the installation and performance of equipment in a healthcare facility, but also does not address power quality. The equipment and wiring in a healthcare

Switching capacitors in and out of service can create

facility may fully comply with applicable

transients that impact sensitive instrument.

standards, codes, and recommended practices and still be inadequate to support sensitive electronic equipment commonly found in a healthcare facility. (MRI) systems, CT scanners, and linear accelerators operate at high line voltages, Routine Electric Utility Activities

require high steady-state current, and

To correct the power factor of electricity,

present dynamic loading (see figure on

electric utilities routinely switch large

following page) to healthcare facility power

capacitors (see figure on top right) onto the

systems. During startup, this type of

power lines. These switching activities may

equipment draws very high inrush current—

generate transient overvoltages, called

as high as 70 times the normal operating

“capacitor-switching transients,” which may

current—which can cause voltage sags and

enter a healthcare facility or medical

other electrical disturbances on adjacent

location at the service entrance. These types

circuits not properly sized for these loads.

of electrical disturbances are more likely to

Problems occur when the circuits connected

occur in the morning and evening, when

to such disturbance-causing equipment

industrial facilities are powering up and

were not carefully planned for high-wattage

down. Other routine activities such as the

equipment. Such problems most often arise

operation of reclosures and breakers that

after a facility has recently undergone a

occur to maintain and stabilize the power

renovation or expansion or has recently

system and reduce the effects of electrical

moved existing medical equipment or

disturbances caused by natural events (e.g.,

installed new medical equipment. Also,

lightning) can result in some residual

installing high-wattage electronic

disturbances.

equipment without upgrading the existing facility power system (i.e., switchgear,

High-Wattage Medical Equipment with

transformers, and electrical wiring and

Dynamic Load

grounding) to accommodate the higher power consumption may result in overload,

9

Large medical equipment such as X-ray

undervoltage, and even overvoltage

machines, magnetic-resonance imaging

conditions.

Power Quality for Healthcare Facilities

Harmonic-Rich Current from an MRI System

facilities and medical clinics may find that equipment malfunctions are more prevalent on windy days when tree limbs may contact

Current (20 amps/division)

power lines. Voltage sags and interruptions may also be caused by lightning strikes, animals climbing atop the electrodes of a transformer or other utility equipment, and power-line conductor and insulator failures.

Downed Power Pole Adjacent to a Healthcare Facility

Time (25 milliseconds/division)

This distorted current waveform was captured with a power quality monitor during a PQ field investigation at a healthcare facility.

Voltage sags originating from outside a facility can be caused by downed, crossed, and contacted power lines.

Mechanical equipment containing loads that are inductive (e.g., motors) and resistive (e.g., heating elements)—such as heating, ventilation, air-conditioning, transportation, refrigeration, and pump equipment, which are controlled by starters and contactors—may also create electrical disturbances. The startup, normal operation, and shutdown of this equipment can cause voltage sags, transient overvoltages, and electrical noise.

Accidents, Weather, and Animals

Voltage sags originating from outside a

This toppled power pole caused a power outage at the

facility—which may account for more

healthcare facility nearby.

increased patient risk than any other single

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type of disturbance—can be caused by

Facility electrical modifications

downed (like that shown in the figure on the

Renovating and annexing healthcare

right), crossed, and contacted power lines

facilities and medical clinics are common in

and are most likely to occur during

the global modern healthcare industry, as

inclement weather conditions and peak

are the addition of transformers, subpanels,

demand times. Cars crashing into utility

and circuits to an electrical system and the

poles and ice-laden, wind-blown, or

use of temporary circuits to power existing

overgrown limbs touching and landing on

equipment. The rerouting of feeder and

power lines may create a path from the

branch circuits can result in the

power line to ground, creating electrical

commingling of loads (powering sensitive

disturbances and power interruptions for

electronic medical equipment from the

some and voltage sags for many. Healthcare

same bus as disturbance-generating loads). Power Quality for Healthcare Facilities

To provide power to some construction

manual transfer switch. (Ideally, in facility

equipment, temporary electrical circuits

electrical designs where provisions for a

may be connected to the wiring of existing

second utility feed are included, the second

structures, or construction equipment may

feed should come from a different

be connected to the output of motor-

substation, but this is not always possible.)

generator sets. The operation of

If the transfer switch is not properly

construction equipment such as arc welders

installed, adjusted, and maintained to

(see figure below) and line-powered

ensure a smooth transfer of power, the

motorized rotary equipment on the center’s

transfer may produce electrical disturbances

wiring system may introduce electrical

that are severe enough to cause malfunction

disturbances into branch circuits powering

of electronic medical equipment. Inspection

sensitive electronic medical equipment.

of generator wiring (see figure below) will reveal important wiring and grounding characteristics that are vital to the

Construction of a Shielded Room for an MRI Suite Using an Arc Welder

emergency power system. Engineers in healthcare facilities and medical clinics may also find that malfunction and damage to medical equipment may occur during routine generator testing (if generator testing is required by local, state, and international codes and laws). Most master generator control centers include an adjustable time delay to ensure that the generators are placed online or offline without creating electrical disturbances.

Searching for a Neutral-to-Ground Bond in the Emergency Generator at a Healthcare Facility Arc welders can introduce electrical disturbances into the branch circuits on which medical equipment are operating.

Transfer to and from Emergency Generator or Alternate Feeder

To ensure that power is always provided to feeder circuits that power subpanels and branch circuits connected to critical-care equipment, some electrical codes require that healthcare facilities have ready access to emergency power. Whether the source of emergency power is an on-site generator or a second utility feed, transferring from the normal power source to the emergency source is accomplished with an automatic or

11

Generator wiring should be inspected and maintained to avoid producing electrical disturbances during a power transfer.

Power Quality for Healthcare Facilities

So You Think You Need Uninterruptible Power Supplies? In healthcare facilities where power quality

installation and maintenance of these

the facility. These devices are designed to

problems occur frequently, healthcare

systems, even when new large medical

operate on internal batteries, and thus

providers may be eager to purchase and

equipment is specified and purchased. Large

continuous operation of this equipment is

install power quality mitigation equipment to

medical equipment such as diagnostic

possible during a voltage sag or momentary

protect both small and large loads from

imaging systems can be fitted with a UPS at

interruption. One should note, however, that

electrical disturbances. In situations where

the installation site, but the barriers in doing so

electronic medical equipment with an onboard

small loads such as biomedical equipment do

are significant. Imaging suites are tight on

battery recharger and an internal rechargeable

not contain internal battery backup systems,

floor space, and the electrical system provided

battery may also malfunction during an electrical

installing an appropriately sized uninterruptible

for these spaces was not designed to

disturbance as the charger could be rendered

power supply (UPS) will increase the

accommodate the installation of power

inoperable as a result of a deep voltage sag;

immunity of these loads to common

mitigation equipment. Moreover, imaging

hence the need for characterizing this equipment

disturbances such as sags and momentary

system operators do not have time to routinely

for immunity to sags and interruptions.

interruptions. UPSs for large medical loads

test a UPS or maintain the UPS’s batteries. Even though electric utilities try to provide as

ranging from 10 kVA to a few hundred kilovoltamperes, which can cost as much as $1 million,

Unlike industrial and manufacturing facility

many nines of reliable power to a healthcare

may be installed on an individual medical

environments where industrial process

facility as possible, healthcare providers must

imaging system, can support multiple systems

systems can be made much more robust to

realize that their facilities are also fed from

in a medical imaging department, or can be

voltage sag phenomenon with proper

typical power distribution networks. Utilities

used for a group of critical equipment such as

electrical and software design techniques,

will make every effort to ensure that a direct

ventilators in an intensive care unit (ICU).

most medical equipment is not designed to

service feed (service entrance) to a hospital is

offer this option. Medical equipment is

properly maintained and that second feeds are

In many situations where large UPSs are

designed for individual use in an array of

provided from a second substation whenever

thought to be needed (and some are needed),

equipment and for compact use. For example,

possible. However, redesigning distribution

healthcare providers discover that common

the ten different types of medical equipment

systems or making other investments in the

disturbances are exacerbated by typical wiring

used in an ICU are not linked together with

utility’s power delivery infrastructure may also

and grounding errors within the healthcare

one downstream system depending upon the

be prohibitively costly. Given that the cost of

facility’s electrical system. Prior to the

results from an upstream system. Instead,

the events and facility-level solutions can be

decision to purchase and install a large UPS, a

each piece of medical equipment is designed

very expensive, electric utilities and their

well-developed power quality investigation

to carry out a specific task such as monitoring

healthcare customers search for ways to ease

should be done within the facility to determine

blood pressure, monitoring blood oxygen

the financial burden of increasing the immunity

the extent to which wiring and grounding

level, and providing breathing assistance to a

of their healthcare customers to common

errors contribute to the root cause of

patient. However, the typical solutions that

electrical disturbances such as voltage sags,

malfunctions with small and large medical

can be applied in manufacturing environments

momentary interruptions, and surges.

loads. In almost all situations, typical wiring

to solve power quality problems with

and grounding errors internal to the facility can

industrial equipment can also be applied to a

Healthcare providers are not willing to install a

be linked to the severity of common

healthcare facility.

power mitigation device on each piece of medical equipment. However, they can be

disturbances entering the facility from

12

everyday electrical events occurring on the

The types of portable electronic medical

persuaded to have their maintenance staff sift

utility power system and from events

equipment that can be fitted with a low- to

through the details of a facility’s power

generated by the operation of large loads in

mid-power UPS are limited (to some less than

distribution system through learning how to

neighboring customer facilities and/or

10 kVA machines. Because of the need to

conduct power quality investigations.

generated by the operation of large loads

provide safe patient environments, most

Moreover, healthcare providers may also be

within the healthcare facility.

typical power quality solutions, such as

persuaded to improve their medical

constant voltage transformers and sag-

equipment procurement process by learning

Purchasing and installing large UPS systems

reducing technologies, cannot be

how to specify an acceptable level of

to protect individual imaging systems or

implemented on medical equipment in the

immunity to voltage sags and momentary

several systems in a medical imaging suite

patient environment. Most medical

interruptions and voltage surges that is

can present additional problems for the

equipment are designed to be portable and

suitable to most healthcare facility electrical

healthcare provider. Healthcare facility

are placed on high-quality equipment carts

environments. But, before this concept can be

designers do not make accommodations for

without space provided for a UPS. Some

widely applied, medical equipment

such large pieces of power mitigation

devices such as blood-pressure monitors and

manufacturers must succumb to determining

equipment. Healthcare providers, operating on

infusion pumps must have power maintained

the full immunity capability of their equipment

extremely tight budgets, do not budget for the

to them as the patient is moved throughout

to these common disturbances.

Power Quality for Healthcare Facilities

Power quality in the healthcare environment can be improved through enhancing the level of awareness among utilities, healthcare facility designers, and medical equipment manufacturers.

IMPROVING POWER QUALITY IN THE HEALTHCARE ENVIRONMENT

fewer electrical disturbances, „ effectively use power-conditioning

Power quality in the healthcare environment

technologies for existing medical

can be improved through enhancing the

equipment in accordance with

level of awareness among the stakeholders:

standards and recommended

utilities, healthcare facility and medical

practices,

staff, healthcare facility designers, and medical equipment manufacturers. Power quality problems in this mission-critical environment present a series of challenges among stakeholders. Meeting these challenges helps to prevent these problems

„ carefully plan new construction or

renovation of existing healthcare facilities with regard to power quality concerns, „ maintain existing wiring and medical

before they become monumental to

equipment in healthcare facilities,

healthcare providers.

and „ learn from past power quality

Meeting the Power Quality Challenges of the Healthcare Industry Although healthcare staffs rely upon advanced medical procedures using advanced medical equipment to provide immediate patient care, they must sometimes plug equipment into antiquated and unreliable electrical systems. Moreover, some equipment manufacturers design equipment without fully considering and understanding the electrical environment of a healthcare facility. Because of its obligation to human care, the healthcare industry must demand high standards of performance from facility designers, equipment manufacturers, equipment service companies, facility and equipment support staff, and electric supply companies. To meet the challenges of the healthcare industry, these people must meet on common ground to „ establish new partnerships to

improve power quality in the healthcare environment, „ improve the procurement process for

new medical equipment, „ encourage equipment manufacturers

13

disturbances and that generates

problems.

Establishing Partnerships Preventing or resolving power quality problems should be a cooperative effort between healthcare facilities, equipment vendors, equipment manufacturers, and electric supply companies. Electric supply companies have always offered assistance to customers in emergencies and have sometimes promoted new energy-efficient technologies to improve productivity and reliability as well. As problems associated with new technologies were revealed, many electric supply companies established power quality programs that invested in power quality research to assist utility customers and manufacturers with equipmentcompatibility problems. Electric supply companies especially recognize the necessity of identifying or providing power quality engineering services to their healthcare customers. These services enable healthcare staff to learn how to identify wiring and grounding problems that exacerbate power quality problems, select the proper power-

to design medical equipment that is

conditioning equipment to mitigate these

more immune to electrical

problems, develop specifications (that

Power Quality for Healthcare Facilities

Building strong relationships between healthcare facilities, equipment vendors, equipment manufacturers, and electric supply companies offers many benefits.

include power quality specifications) for

and clinics where significant and

purchasing medical equipment problems,

costly power quality problems have

establish correct installation guidelines, and

occurred find it cost-effective to

plan center renovations or the construction

purchase a monitor and learn to use

of new healthcare facilities and medical

it. Consider tapping the expertise of

clinics to help avoid problems.

your local utility company or independent consultants. Determine

Building strong relationships between

the characteristics of your facility’s

healthcare facilities, equipment vendors,

electrical system: Can it tightly

equipment manufacturers, and electric

regulate equipment voltage? Is

supply companies offers many benefits.

voltage to equipment continuous?

These benefits include learning how to avoid

Does high-wattage equipment create

wiring and grounding errors, reducing or

electrical disturbances in the facility

eliminating controllable electrical

wiring? Your local utility company

disturbances, managing common

may also provide site-specific

uncontrollable electrical disturbances,

characteristics such as expected

encouraging equipment manufacturers to

voltage regulation and statistical

design and build robust equipment immune

analysis of electrical disturbances.

to most electrical disturbances, significantly reducing the potential for lawsuits by healthcare patients involved in events possibly initiated by equipment malfunctions, and avoiding citations and penalties from international regulatory agencies.

„ Evaluate the immunity performance

requirements of existing equipment. How susceptible is each type of medical equipment to common electrical disturbances such as voltage sags and transient overvoltages? „ Set your expectations for the

Creating a Power Quality Checklist for Procuring Equipment

performance of new equipment, and

Healthcare facilities and medical clinics

help in specifying design features

routinely procure and install medical,

that enhance compatibility between

functional, and facility equipment. To

the equipment and its intended

reduce power-quality-related problems

electrical environment.

between equipment and the intended electrical environment, equipmentprocurement procedures should include the following steps.

then ask your utility company for

„ Identify and repair all wiring and

grounding problems. „ Identify all areas where critical

electronic medical equipment may Planning for Additional Equipment „ Begin a sound in-house power

quality program with the purchase of a PQ monitor to conduct an on-site survey to identify potential power quality problems and diagnose problems with sensitive electronic

be used and the special power requirements of such equipment. „ With assistance from your local

utility company or independent consultants, identify appropriate power-conditioning devices for critical electronic equipment.

medical equipment. Some facilities

14

Power Quality for Healthcare Facilities

Purchasing Additional Equipment „ Disclose to equipment suppliers the

Installing Additional Equipment „ Use high-performance wiring and

power quality characteristics of the

proper grounding techniques

electricity and wiring where the new

specified in the International

equipment will be installed.

Electrical Code (IEC), the Institute of

„ Ask the manufacturer’s representative

about known power quality problems with the equipment and if the equipment has been tested for compatibility with the utility power system. If there is reason to believe that compatibility may be an issue, ask to see the power quality test report. „ For all new equipment, specify the

voltage range (required voltage regulation), frequency, and voltage sag immunity (i.e., ride-through) performance.

Electrical and Electronics Engineers (IEEE) Standard 602-1996 (White Book; Recommended Practice for Electric Systems in Healthcare Facilities), and the IEEE Standard 1100-1992 (Emerald Book; Powering and Grounding Sensitive Electronic Equipment). „ For circuits connected to sensitive

electronic equipment, use singlepoint grounding, locate equipment as electrically close to the source as possible, and make sure that the sizing of phase, neutral, and ground

„ Purchase equipment with an input

conductors follow international and

voltage rating matched to the voltage

local codes and manufacturer

at the installation site when possible.

installation requirements.

Purchase high-quality matching transformers with new equipment when the voltage ratings of the equipment do not match the available voltage at the installation site.

„ When adding grounding conductors

to an existing facility, run the grounding conductors parallel to the existing power conductors to reduce stray electromagnetic fields.

„ If a power-conditioning device is

needed, make sure that it is designed for compatibility with electronic medical equipment. Medical equipment such as imaging systems with dynamic load behavior may not function properly when connected to some power conditioners.

„ When installing high-wattage

medical equipment in an existing facility, monitor the input voltage at the proposed installation site for electrical disturbances for at least a 30-day period before completing the installation.

„ Make sure that all medical and

power-conditioning equipment complies with applicable

„ Regularly review equipment

international codes, standards, and

performance and continue the

recommended practices.

relationship between healthcare

„ To reduce susceptibility to common

15

Maintaining Equipment

facility staff, utility company

electrical disturbances, select the

representatives, equipment vendors,

highest input voltage rating for

equipment manufacturers, and

equipment known to be sensitive to

medical equipment service

common electrical disturbances.

companies.

Power Quality for Healthcare Facilities

„ Document all facility power outages,

noticeable disturbances (i.e., light flicker), and equipment problems.

Using Power-Conditioning Devices to Improve Equipment Compatibility Some power quality problems in healthcare

Include patient schedules, the location of equipment, the

facilities and medical clinics can be solved with appropriate power-conditioning

symptoms, suspected causes, time

devices. Some of these technologies are listed in the table on the left and include

and date of occurrence, and any other related events. Checking

isolation transformers, surge-protective

disturbance logs against utility company records and facility

devices, voltage regulators, and UPSs.

activities can help reveal the source

However, power-conditioning devices are

of electrical disturbances. These logs can also be used to specify future

not always the answer to a power quality

equipment purchases and determine correct installation methods.

quality mitigation equipment can worsen a

problem. In some cases, installing power medical equipment malfunction, especially in cases where medical equipment loads are

General Summary of Available Power-Conditioning Technologies

very dynamic in nature, like that of diagnostic medical imaging equipment. In addition, low-kilovolt-ampere powerconditioning devices and “ice-cube” relays, power supplies, and contactors routinely used in industrial facilities can be used in the physical plants (i.e., where HVAC, steam, air, vacuum, and other mechanical systems are located) but cannot be used with medical equipment to solve power quality problems. In other cases, installing such equipment is not necessary and can have no effect on the problem. For example, power-conditioning devices will not protect equipment against radiated emissions or electrostatic discharge, which has been reported as one of the electromagnetic-related causes of equipment malfunction. In some cases, the potential for this problem can be virtually eliminated by maintaining correct humidity levels or installing building materials that reduce the buildup of static charge. In other cases where wiring and grounding problems exacerbate equipment malfunctions caused by voltage transients, installation of a UPS can provide enhanced immunity to voltage sags and momentary interruptions and some mitigation of transients. However, if equipment damage is

16

Power Quality for Healthcare Facilities

Good grounding is essential for good power quality and safety at any healthcare facility.

caused by a wiring and grounding problem and voltage transients developed at the point of use (where the equipment is connected to the center electrical system), then installing an upstream UPS will not resolve the problem. Consult the equipment

„ medical equipment such as imaging

and radiology equipment and medical air pumps, and „ mechanical equipment such as

adjustable speed drives, chillers, fans, pumps, and HVAC equipment.

manufacturer and local utility company to determine whether a power-conditioning device can be used effectively.

Other support equipment, such as biomedical and laboratory equipment and low-power kitchen and laundry equipment,

Understanding Facility Voltage Requirements, Grounding, and Dedicated Circuits

are powered at 120 volts.

The voltage level provided to the service

tolerance levels for the electric supply

entrance of a healthcare facility will impact

voltage with a range of ±10% will again be

the voltage that is provided to all loads in

unified for European healthcare facilities

the facility, especially the medical

and medical clinics. Thus, European

equipment loads. Because the healthcare

manufacturers of medical equipment used

provider must provide healthcare services to

in the United States, who have integrated

patients in real-world power quality

design changes into their equipment to help

environments, grounding the facility

ensure reliable operation in Europe, may

infrastructure, the secondary of the utility

find that United States users file fewer

company’s transformer at the service

complaints regarding medical equipment

entrance, within the switchgear, throughout

malfunctions. Healthcare facilities and

the facility electrical system, and at the end-

medical clinics in the United States may

use level where the equipment is connected

experience fewer malfunctions caused by

and used is also critical. Moreover, many

long-term steady-state undervoltage

end-use loads in healthcare facilities require

conditions and possibly minor voltage sags.

the use of a dedicated feeder or branch

In areas such as medical laboratories where

circuit, which helps to maintain voltage and

microscopes are used and surgical suites

current quality to critical equipment.

where eye surgery and other surgical

However, effective January 1, 2008, the

procedures are performed, high power The voltage levels selected for new

quality lighting that is immune to more

equipment will depend upon the available

types of voltage fluctuations and other

utility voltage, the size of the healthcare

electrical disturbances may operate with

facility or medical location, voltage levels

less flicker to lamps, thus improving light-

used within, type of equipment, building

assisted and light-dependent medical

layout, voltage regulation requirements, and

procedures.

cost. Typically, power to a healthcare facility or medical location is supplied by the utility company at a medium voltage level for large

Voltage Matching

facilities and clinics and at 480 volts (with a

Once the nominal voltages of equipment

±5% range), three-phase. These voltages

have been selected, the voltage source for all

may be used to power:

medical equipment to be installed in the facility should be carefully checked to assure proper voltage levels. New equipment

17

Power Quality for Healthcare Facilities

should be ordered to match one of the

However, the focus of the discussion in this

planned voltage sources. Otherwise consider

section of this report is not on patient

using buck/boost transformers,

safety, but on wiring and grounding (i.e.,

autotransformers, or standard two-winding

earthing systems) as they relate to power

isolation transformers to match the voltage

quality in U.S. healthcare facilities and

requirement of the equipment to the voltage

medical clinics. Moreover, the compatibility

source. Variacs should never be used to

between medical equipment and the

match a source voltage to an equipment

electrical environment in these facilities and

voltage.

clinics is dependent upon the type of earthing system that powers and grounds

Regardless of the earthing system used, providing a solid lowimpedance ground to sensitive equipment will help minimize power quality problems.

Equipment from International Manufacturers

Equipment purchased from international sources originally designed to operate in countries with different nominal voltage levels requires careful consideration of the design of the facility distribution system so that the correct voltage can be supplied to the equipment. Equipment designed for nonstandard U.S. voltages may require matching transformers. The addition of a transformer may make equipment more sensitive to common electrical disturbances. Also, equipment designed for 60-hertz operation must be able to operate properly at 60 hertz. The voltage tolerance of overseas equipment may also be a concern and should be checked. Equipment purchased from European manufacturers not recognizing the standard U.S. nominal voltage may require a special transformer to be powered from U.S. voltage sources.

the medical equipment. Regardless of the earthing system used, providing a solid low-impedance ground to sensitive equipment—which is required by the NFPA NEC and healthcare facility codes and recommended by the IEEE Emerald, Green, and White Books—will help minimize power quality problems. Because patients are often moved from one location in the healthcare facility to another, grounded receptacles should be available at all possible equipment locations. Power cords should never be modified to accommodate an ungrounded receptacle by removing the grounding connector. Nor should grounding adapters be used on equipment requiring a ground. In some older healthcare facilities, grounding conductors may be present but may not be running parallel to the power conductors. In the course of enhancing the grounding system in these facilities, the grounding conductors should be run parallel to the circuit’s neutral and power

Ensuring Proper Grounding and Wiring

conductors, which will minimize stray

Power quality investigations carried out in

electromagnetic fields due to the presence

the United States are revealing that the

of any unwanted ground currents.

integrity of wiring and grounding systems in healthcare facilities and medical clinics has

Similar to the requirements of electrical

an even greater impact on the immunity of

systems for providing quality voltage and

medical equipment to common electrical

current to large loads such as chillers and

disturbances. Since the term leakage current

printing presses found in commercial and

was coined for the medical equipment

industrial facilities, large loads in healthcare

industry, much of the focus on the integrity

facilities must be circuited such that their

of grounding systems in healthcare facilities

operation does not affect other loads.

has been on patient safety.

Powering disturbance-generating loads such as HVAC equipment (e.g., motor contactors,

18

Power Quality for Healthcare Facilities

To avoid equipment malfunctions during renovation or new construction, healthcare facility engineers should coordinate with construction foremen before the electrical system is modified.

motor starters, chillers, heating systems,

The IEEE Standard 602 (White Book), and

etc.) from the same voltage bus that powers

IEEE Standard 1100 (Emerald Book) are also

critical medical loads (e.g., X-ray equipment

both excellent technical resources that

and medical imaging systems) is a

address power quality in healthcare facilities

prescription for incompatibility problems

and medical clinics and offer guidance on

between building and facility loads, and

powering and grounding sensitive electronic

critical medical loads. Large diagnostic

equipment during facility construction.

medical imaging systems, such as MRI systems, CT scanners, and various X-ray

Medical Equipment Power Supplies

machines require dedicated power, neutral, and ground conductors also, because they usually draw fluctuating dynamic currents. Providing dedicated conductors for power, neutral, and ground is not only concerned with individual circuits (i.e., the fact that the circuits are separate runs from switchgear and electrical panels) but also the size (i.e., wire gauge) of the conductors with respect to the required length and the allowable voltage drop from the supply to the load. Many power quality investigations result in findings that identify dedicated circuits to X-ray equipment and imaging systems that are sized too small in wire gauge. The size of the grounding conductor is also important and should be specified according to the requirements of the X-ray or medical imaging system manufacturer. When this equipment is installed, the facility electrician should also determine what other sensitive or disturbance-causing equipment may be powered by the common source. In some cases, the solution may require providing a dedicated circuit to certain sensitive medical equipment to isolate it from other disturbance-causing equipment.

In healthcare facilities and medical clinics, the failure of the facility power may pose life-threatening consequences to patients. Examples of these concerns are the failure of a power supply in a ventilator, a lighting system in an operating room, and the branch circuit to a life support system in an ICU. The restoration time for medical power supplies to restore power to the medical equipment is not specified in the United States for medical microprocessor-based equipment. Designers of medical power supplies must be conscious of the amount of leakage current they allow to flow out of the supply under certain conditions, and the allowed levels are governed by the Association for the Advancement of Medical Instrumentation (AAMI). Lower leakage currents equate to higher levels of conducted emissions, thus increasing the likelihood of a medical device creating an electromagnetic interference (EMI) problem. Careful balance between EMI filter design and leakage current helps to ensure success in both areas. However, as medical devices become more digital in the next 20 years, this balance will become more

To avoid equipment malfunctions during

difficult to achieve.

renovation or new construction, healthcare facility engineers should talk to the

Standards

designated construction contact before the

The healthcare and medical equipment

electrical system is modified. This

industries are heavily regulated to protect

precaution will help ensure that good power

patients. Both the United States and Europe

quality is maintained on circuits deemed

have developed and published standards,

essential to patient safety, critical care, and

recommended practices, and guidelines

other equipment necessary for the effective

related to power quality and

operation of the healthcare facility during

electromagnetic compatibility in the areas

the construction and renovation process.

19

Power Quality for Healthcare Facilities

of healthcare facility design, medical equipment design (i.e., product standards), and emergency preparedness. Standards, recommended practices, and guidelines have also been developed that define disturbances and test methods for power quality and electromagnetic compatibility. The United States has made significant

„ EN 61000-3-X: Emissions, limits „ EN 61000-4-X: Emissions,

measurement techniques „ EN 61000-5-X: Immunity, testing

techniques „ EN 61000-6-X: Installation and

mitigation guidelines

contributions in power quality standards and healthcare facility design standards.

Other healthcare codes, standards, and

Europe has made significant contributions

recommended practices are promulgated by

in the area of immunity standards (i.e.,

the NFPA, the IEEE, the American National

emissions and immunity) regarding product

Standards Institute (ANSI), the Federal

design and safety.

Communications Commission (FCC), the IEC, and the International Special

The top table on the following page presents

Committee on Radio Frequency (CISPR).

a summary of power-line and electromagnetic disturbances, power electronics technologies, emissions and

Healthcare Facility Standards

immunity standards, and equipment

Standards, recommended practices, and

performance standards relating to electronic

guidelines have also been developed in

medical equipment. Medical equipment

several areas related to the design of

designers and manufacturers in the United

healthcare facilities and medical clinics. The

States have become more cognizant of these

NFPA 99 (Standard for Healthcare Facilities),

standards. The emissions and immunity

the facility code standard developed and

standards listed in the bottom table on the

used in the United States; the NFPA

following page are the Basic

Standard 70 (The National Electric Code),

Electromagnetic Compatibility (EMC)

the electrical code standard developed in

standards prepared by the European-based

the United States; and the IEEE Standard

International Electrotechnical Committee

602-1996, White Book (Recommended

(IEC). In the past few years, they have been

Practice for Electric Systems in Healthcare

referred to as IEC 61000-X-X standards. After

Facilities), the electrical system design

the European Union (EU) recently adopted

practice developed and used in the United

them as European Norms (EN) standards,

States, provide guidance to designers of

they were referred to as EN 61000-X-X

healthcare facilities and medical clinics.

standards. The requirements listed in these

Facility designers in the United States also

standards serve as the basis for all present

commonly refer to the well-known IEEE

and future power quality and EMC

Standard 1100-2006, Emerald Book (Powering

requirements for all products traded

and Grounding Sensitive Electronic

internationally, including electronic medical

Equipment), for guidance on powering and

equipment. The Basic EMC standards

grounding electronic medical equipment.

consist of the following six parts: „ EN 61000-1-X: General EMC

standards „ EN 61000-2-X: Compatibility levels of

environments Continued on page 22 20

Power Quality for Healthcare Facilities

21

Power Quality for Healthcare Facilities

Cross-Reference of European Standards Applicable to Electromagnetic Compatibility of Electronic Medical Equipment

(Refer to table below)

Effects of Electromagnetic Disturbances on Power Electronics Technologies Used in Electronic Medical Equipment

Healthcare facility standards address important aspects of the electrical system in a healthcare facility from planning, voltage selection, loading, harmonics, disturbances, mitigation techniques, emergency power systems, renovation, telecommunica tions, and lighting.

Continued from page 20

strength, and isolation transformer

Healthcare facility standards address every

construction to enable its use in electronic

aspect of the electrical system in a

medical equipment. The “Y” capacitors

healthcare facility from planning; voltage

required in the input filter of a standard

selection; loading (e.g., historical load

switch-mode power supply for information

densities and profiles, demands, and

technology equipment would almost

factors); harmonics; disturbances;

certainly cause the power supply to fail on

mitigation techniques; emergency power

the grounds of excessive leakage current.

systems; renovation; telecommunications;

Briefly, the more-stringent requirements

and lighting. Guidance is given on how to

that are of particular relevance to power

avoid overloading, undervoltaging,

supplies used in electronic medical

overvoltaging, and equipment damage and

equipment are (1) service entrance to

shutdown caused by power problems.

secondary creepage and clearance distances for double or reinforced insulation for

Medical Equipment Safety Standards

equipment operating from 250 volts AC maximum must be 8 and 5 millimeters,

In the EU, technical safety problems of

respectively; (2) primary to secondary

electronic medical equipment are addressed

dielectric withstand test must be 4,000 volts

by the EN 60601 series of standards which

AC; (3) earth leakage current maximum is

follow IEC 601 (now referred to as IEC

0.5 milliamp for normal operation and 1

60601-1-2), Medical Electrical Equipment. In

milliamp maximum for a single fault

the United States, UL 544, Medical and

condition. These values are for type B, type

Dental Equipment, covers medical and

BF, and type CF equipment categories:

dental equipment, but in 1994 UL 2601-1, Medical Electrical Equipment—Part 1: General Requirements for Safety, came into effect. This standard is harmonized with IEC 60601-1-2, to be used at present in parallel with UL 544, Medical Equipment, and the U.S. safety standard for medical equipment, but it became the sole mandatory standard in 2004. In Canada, CSA 22.2-601.1, Medical

„ Type B—Non-patient-connected

equipment, or equipment with grounded patient connection. „ Type BF—Equipment with a floating

patient connection. „ Type CF—Equipment with a floating

connection for direct cardiac application.

Electrical Equipment—Part 1: General

22

Requirements for Safety, has been in use

Patient leakage current for the above

since 1990, again, alongside the existing

categories is 0.1 milliamp (0.5 milliamp for a

standard CSA 22.2-125, Electromedical

single fault condition) for type B and BF and

Equipment, and it became the sole

0.01 milliamp (0.05 milliamp for a single

applicable standard in the year 2000.

fault condition) for type CF.

The bulk of the electrical safety

In the EU, electronic medical equipment is

requirements detailed in IEC 60601-1-2 are

subject to the Medical Device Directives 93-

based on IEC 950, Safety of Information

42-EEC, which was implemented on January

Technology Equipment Including Electrical

1, 1995. These “New Approach” Directives

Business Equipment. However, an IEC 950

gave a three-year transitional period (up to

(EN 60950) approved power supply would

January 1, 1998) until CE marking (mandatory

need to pass the additional test and

marking to indicate conformity with the

inspection requirements of EN60601-1 for

health and safety requirements set out in the

separation, leakage current, dielectric

European Directives) was required.

Power Quality for Healthcare Facilities

Two New Approach Directives, 90/385/EEC Active Implantable Medical Devices (AIMD) and 93/42/EEC Medical Devices Directive (MDD) exempt those specific product categories from the EMC Directive. They contain their own specific EMC requirements. Probably only the MDD will be of interest to power supply designers and users. The EMC standards cited are IEC60061-1-2, adopted by European Committee for Electrotechnical Standardization (CENELEC) and published as EN60601-1-2. Emission standards required follow CISPR 11 (EN55011), Limits and Methods of Measurement of Electromagnetic Disturbance Characteristics of Industrial, Scientific, and Medical (ISM) Radio Frequency Equipment, normally class B, with a 12-dB relaxation for radiated emissions in X-ray rooms, for example. Immunity standards again rely heavily on IEC 801 as follows: „ IEC 801-2, Electrostatic Discharge:

3 kV contact, 8 kV air „ IEC 801-3, Radiated Radio-Frequency

Interference (RFI): 3 V/m from 26 to 1000 MHz, 80% amplitude modulation, 1 V/m in X-ray rooms

„ IEC 801-4, Electric Fast Transients:

1 kV at service entrance plug, 2 kV for hardwired service entrance, 0.5 kV on connecting leads greater than 3 m long „ IEC 801-5, Service Entrance Surges:

1 kV differential, 2 kV common mode After June 14, 2000, electronic medical equipment was allowed to be sold within the EU as compliant with either the EMC or MD Directives. An important point to note for all products subject to the AIMD, and many products under the MDD (except class I), is that they cannot be self-certified. Approvals must be carried out by Notified Test Organizations. Class I equipment is defined as equipment for which electric shock protection is achieved by basic insulation and protective earth. All conductive parts that could assume hazardous voltages in the event of failure of basic insulation must be connected to a valid protective earth conductor. The table below lists some additional medical equipment performance standards.

U.S. and European Electromagnetic Compatibility Standards Applicable to Healthcare Facilities and Electronic Medical Equipment

23

Power Quality for Healthcare Facilities

CONCLUSION

Important information has been provided here about how healthcare facilities and medical clinics view power quality problems, how such problems can be recognized by facility and medical staffs, definitions of the sources of electrical disturbances that can impact healthcare facilities and medical clinics, and how power quality challenges might be met in a complex environment where patient safety must prevail above power quality. Recognizing and correcting wiring and grounding errors and the commingling of loads are paramount in resolving power quality problems in healthcare facilities and medical clinics, and establishing partnerships between electric supply companies, facility designers, medical equipment manufacturers, and the facility and medical staffs is also critical. This approach is based on common practices employed in U.S. healthcare facilities to understand, identify, solve, and prevent

power quality problems. The information provided in the PQ TechWatch “Hardening Manufacturing Processes Against Voltage Sags” (EPRI, 200) can also be applied to the physical plant of healthcare facilities and medical clinics in efforts to harden mechanical equipment against voltage sags and momentary interruptions. Most voltage sag-sensitive components typically found in a healthcare facility or medical location cannot be placed on a power conditioner at the patient level. Diagnostic medical imaging systems are ultrasensitive to voltage disturbances, and many times these systems are not compatible with a UPS or cannot be placed on a power conditioner due to cost and space limitations in imaging suites. The cost of resolving underlying wiring and grounding errors and separating disturbance-causing loads from sensitive medical equipment is typically much less than the cost of placing an entire department or facility on conditioned power.

BIBLIOGRAPHY Capuano, Mike, Patrick Misale, and Dan Davidson, “Case Study: Patient-Coupled Device Interaction Produces Arrhythmia-Like Artifact on Electrocardiographs,” Biomedical Instrumentation & Technology, November/December 1993, pp. 475–483. Dorr, Douglas S., and Douglas C. Folts, “UPS Response to Power Disturbances,” Medical Electronics Magazine, December 1994, pp. 48–56. IEC 601-1-02, Medical Electrical Equipment, Part 1: General Requirements for Safety. 2. Collateral Standard: Electromagnetic Compatibility—

Requirements and Tests, 2nd edition (Geneva: International Electrotechnical Commission, June 1996). IEEE Standard 1602-1996, Recommended Practice for Electric Systems in Health Care Facilities—IEEE White Book (Piscataway, NJ: Institute of Electrical and Electronics Engineers, 1996). Keebler, Philip F., “Power Quality for Diagnostic Medical Imaging Systems,” EPRI, November 2006. Keebler, Philip F., “Power Quality for Healthcare,” BR-109172 (White Plains, NY: EPRI Healthcare Initiative, 1997). Keebler, Philip F., “Solving Power Quality Problems in Medical Imaging Systems,” PB-106393 (Knoxville, TN: EPRI Power Electronics Applications Center, 1996) Lamarre, Leslie, “Power Prescriptions for the Health Care Industry,” EPRI Journal, June 1994, pp. 14–21. Loznen, Steli P., “Product-Safety Requirements for Medical Electrical Equipment,” Compliance Engineering Magazine, March/April 1995, pp. 17–29. Russell, Michael J., “Cardiovascular Imaging Equipment Requires Emergency Power,” Power Quality Magazine, January–March 1992, pp. 8–19. Waterman, Craig, “Medical Facility Power Quality Problems Can Be Deadly,” Power Quality Magazine, Premier II 1990, pp. 82–90. Whitfield, John, The Electricians Guide to the 16th Edition of the IEE Wiring Regulations BS 7671 and Part P of the Building Regulations (Wendens Ambo, Essex: EPA Press, March 2005).

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Power Quality for Healthcare Facilities