The document discusses electrical safety testing of medical equipment. It begins by introducing the importance of electrical safety testing to ensure patient safety and meet regulatory standards. It then covers common electrical hazards for medical devices, the physiological effects of electricity on the human body, and international standards for electrical safety testing (IEC 60601 and IEC 62353). The document concludes by describing the specific tests performed during an electrical safety test, including earth resistance testing, insulation testing, and leakage current testing.

1. Basics of Electrical Safety
Testing
Electrical Safety Testing of Medical Equipments
Mehaboob Rahman
Barq Consulting Engineers
Healthcare Technology Management, KFMC

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TABLE OF CONTENTS
1 Introduction
2
Hazards
Common Hazards on Medical Equipments
3
Basics of Electrical Safety
Physiological Effects of Electricity on the Body
4
Electrical SafetyTesting
Why do we need Electrical Safety Test
Terminologies of EST
Class of Medical Equipments
Types of Medical Equipments
5
International Electrotechnical commission
IEC 60601
IEC 62353
6
Electrical SafetyTesting Procedure
How Testing is performed
Documentation
Visual Inspection
Earth ResistanceTest
Insulation Test
Leakage Current Test
7 Conclusion

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Introduction
Medical technology has substantially improved health care in all medical specialties
and has reduced morbidity and mortality for critically ill patients.
However, the increased complexity of medical devices and their utilization in more
procedures result in about 10,000 device- related patient injuries in USA.
Most of these injuries are attributable to improper use of devices as a result of
inadequate training and lack of experience. Medical personnel rarely read user
manuals until a problem has occurred. Furthermore, medical devices eventually fail,
so engineers must develop fail-safe designs.

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HAZARDS
A hazard is any biological, chemical, mechanical, environmental or physical agent that is reasonably
likely to cause harm or damage to humans, other organisms, or the environment in the absence of its
control.
Most hazards are dormant or potential, with only a theoretical risk of harm; however, once a hazard
becomes "active", it can create an emergency. A hazardous situation that has come to pass is called
an incident. Hazard and possibility interact together to create risk
Hazards on Medical Equipments
Medical electrical equipment can present a range of hazards to the patient, the user, or to service
personnel.
Many such hazards are common to many or all types of medical electrical equipment, whilst others
are peculiar to particular categories of equipment.
The root causes for injures involving medical equipment include Human Error, Faulty Equipment
Design & Poor Maintenance. However, It is unwise to assume anything until a through investigation is
made and failure analysis is performed on the equipment.
Common Hazards of Medical Equipments.
Mechanical Hazards
All types of medical electrical equipment can present mechanical hazards.
These can range from insecure fittings of controls to loose fixings of wheels on equipment
trolleys.
The former may prevent a piece of life supporting equipment from being operated properly,
whilst the latter could cause serious accidents in the clinical environment.
The Enclosure
The enclosure of the device must be sufficiently strong to retain its integrity under conditions of
normal wear and tear
Handles of portable equipment are tested with a force of four times the weight of the product. If
there is more than one handle, this weight is distributed between the handles.
Moving Parts
Moving parts which could produce a safety hazard must be suitable guarded to prevent access,
unless exposure is essential to the operation of the equipment.
If movement of the equipment, or parts of the equipment can cause injury to the patient, this
movement can only be achieved by continuous operation of the control by the operator.
Any electrically controlled mechanical movement must have an emergency switch.
Sharp Edges - The device must not have sharp edges, corners, etc.
Stability - Medical devices must not overbalance when tilted to an angle of 10°.

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Risk of Fire or Explosion
All mains powered electrical equipment can present the risk of
fire in the event of certain faults occurring such as internal or
external short circuits.
In certain environments such fires may cause explosions.
Although the use of explosive anesthetic gases is not common
today, it should be recognized that many of the medical gases
in use vigorously support combustion.
Medical devices typically contain a number of electro-mechanical and chemical systems and
power sources. Power can be supplied to an actuating mechanism, or fluids and gases can be
handled through compression, dispersion or valving. The devices typically contain items that
include foamed padding and/or structural plastics. All of these things in combination present an
energy source for ignition, fuel and oxidizer – good conditions for fire ignition and propagation.
Absence of Function
Since many pieces of medical electrical equipment are life supporting or monitor vital functions,
the absence of function of such a piece of equipment would not be merely inconvenient, but
could threaten life
This recommend the use of proper test equipments to verify the correct operation of the
equipment.
Excessive or insufficient output
In order to perform its desired function equipment
must deliver its specified output.
Too high an output, for example, in the case of
surgical diathermy units, would clearly be
hazardous. Equally, too low an output would result
in inadequate therapy, which in turn may delay
patient recovery, cause patient injury or even
death.
This highlights the importance of correct
calibration procedures
Infection
Medical equipment that has been inadequately decontaminated after use
may cause infection through the transmission of microorganisms to any
person who subsequently comes into contact with it.
Clearly, patients, nursing staff and service personnel are potentially at risk
here.

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Misuse
Misuse of equipment is one of the most common causes of adverse incidents involving medical
devices.
Such misuse may be a result of inadequate user training
or of poor user instructions.
Do not modify or alter devices, unless in the instructions
for use it is clear that the manufacturer sanctions the
modification or alteration.
Radiation Hazard
The medical use of ionizing radiations, whether for diagnosis or therapy, not only results in the
irradiation of the patient but may also result in some degree of exposure of radiologists,
radiographers, other workers of the department.
Although many patients benefit from radiation’s ability to destroy cancer cells or capture real-
time images of the human body, radiation can harm healthy cells wherever it enters the body. It is
well documented that ionizing radiation can cause damage ranging from uncontrollable cell
replication to cell death.
Risk of exposure to spurious electric currents
All electrical equipment has the potential to expose people to the risk of spurious electric
currents. In the case of medical electrical equipment, the risk is potentially greater since patients
are intentionally connected to such equipment and may not benefit from the same natural
protection factors that apply to people in other circumstances.
Whilst all of the hazards listed are important, the prevention of many of them require methods
peculiar to the particular type of equipment under consideration. For example, in order to avoid
the risk of excessive output of surgical diathermy units, knowledge of radio frequency power
measurement techniques is required.
However, the electrical hazards are common to all types of medical electrical equipment and can
minimized by the use of safety testing regimes which can be applied to all types of medical
electrical equipment.

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BASICS OF ELECTRICAL SAFETY
Electrical Safety
Electrical safety is very important in hospitals as patients may be undergoing a diagnostic or
treatment procedure where the protective effect of dry skin is reduced. Also patients may be
unattended, unconscious or anaesthetized and may not respond normally to an electric current.
Further, electrically conductive solutions, such as blood and saline, are often present in patient
treatment areas and may drip or spill on electrical equipment.
Electric Current
Injuries received from electric current are dependent on the magnitude of current, the pathway
that it takes through the body and the time for which it flows.
The nature of electricity flowing through a circuit is analogous to blood flowing through the
circulatory system within the human body. In this analogy the source of energy is represented by
the heart, and the blood flowing through arteries and veins is analogous to current flowing
through the conductors and other components of the electric circuit.
The application of an electric potential to an electric circuit generates a flow of current
through conductive pathways. This is analogous to the changes in blood pressure caused by
contraction of cardiac muscle that causes blood to flow into the circulatory system. For
electric current to flow there must be a continuous pathway from the source of potential
through electrical components and back to the source.
Physiological Effects of Electricity on the Body
What will happen when current flows through biological tissue?
Human body can easily bear electrical current of 1 milliampere passing through its body without
appreciable risk or damage. However, as the amount of current increases the body may suffer
different type of damages like. Fibrillation, Burns to parts of the body due to heat generated by
electricity, Damage to nervous system causing loss of nervous control.
When the current passes through brain it can lead to unconsciousness and permanent damage to the
brain. including death or electrocution
The physiological effects of electrical shock include the following.
 Electrolysis (mainly near d.c.)
 Neuromuscular effects (mainly 10-100Hz)
 Heating (mainly 100KHz-30Mhz)

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Electrolysis
The movement of ions of opposite polarities in opposite directions through a medium is called
electrolysis.
Electrolysis can be made to occur by passing DC current through body tissues or fluids.
If a DC current is passed through body tissues for a period of minutes, ulceration begins to occur.
Such ulcers, while not normally fatal, can be painful and take long periods to heal.
The formation of sodium atoms at the negative electrode and chlorine atoms at the positive
electrode causes local chemic al actions which kills the cells.
Neuromuscular Effects
Macroshock
Macroshock is the most common type of shock received and occurs when the human body becomes
a conductor of electric current passing by means other than directly through the heart. This effect can
readily occur with the use of medical electrical equipment as the natural resistance of the skin to
current flow is often reduced or bypassed by electrodes and electorde paste or by invasion into
mucous membrane.
Large current passing through the skin - a small proportion may pass through the heart
Macroshock has the potential for both burns and cardiac arrhythmias. Currents pass through the
extremities mostly through the muscles. A current flowing from arm to arm, or arm to leg, must pass
through the thorax. In the thorax the current is split between the chest wall and the great vessels,
which obviously deliver the current directly to the myocardium.

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Microshock
Microshock is an electric shock risk that is present for hospital patients with externally protruding
intracardiac electrical conductors, such as external pacemaker electrodes, or saline filled catheters
Microshock refers to currents delivered directly to the heart via intracardiac electrodes or catheters.
Because the current is delivered to a very small area, only a very small current is required to reach
the fibrillation threshold.
Micro-shock" is an otherwise imperceptible electric current applied directly, or in very close
proximity, to the heart muscle of sufficient strength, frequency, and duration to cause disruption of
normal cardiac function.
The currently accepted minimum current is 10 A (microamps = 1/1000 of milliamps
Effect of frequency on neuro-muscular stimulation
The amount of current required to stimulate muscles is dependent on some range of frequency.
Referring to figure 1, it can be seen that the smallest current required to prevent the release of an
electrically live object occurs at a frequency of around 50 Hz. Above 10 kHz the neuro-muscular
response to current decreases almost exponentially.

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Burns
When an electric current passes through any substance having electrical resistance, heat is
produced. The amount of heat depends on the power dissipated (I2R).
Electrical burns often produce their most marked effects near to the skin.
Muscle cramps
When an electrical stimulus is applied to a motor nerve or a muscle, it contracts. The prolonged
involuntary contraction of muscles (tetanus) caused by an external electrical stimulus is
responsible for the phenomenon where a person who is holding an electrically live object can be
unable to let go (at frequency of 50 Hz, e.g. power supply).
Respiratory arrest
The muscles between the ribs (intercostal muscles)
need to repeatedly contract and relax in order to
facilitate breathing. Prolonged tetanus of these muscles
can therefore prevent breathing.
Cardiac arrest
The heart is a muscular organ, which needs to be able to contract and relax
repetitively in order to perform its function as a pump for the blood.
Tetanus of the heart musculature will prevent the pumping process.

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Ventricular fibrillation
Ventricular fibrillation can be triggered by very small electrical stimuli.
A current as low as 70 mA flowing from hand to hand across the chest, or 20 µA directly through
the heart may be sufficient.
It is for this reason that most deaths from electric shock are attributable to the occurrence of
ventricular fibrillation.
Natural protection factors
Reflex and automatic contraction of muscles on receiving an electrical stimulus often acts to
disconnect the person from the source of the stimulus.
A patient under anesthesia is relatively unprotected by these reflex mechanisms.
Normally, the skin has a high electrical resistance compared to the moist body tissues below,
and hence serves to reduce the amount of current that would otherwise flow.
A patient skin resistance may have been lowered in order to allow good connections of
monitoring electrodes to be made or, in the case of a patient undergoing surgery, there may
be no skin present in the current path.
The absence of natural protection factors as described above highlights the need for stringent
electrical safety specifications for medical electrical equipment and for routine test and
inspection regimes aimed at verifying electrical safety

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ELECTRICAL SAFETY TESTING
Why do we do electrical safety .?
√ Ensure patient safety
Protect against macroshock
Protect against microshock
√ Test for electrical internal breakdown / damage to power cord, AC mains feed,
etc.
√ Meet codes & standards
AAMI, IEC, UL, NFPA, etc.
√ Protect against legal liability
In case of a patient incident
Terminologies of EST
 Classes and Types
 L1 - Hot
 L2 - Neutral
 Earth - Ground
 Mains Line - Voltage
 Enclosure/Case - Chassis
 Protective Earth -Ground Wire
 Earth Leakage Current Leakage in Ground Wire
 Enclosure Leakage - Chassis Leakage
 Patient Leakage - Lead Leakage
 Patient Auxiliary - Leakage between Patient Leads
 Mains on Applied Parts - Lead Isolation
 Insulation Resistance - Dielectric Strength or Insulation Resistance between Hot and
Neutral to Ground
 Earth Resistance - Ground Wire Resistance

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Applied Parts -
A part of the equipment which in normal use:
Necessarily comes into physical contact with the patient for the equipment to perform its
function; or can be brought into contact with the patient; or needs to be touched by the patient
Accessible Part
Part of equipment which can be touched without the use of a tool.
• EXAMPLE 1: Illuminated push-buttons
• EXAMPLE 2: Indicator lamps
• EXAMPLE 3: Recorder pens
• EXAMPLE 4 : Parts of plug-in modules
• EXAMPLE 5: Batteries
Leakage currents
Current that is not functional.
Several different leakage currents are defined according to the paths that the currents take.
• Earth Leakage Current
• Enclosure Leakage Current
• Patient Leakage Current
• Patient auxiliary current
Causes of Leakage currents
If any conductor is raised to a potential above that of earth, some current is bound to flow from that
conductor to earth. The amount of current that flows depends on:
1- the voltage on the conductor.
2- the capacitive reactance between the conductor and earth.
3-the resistance between the conductor and earth.

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DRIFT
As components age and equipment undergoes changes in temperature or humidity or sustains
mechanical stress, performance gradually degrades. This is called drift. When this happens your
test results become unreliable and both design and performance quality suffers.
While drift cannot be eliminated, it can be detected and either corrected or
compensated for through the process of calibrationLeakage Current
Calibration: process of comparing an unknown against a reference standard within defined
limits, accuracies and Uncertainties
Verification: process of comparing an unknown against a reference standard at usually one
MEDICAL EQUIPMENT CLASS & TYPE
Equipment Class {I, II, III} - method of protection against electric shock
Equipment Type {B, BF, CF} - degree of protection
CLASSES MEDICAL ELECTRICAL EQUIPMENT
All electrical equipment is categorised into classes according to the method of protection
against electric shock that is used. For mains powered electrical equipment there are usually
two levels of protection used, called "basic" and "supplementary" protection. The
supplementary protection is intended to come into play in the event of failure of the basic
protection.
CLASS I - (Protection relying on fault currents to Earth)
Class I equipment has a protective earth. The basic means of protection is the insulation between
live parts and exposed conductive parts such as the metal enclosure. In the event of a fault that
would otherwise cause an exposed conductive part to become live, the supplementary protection
(i.e. the protective earth) comes into effect.
Class I equipment is fitted with a three core mains cable containing a protective earth wire.
Exposed metal parts on class I equipment are connected to this earth wire
Fault Current means the electrical current that flows through a circuit during an electrical fault
condition. A fault condition occurs when one or more electrical conductors contact ground and/or
each other. Types of faults include phase to ground, double-phase to ground, three-phase to
ground, phase-to-phase, and three-phase. A Fault Current is several times larger in magnitude

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than the current that normally flows through a circuit.
Class I medical electrical equipment should have fuses at the equipment end of the mains supply
lead in both the live and neutral conductors, so that the supplementary protection is operative
when the equipment is connected to an incorrectly wired socket outlet.
that appears to be plastic does not necessarily indicate that the equipment is not class I. There is
no agreed symbol in use to indicate that equipment is class I.
may be seen on medical electrical equipment adjacent to terminals.
CLASS II
The method of protection against electric shock in the case of class II equipment is either double
insulation or reinforced insulation. In double insulated equipment the basic protection is afforded
by the first layer of insulation. If the basic protection fails then supplementary protection is
provided by a second layer of insulation preventing contact with live parts.
Reinforced insulation is defined in standards as being a
single layer of insulation offering the same degree of
protection as double insulation.
Class II medical electrical equipment should be fused at the
equipment end of the supply lead in either mains conductor or in
both conductors if the equipment has a functional earth.
The symbol for class II equipment is two concentric squares indicating double insulation as
shown.
CLASS III
Class III equipment is defined in some equipment standards as that in which protection against
electric shock relies on the fact that no voltages higher than safety extra low voltage (SELV) are
present. SELV is defined in turn in the relevant standard as a voltage not exceeding 25V ac or 60V
dc. In practice such equipment is either battery operated or supplied by a SELV transformer.

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If battery operated equipment is capable of being operated when connected to the mains (for
example, for battery charging) then it must be safety tested as either class I or class II equipment.
Similarly, equipment powered from a SELV transformer should be tested in conjunction with the
transformer as class I or class II equipment as appropriate.
It is interesting to note that the current IEC standards relating to safety of medical electrical
equipment do not recognise Class III equipment since limitation of voltage is not deemed
sufficient to ensure safety of the patient. All medical electrical equipment that is capable of mains
connection must be classified as class I or class II. Medical electrical equipment having no mains
connection is simply referred to as "internally powered".
TYPES OF MEDICAL EQUIPMENTS
Each classification has differing requirements from the point of view of
Protection against electrical shock
As described above, the class of equipment defines the method of protection against electric
shock. The degree of protection for medical electrical equipment is defined by the type
designation. The reason for the existence of type designations is that different pieces of medical
electrical equipment have different areas of application and therefore different electrical safety
requirements.
For example, it would not be necessary to make a particular piece medical electrical equipment
safe enough for direct cardiac connection if there is no possibility of this situation arising.
All medical electrical equipment should be marked by the manufacturer with one of the type
symbols.
Type Symbol Definition
B
Equipment providing a particular degree of protection
against electric shock, particularly regarding allowable
leakage currents and reliability of the protective earth
connection (if present).
BF
As type B but with isolated or floating (F - type) applied
part or parts.
CF
Equipment providing a higher degree of protection against
electric shock than type BF, particularly with regard to
allowable leakage currents, and having floating applied
parts.

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INTERNATIONAL ELECTROTECHNICAL COMMISSION
The International Electrotechnical commission (IEC) is a non-profit, non-governmental
international standards organization that prepares and publishes International Standards for all
electrical, electronic and related technologies – collectively known as "electro technology".
IEC 60601-1
IEC 60601, “Medical Electrical Equipment—General Requirements for Safety” was introduced in
1977 and put forth a set of requirements for the manufacturers of medical equipment. These
requirements were designed to detect and eradicate any potential electric hazards presented by
the equipment being produced (e.g. leakage currents, protective grounding, etc.). Assuming the
equipment was utilized properly for the duration of its lifespan, these tests were meant to curb
possible defects later on. They were further utilized on equipment already in service as a means
of routine tests and after repair tests; however, this practice presented some unforeseen
difficulties. For example, IEC 60601 outlines type-testing in laboratory conditions, but often those
conditions are not available or applicable once the device is already in use
60601 is a widely accepted benchmark for medical electrical equipment and compliance with
IEC60601-1 has become a requirement for the commercialization of electrical medical equipment
in many countries. Many companies view compliance with IEC 60601-1 as a requirement for most
markets
• Design and Type-Test standard (Mandatory)
• Electrical and Mechanical Safety and Compliance of Medical Electronic Equipment
• Ensure Safety of Patient / User and Environment
IEC 60601-1 (type) Tests
• Earth Bond Test (high current)
• Insulation Test
• Leakage Tests (SFC’s)
o Earth
o Enclosure / Touch
o Patient (AC / DC)
o Patient Auxiliary (AC / DC)
o Patient type F
Warning : These tests are aimed to stress the equipment and can be destructive
IEC 62353

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IEC 62353, “Medical Electrical Equipment—Recurrent Test and Test After Repair of Medical
Electrical Equipment” emerged to accommodate the needs of in-service devices.
IEC 62353 is specifically designed around testing equipment in the field, and is therefore more
practical, more effective, and safer than using IEC 60601 in those particular circumstances.
• World wide validation of the new standard the 16 march 2007.
• Has been published, world wide, the 15th of May 2007.
• Has been published in France in March 2008, Italy in early 2009. Etc...
IEC 62353 Application area
It’s a standard designed for the field:
• Applicable to all the Medical devices and Systems, before the first use, during the
maintenance, inspection, regular tests and tests after repair.
• Not Mandatory
• Not a replacement of IEC 60601-1-1
• Not a replacement of Local Standard
• Does not describe Mechanical Safety
• Does not describe Electro Magnetic Compatibility
IEC 62353 Tests
• Earth Bond Test
• Insulation Test
• Leakage Test
Equipement
Direct, 2 modes (OE, ROE)
Alternative, 1 mode
Differential, 2 modes (Nor,Rev)
Applied Part
Direct 2 modes (Nor, Rev)
Alternative

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How is testing performed?
Before testing, accompanying documentation must be examined, and accordingly,
manufacturer recommendations of maintenance and repair taken into account. Whenever
and wherever possible, the device must be disconnected from the mains supply power;
otherwise, special measures must be implemented for the prevention of hazards resulting
from working on live devices.
Documentation
All tests carried out must be documented in depth. Testing documents must at the very least
contain the following entries:
 Designation of the test location (e.g. company, department, authority)
 Name of the person(s) who performed and evaluated the test
 Designation of the tested device and accessories (e.g. type, serial number, inventory
number)
 Executed tests including measured values, measuring methods and utilized measuring
instruments
 Function test

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 Final evaluation
 Date and ignature of the person who prepared the evaluation
 Identification of the tested device (if required by the operating service provider)
The methods of measurement used before initial start-up and the results of those
measurements should be documented for the purpose of comparison with the results of later
measurements. This comparison is recommended if the measured value amounts to more
than 90% of the limit value. With regard to systems, initial start-up testing must be performed
every time the system is altered (such as modified configuration or replacement of
components), and the changes and new measurements must be documented as well.
Visual Inspection
This is a fairly easy and very effective portion of the procedure; the human eye must not be
forgotten as a crucial tool that an operator of testing has available. The legibility of safety-
relevant labeling is inspected, as well as the device’s compliance with the manufacturer’s
specifications.
Protective Conductor Resistance Measurement
Protective conductor resistance measurements are performed on Class I devices to ensure
that all accessible conductive parts (which, in the event of a fault, may become live) are
appropriately secured to the protective conductor terminal. All devices must conform to the
following protective conductor connection limit values:

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The resistance of the protective earth conductor ismeasuredbetweenthe earthpinonthe mainspluganda
protectivelyearthedpointonthe equipmentenclosure (see figure6).The readingshouldnotnormallyexceed
0.2Ω at any suchpoint.
Devices with a removable mains power cable (measurement
without mains power cable) 0.2 Ω
Devices including mains power cable 0.3 Ω
Mains power cable (all available mains power cables are tested) 0.1 Ω
Systems with multiple electrical outlets 0.5 Ω
Connector cables such as data transmission lines and functional earth cables may simulate
protective conductor connections, and should be disconnected if possible before testing is
started.
The disconnection of protective conductors is not called for with permanently connected
devices.
Insulation Tests
Insulation resistance is a helpful measurement to find insulation faults caused by dust,
wetness or pollution but the measurement may be forbidden by some manufacturers to avoid
damage on sensitive parts. Furthermore, there is no limit value specified in IEC 62353, but the
following values can serve as a reliable guideline:
HEI 95 and DB9801 recommended that for class I equipment
the insulation resistance be measured at the mains plug
between the live and neutral pins connected together and
the earth pin. Whereas HEI 95 recommended using a 500V
DC insulation tester, DB 9801 recommended the use of 350V
DC as the test voltage.
HEI 95 further recommended for class II equipment that the
insulation resistance be measured between all applied parts
connected together and any accessible conductive parts of the
equipment. The value should not normally be less than 50MΩ

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Leakage Current Measurement
Leakage current measurement requirements only apply universally to AC components; DC
leakage current measurements must be determined and explicitly expounded upon in
accompanying documentation by manufacturers (complying also with IEC 60601 DC limit
values).
The measured value must be corrected to the value which corresponds to the measurement
at nominal line voltage.
 Current that is not functional.
 several different leakage currents are defined according to the paths that the currents take.
 Earth Leakage Current
 Enclosure Leakage Current
 Patient Leakage Current
 Patient auxiliary current
The following leakage currents are measured:
EARTH LEAKAGE CURRENT
current flowing from the MAINS PART through or across the insulation into the PROTECTIVE
EARTH CONDUCTOR
Under normal conditions, a person who is in contact with the earthed metal enclosure of the
equipment and with another earthed object would suffer no adverse effects even if a fairly
large earth leakage current were to flow. This is because the impedance to earth from the
enclosure is much lower through the protective earth conductor than it is through the person.
However, if the protective earth conductor becomes open circuited, then the situation
changes. Now, if the impedance between the transformer primary and the enclosure is of the
same order of magnitude as the impedance between the enclosure and earth through the
person, a shock hazard exists.
Protection
class I
(LN to PE)
Protection class II
(LN to accessible conductive part or
type BF application part)
(LN to type CF
application part)
2 MΩ 7 MΩ 70 MΩ

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Enclosure leakage current /Touch current
 LEAKAGE CURRENT flowing from the ENCLOSURE to earth or to another part of the
ENCLOSURE through a conductor other than the protective earth conductor.
Patient leakage current
 Patient leakage current is the leakage current that flows through a patient connected to an
applied part or parts.
 It can either flow from the applied parts via the patient to earth or from an external source of
high potential via the patient and the applied parts to earth.
Patient auxiliary current
 The patient auxiliary current is defined as the current that normally flows between parts of
the applied part through the patient, which is not intended to produce a physiological effect

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Device Leakage
Current
Device
Leakage
Current
(Continued)
Device leakage current is the sum of all possible leakage currents which
could flow over the user or the patient in the event of an interrupted
protective earth conductor. (For this reason, current in the protective
conductor, as well as from the application parts and accessible
conductive parts, must be acquired during measurement.)
In the IEC 60601-1 standard, this measurement corresponds to earth
leakage current with grounded application parts and housing
components.
In the case of protection class II devices, current corresponds to contact
current.
This leakage current will be designated housing leakage current in the
second edition of IEC 60601-1.

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Leakage Current
from the
Application
Part
Testing is only performed on type F application parts.
(Testing is usually not required for type B application parts, because it’s
included in device leakage current. However, the manufacturer may
require an additional leakage current measurement for type B
application parts.) Depending upon device layout, testing can be
performed by means of direct measurement (mains to application part)
or alternative measurement.
If alternative measurement is used, test voltage equal to nominal line
voltage is applied between the application part to be measured and all
mains power cables which are connected to each other (L, N and PE).
In the case of direct measurement, test voltage equal to nominal line
voltage is applied between the application part to be measured and PE
while the test object is being supplied with power from the mains.
Application parts of identical type can be connected to each other
during measurement, or the manufacturer’s instructions must be
followed. If different application parts are included, they must be
connected and measured individually, one after the other. Application
parts which are not included in the measurement are not connected.
This leakage current will also be designated “patient leakage current
with
single fault condition mains on application part in IEC 60601.
On some equipment it is required to measure patient leakage current
on Type B applicatrion parts according to IEC 60601. This current is
measured from the application part to ground and DC components will
also be taken into consideration.
Permissible Values for Leakage Current Measurements:
Device Leakage Current
Direct or differential measurement:
alternative measurement:
At protection
class I parts
0.5 mA
1.0 mA
At protection
class II parts
0.1 mA
0.5 mA
Leakage Current from the Application Part
Type BF:
Type CF:
5.0 mA
0.05 mA
Patient leakage current according to IEC
60601 Type B, BF or CF (normal condition) 0.1 mA

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Because cables and wiring (such as mains power cables, measurement cables, and data
transmission lines) have an enormous influence on the leakage current measurements, they
must be arranged in such a way as to minimize their interference.
Permanently connected devices need not be tested for leakage current measurements if the
location is in accordance with IEC 60364-7-710 (“Medical locations”), and is regular tested
according to this standard.
The following table summarizes the leakage current limits (in mA) specified by IEC60601-1
(second edition)
There are three methods to choose from for measuring leakage current; selection of which
should be based on the design of the device:
Alternative
method
Cannot be used for devices for which insulation in the power pack is not
included in the measurement (e.g. due to a relay which is only closed in the
operating state).
If the measured value resulting from equivalent measurement exceeds
5 mA
during testing of 3-phase devices, the test must be performed using the
direct or differential method.
Direct method
Cannot be used in IG (Isolated Ground) systems.
This method may not be used if the device under test cannot be isolated
from ground.
The protective conductor is interrupted when this measuring method is
used, for which reason it’s essential not to come into contact with
accessible conductive parts during testing, because danger of electrical
shock would
otherwise exist.

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Differential
Current
method
Cannot be used in IG systems.
Measuring instrument specifications must be observed when measuring
small leakage currents with this method. As a rule, the method is only
conditionally suitable for current values of less than 100 µA.
Function Test
Function tests regarding safety will be specified by the manufacturer, and should be executed
accordingly.
Function tests also fall under “essential performance characteristics” and “special
requirements” of IEC 60601. Most of the time, additional test instruments will be required
(such as with infusion pumps and defibrillators).
Restoration to Operable State
Once testing is complete, the device must be restored to an operable state.
This includes reconnection of power cables, data transmission lines and alarm devices, and
general setup, etc., so that the device is in the same state as it was prior to the testing.

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Conclusion
The Electrical Safety Tests and the standards are designed to protect us from the natural
proclivity of complex systems to eventually go awry.
Adherence to these is a crucial element in the operation of these electrical medical devices. At
the end of the day, all of this testing and these standards are not about product quality or
thoughtless conformity to mandated procedures; what it’s really about is what the whole
medical industry is about: The value of human health and safety.