This document provides an overview of electrical safety testing for medical equipment. It discusses the various classes and types of medical equipment and the electrical safety tests that should be performed on each. The key tests mentioned are protective earth continuity testing, insulation testing, and testing for earth leakage current and enclosure leakage current. Maintaining electrical safety is important to prevent electric shock to patients and users from medical equipment.

1. ELECTRICAL SAFETY
For
MEDICAL EQUIPMENT
By
Ismail Yusof

2. Electrical Safety – Medical Equipment
Contents:
1 Various Test Equipment used in Biomedical
Engineering
2 Introduction to Electrical Safety
3 Electricity - Physiological Effects
4 General Electrical Safety
5 Electricity – Leakage Current
6 Electrical Equipment – Classes and Types
7 Electrical Safety Tests

3. INTRODUCTION TO VARIOUS TEST
EQUIPMENT USED IN BIOMEDICAL
ENGINEERING

4. Workshop Tool & Equipment
Toolkit for general repair

5. Workshop Tool & Equipment
Insulation and Resistance Measuring Instrument, 1000 V, Digital

6. Workshop Tool & Equipment
Soldering Station
with temperature controller

7. Workshop Tool & Equipment
Analog Multimeter
Digital Multimeter

8. Test Instrument
Electrical Safety Analyser

9. Test Instrument
Electrical Safety Analyser

10. Test Instrument

11. Test Instrument
It measures delivered energy on its internal load.
The defibrillator pulse is stored and it can be viewed
via ECG output leads, paddles or scope output.

12. Test Instrument
Blood pressure simulator
that provides simulation
to test blood pressure monitors.

13. Test Instrument
The pulse oximeter testing method to simulate
the light absorption and arterial blood flow
of a human finger

14. Test Instrument
Power meter to service
the 1 MHz and 3 MHz therapy level
ultrasound generators.

15. Test Instrument
External pacemaker tester designed for
accurately testing all types of
external pacemaker.

16. Test Instrument

17. Test Instrument
ESU Analyser
Measure output power and RF leakage

18. Test Instrument
Infusion Pump Analyzer

19. SAFETY TESTERS
Safety Check
– Electrical Safety Tests (IEC 601)
– The basic purpose of safety testing in medical electrical
equipment is to be sure that a device is safe for the patient
and user. Such as:
• Grounding resistance of portable medical equipment
measured between equipment chassis and ground pin of
power plug shall not exceed 0.50 ohms.

20. ELECTRICAL
SAFETY

21. Biomedical Engineer-definition
• Biomedical Engineers assist in struggle
against illness and disease by providing
support for materials and tools that can be
utilized for diagnosis and treatment by
health care professionals.
• Biomedical Engineer have achieved this
position by assuming responsibility for
managing the safe use of medical
equipment within the hospital environment

22. A Historical Perspective
• Engineer’s first enter to clinical scene : late
1960s in response to concerns about
electrical safety of hospital patient
• Ralph Nader (consumer activist) : “at the very
least, 1200 Americans are electrocuted
annually during routine diagnostic and
therapeutic procedures in hospitals” Ladies
Home Journal, April 24, 1970
• Raise the level of concern about safe use of
medical device

23. A Historical Perspective
• Overnight growth of a new industry : hospital electrical
safety
• Joint Commission on the Accreditation of Hospital :
“hospital must inspect all equipment used on or near a
patient for electrical safety at least every 6 months”
• Hospital administrator’s options
– Paying medical device manufacturer
– Service contracting
– In-house staff

24. Safety Issue
• In USA, about 10,000 device-related
patient injuries each year
• Most injuries are attributable to improper
use of a device as a result of inadequate
training and lack of experience
• Medical personnel rarely read user
manuals until a problem occurred
• “Everything that can go wrong eventually
will go wrong” Murphy’s law

25. Electrical Shock
• Electric Shock : unwanted or
unnecessary physiological response to
current.
• Three phenomena :
– (1) electrical stimulation of excitable tissue
(nerve & muscle)
– (2) resistive heating of tissue, and
– (3) electrochemical burns and tissue damage

26. Electrical Safety
• Electric Safety is the best possible
limitation of hazardous electrical Macro –
and/or Microshocks, sustained by
patients, as well as explosion, fire or
damage to equipments and buildings.

27. Single Phase Power Supply
• The application of the safety testing on this training will
only apply to the Single Phase ( 3 wires ) 100 to 240 Volt
power supply.
• Any medical equipment use either 3 or 2 pins plug which
connected to the wall socket shall follow this electrical
safety procedure.

28. The IEC 601.1 Standard
 Several standard serve as ruling authority in
determine how medical equipment are to be
tested such UL, CSA, CE, TUV …
 The International Electro Technical
Commission’s IEC 601-1 standard is accepted
and implemented around the world.
 All this explanation will be based on IEC 601-1
Standard

29. The IEC 601.1 Standard

30. Medical Electrical Equipment
 Medical Electrical Equipment provided with no more than
one connection to a particular supply mains and
intended to;
1. Diagnose the patient,
2. Treat the patient,
3. Monitor the patient under medical supervision,
4. Makes physical or electrical contact with the patient ,
5. Transfers energy to or from the patient and/or detects
such energy transfer to or from patient.
The equipment includes those accessories as defined
by the manufacturer which are necessary to enable the
normal use of the equipment.

31. Safety of Medical Equipment
 The purpose of safety testing medical electronic
equipment is to ensure that a device is safe from
electrical hazards to patients, maintenance personnel's
and users.
 Electric shock are caused by electricity flowing through
the body after touching a damaged electrical device and
results muscle spasms, burns, cardiac and respiratory
arrest and Ventricular Fibrillation

32. Electrical Safety
• Electric safety in hospital is a shared
responsibility between several parties, in
addition to the physician, including:
• The nurses
• All engineers (electrical, biomedical, facility,
etc)
• Manufacturers
• The hospital

33. Electrical Safety – Critical Points
• The electrical installation, no matter how safe, is only
part of the safety requirements.
• Plugs and cords must be checked and rejected if
defective.
• Only devices tested for safety should be used.
• Electrical compatibility of the entire electrical system
must be tested regularly.
• Patients leads must be attached and connected
properly.
• Radio-frequency devices (including mobile
telephones) must be excluded.

34. Basic Safety
 Basic safety should be performed on line powered
before installation and after every repairs are;
– Ground wire integrity ( Resistance )
– Ground wire leakage
 The basic electrical characteristic usually cause the
most leakage currents in modern equipment is
Capacitive Reactance Coupling in power cord.
 The typical range of human body resistance with the
skin intact is 500 Ohm to 1,000 Ohm.
 The “let go” current of a shock is 14 mA in most
people.

35. Why Electrical Safety?
 Electrical safety NOT dependent on voltage but on
Leakage Current.
 At low voltage, leakage current flow through body
may be fatal to us.
 Patient may connected to several device
simultaneously . (ICU.)
 Patient may connected conductively with electronic
circuit. (ECG.)
 Contact directly to internal tissue. ( natural orifices
or break in the skin.)

36. Electricity - Physiological Effects
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 or VI). Whether or not the heat
produces a burn depends on the current
density.

37. Burns

38. Electricity - Physiological Effects
Muscle Cramps
When an electrical stimulus is applied to a
motor nerve or muscle, the muscle does exactly
what it is designed to do in the presence of such
a stimulus i.e. it contracts. The prolonged
involuntary contraction of muscles (tetanus)
caused by external electrical stimulus is
responsible for the phenomenon where a
person who is holding an electrically live object
can be unable to let go.

39. A muscle cramp is a painful, involuntary
muscle contraction.

40. Electricity - Physiological Effects
Respiratory Arrest
The muscles between the ribs (intercostal
muscles) need to repeatedly contract and relax
in order in order to facilitate breathing.
Prolonged tetanus of these muscles can
therefore prevent breathing.

41. Respiratory Arrest

42. Electricity - Physiological Effects
Cardiac Arrest
The heart is a muscular organ which needs to
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.

43. Cardiac Arrest

44. Electricity - Physiological Effects
Ventricular Fibrillation
The ventricles of the heart are the chambers
responsible for pumping blood out of the heart.
When the heart is in ventricular fibrillation, the
musculature of the ventricles undergoes irregular,
uncoordinated twitching resulting in no net blood
flow. The condition proves fatal if not corrected in
a very short space of time.

45. Ventricular fibrillation (VF) is a deadly arrhythmia.
In VF, the electrical signals that trigger the
heartbeat become very fast and chaotic in the
lower chambers of the heart. The heart no longer
can pump blood to the brain or body.

46. Electricity - Physiological Effects

47. Electricity - Physiological Effects

48. Electricity - Physiological Effects
Electrolysis
The movement of ions of opposite polarities in
opposite directions through a medium is called
electrolysis and can be made to occur be made to
occur by passing DC currents through body
tissues or fluids.

49. Electricity Conduction Mechanism
Charge carrier Charge carrier
e- skin e-
Charge carrier
ions
cell
wire(metal) wire(metal)
electrode(metal)
Tissue electrode(metal)
Electrolyte/Dielectric
Electrochemical Reactions

50. Important Susceptibility Parameters
For dog: 20A, human : 80~600 A
Safety limit : 10 A
Effect of entry point on current distribution

51. Macroshock
Hazards
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.

52. Microshock
Hazards
Electrically conducting devices
unintentionally make direct
contact with heart muscles,
ventricular fibrillation may be
induced by minute current (e.g.
200 uA) well below the threshold
of feeling.

53. General Electrical Safety

54. General Electrical Safety

55. General Electrical Safety

56. General Electrical Safety

57. General Electrical Safety

58. General Electrical Safety

59. General Electrical Safety

60. General Electrical Safety

61. Electricity - Leakage Currents
Leakage Currents
Current that is not functional. The following
leakage currents are defined: Earth Leakage
Current , Enclosure Leakage Current , and
Patient Leakage Current .
Earth Enclosure Patient
Leakage Leakage Leakage
Current Current Current

62. Electricity - Leakage Currents
Causes of leakage currents
If any conductor is raised to a potential above earth
potential, then some current is bound to flow from that
conductor to earth. This is true even of conductors that are
well insulated from earth, since there is no such thing as
perfect insulation or infinite resistance. The amount of
current that flows depends on:
• The voltage on the conductor
• The capacitive reactance between the conductor and
earth
• The resistance between the conductor and earth

63. Leakage
Current
Leakage current flows between
power supply wires and earth
ground within the rated value. In
case of the multiple operation,
however, the total leakage current
will be the sum of the leakage
current flows from each power
supply.

64. Electricity - Leakage Currents
Earth leakage current
Earth leakage current is the current which
normally flows in the earth conductor of a
protectively earthed piece of equipment.

65. Electricity - Leakage Currents

66. Electricity –
Enclosure Leakage Currents
Enclosure leakage current
Enclosure leakage current is described as
the current that flows from an exposed
conductive part of the conductor to earth
through a conductor other than the
protective earth conductor.

67. Electricity –
Enclosure Leakage Currents

68. Electricity –
Patient Leakage Current
Patient leakage current
Patient leakage current is the leakage current that
flows through a patient connected to an applied
part or parts.

69. Electricity –
Patient Leakage Current

70. Electricity –
Patient Auxiliary Current
Patient auxiliary current
The patient auxiliary current is defined as the
current which normally flows between parts of
the applied part through the patient which is not
intended to produce a physiological effect.

71. Electricity –
Patient Auxiliary Current

72. Electricity –
Class and Types of Equipment
Classes of Equipment
All electrical equipment is categorized into
classes according to the method of protection
against electric shock that is used.
Types of Equipment
The degree of protection for medical electrical
equipment is defined by the type designation.

73. Electricity –
Class of Equipment
Classes of Equipment
All electrical equipment is categorized into
classes according to the method of protection
against electric shock that is used.
CLASS I CLASS II
CLASS III

74. Electricity –
Class of Equipment
Class I equipment
Class 1 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 which would otherwise cause an
exposed conductive part to become live, the
supplementary protection (i.e. protective earth)
comes into effect.

75. General Electrical Safety

76. CLASS I EQUIPMENT

77. Electricity –
Class of Equipment
Class II equipment
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 basic
protection fails then supplementary protection is
afforded by a second layer of insulation
preventing contact with live parts.

78. Electricity –
Class of Equipment
Class II equipment
The symbol for class II equipment is 2
concentric squares indicating double
insulation as shown below.

79. General Electrical Safety

80. CLASS II EQUIPMENT

81. Electricity –
Class of Equipment
Class III equipment
Class III equipment is defined 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.

82. Electricity –
Types of Equipment
Types of Equipment
The degree of protection for medical
electrical equipment is defined by the type
designation.
Type B Type BF Type CF

83. Electricity –
Types of Equipment
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.

84. Electrical Safety Tests
Normal Condition
A basic principle behind the philosophy of
electrical safety is that in the event of a
single abnormal external condition arising
or of the failure of a single means of
protection against a hazard, no safety
hazard should arise.

85. Electrical Safety Tests
Single Fault Condition
Condition in which a single means of
electrical safety protection is defective or
an abnormal condition is present.
Examples of a single fault condition would
be interruption of the ground conductor on
a Class I equipment or opening of the
neutral supply conductor to the
equipment.

86. Electrical Safety Tests
Single Fault Condition

87. Protective Earth Continuity
Applicable to Class1, all types
Limit 0.2 ohms

88. Insulation Tests
Applicable to Class 1, all types
Limit Not less than 50Mohms

89. Insulation Tests
Applicable to Class II, all types
having applied parts
Limit : > 50 MOhms

90. Earth Leakage Current
Applicable to: Class 1 equipment all types
Limits: 0.5mA in NC, 1mA in SFC or 5mA and 10mA
respectively for permanently installed equipment

91. Enclosure Leakage Current
Applicable to Class 1 and class II
equipment , all types.
Limit0.1mA in NC, 0.5mA in SFC

92. Patient Leakage Current
Applicable to All Classes B and BF
equipment having applied parts
Limits 0.1mA in NC, 0.5mA in SFC

93. Patient Auxiliary Current
Applicable to All equipment having
applied parts.
Limits 0.1mA in NC, 0.5mA in SFC

94. Mains on Applied Parts
Applicable to Class 1 and class II
equipment , types BF&CF equipment having
applied parts.
Limits BF 5mA; CF 0.05mA per electrode

95. Safety Test as done by
BEMS

96. Electrical Safety Review
Electrical Safety and the Patients Depends on
Three Things: -
• An alert, caring, knowledgeable person
• Properly maintained, and applied equipment
• Proper grounding or double insulation of line-
powered equipment

97. Electrical Safety Review
Report, tag, and do not use equipment with:
• Frayed wires or cracked insulation
• Damaged plugs or missing ground prongs

98. Electrical Safety Review
Report, tag, and do not use receptacles with:
• Only two slots
• Missing cover plates
• Loose mountings
• Weak gripping force

99. Electrical Safety
Review
Inspections of Equipment: -
• Check of Strain-Relief

100. Electrical Safety Review
Avoid:
• Using cheaters (three-prong adapters)
• Using extension cords
• Placing liquids on electrical equipment
• Pulling plugs out of receptacles by the cord
• Rolling equipment over power cords
• Using defective equipment or receptacles
• Using equipment that sparks, smokes, or shocks

101. Electrical Safety Review
Be sure that users know how to use equipment
properly. Also be sure to:
• Check that line-powered equipment has three-
wire grounding cords, unless device is double
insulated
• Ask for help and instruction when needed
• Report defective equipment and receptacles

102. Electrical Safety Review
 Always use your common sense
 Do not end up like this person!

103. ELECTRICAL SAFETY
THE END
THANK YOU

104. Thank You