Electrical Safety Testing

1
Electrical Safety Testing
The Royal Liverpool and Broadgreen University
Hospitals
NHS Trust
Clinical
NHS
Engineering

• Azzam Taktak
• Clinical Engineering
• Royal Liverpool University Hospital
• Liverpool L7 8XP
• Email afgt_at_liv.ac.uk

2
Clinical Engineering Department
3
The Liverpool Safety Tester 1973
4
Program

• Standards and guidance documents
• Physiological effects of electricity
• Electrical hazards
• Electrical safety testing
• Risk management

5
Quiz

• The IEC 60601-1 Standard describes
• Commissioning Tests
• Type Tests
• Routine Safety Tests
• Type Testing is
• testing the equipment to determine what Type
  applied part it has
• testing a single example for compliance
• comparing the performance of different models of
  the same type
• Which Bodies produce standards for Medical
  Electrical Equipment safety
• IPEM
• IET
• BSI
• MHRA
• IEC

6
Quiz (cont.)

• Earth Leakage Current is current that
• passes to earth through the operator
• passes to earth through the patient
• flows down the earth wire of the equipment
• any combination of the above
• Which of the following situations is NOT a fault
  condition
• external voltage on the applied part
• ingress of gas or fluid
• mains polarity reversed
• patient accidentally touching earth
• Muscle contraction due to mains current passing
  through skin occurs above roughly
• 1 A
• 100 mA
• 10 mA
• 1 mA
• 0.1 mA

7
Quiz (cont.)

• A statement in 60601-1 takes precedence over
  60601-2
• True
• False
• Death by electrocution of patients in UK
  hospitals occurs at
• 10 per year or more
• about 1 per year
• 1 per 10 years or less
• Transposed Earth and Neutral wires at the plug
  end
• will cause a fuse to blow
• will cause excessive Touch Current
• will cause excessive Earth Leakage Current
• Which of the following is NOT a Medical
  Electrical System
• a medical equipment connected to a PC via a
  serial link
• two pieces of medical equipment connected via a
  serial link
• two pieces of medical equipment connected to a
  multiple socket outlet
• two pieces of medical equipment connected to the
  same patient
• None of the above

8
Standards and Guidance Documents
9
The IEC 60601 Series of Standards
Standards and Guidance Documents

• To enable international trade by using a common
  set of Safety Requirements such Standards are
  termed HARMONISED STANDARDS
• To set out the requirements for the design and
  manufacture of Medical Electrical Equipment
  including test requirements, construction, rules
  for the user interface and labeling
• It says nothing about testing after sale

10
The IEC 60601 Series of Standards
Standards and Guidance Documents
Section 5.1 The tests described in this standard
are TYPE TESTS Section 3.135 TYPE TEST test
on a representative sample of the equipment with
the objective of determining if the equipment, as
designed and manufactured, can meet the
requirements of this standard
11
Part 2 60601-2 Particular Requirements
Standards and Guidance Documents
Particular Standards take priority over the
General Standard. For example the Particular
Standard for Surgical Diathermy will allow
Functional Currents through the patient greatly
in excess of allowable leakage currents Examples
60601-2-2 Surgical Diathermy 60601-2-4 Cardiac
Defibrillators 60601-2-16 Haemodialysis,
Haemofilteration 60601-2-39 Peritoneal
Dialysis
12
Guidance Documents
Standards and Guidance Documents

• MHRA Medical Electrical Installation Guidance
  (MEIGaN)
• BS 7671 IEE Wiring Regulations
• MHRA DB2006, Managing Medical Devices
• IPEM report 90 Safe Design and Construction of
  Medical Equipment
• IPEM report Electrical Safety Testing of Medical
  Equipment. In print

13
Physiological Effects of Electricity
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Physiological Effects of Electricity on the Body
Physiological Effects of Electricity

• Electrolysis (mainly near d.c.)
• Neuromuscular effects (mainly 10-100Hz)
• Heating (mainly 100KHz-30Mhz)

15
Neuromuscular Effects
Physiological Effects of Electricity
For a (15-100Hz) current passing between the
hands, the following effects are
expected 0.5-1mA Perception 10mA Cant let
go 100mA Severe pain. Interference with
breathing and heart function 1A Sustai
ned heart contraction
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Neuromuscular Effects
Physiological Effects of Electricity
Macroshock Large current passing through the
skin - a small proportion may pass through the
heart Microshock Current applied directly to
the heart (e.g. pacing leads, intracardiac
temperature/pressure lines).
17
Physiological Effects of Electricity
Heating Effects - Surgical Diathermy
In Surgical Diathermy the heat is concentrated at
the tip of the probe because the current density
(A/m2) is very high but at the plate it is low.
Heating will occur at the plate if the contact
area reduces (plate comes loose)
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Physiological Effects of Electricity
Electrolysis
The formation of sodium atoms at the negative
electrode and chlorine atoms at the positive
electrode causes local chemical actions which
kills the cells.
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Electrical Hazards
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Electrical Hazards
The UK Mains Supply is Earth Referenced The
substation transformer
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Electrical Hazards
Typical Voltages at the Wall Socket
Note the preferred method of handwiring plugs
Long earth wire, short live
Brown (Live) 240 volts to earth Blue (Neutral) 3
volts to earth (Opposite phase)
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Electrical Hazards
Typical Hazards in the plug
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Electrical Hazards
Leakage Current
In Class I equipment, most leakage current is
caused by capacitance between the leads in the
mains cord and a small amount due to stray
capacitance within the equipment itself.
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Electrical Hazards
Leakage Current
If the earth lead becomes detached, then the
current that would normally have flowed along it
will now be available on the case of the
equipment and, in the case of a Type B applied
part, it will also flow through the patient
25
Electrical Hazards
Standard Filter Circuit
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Electrical Hazards
Medical Filter Circuit
27
Electrical Hazards
Loss of Earth in Class 1 Equipment
This is the most common and most serious hazard
since a simple failure of basic insulation will
then produce a deadly situation of the metal case
being at live mains voltage
Loss of earth will only be found by testing
28
Multiple Socket Outlets (MSO)
Electrical Hazards
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Multiple Socket Outlets (MSO)
Electrical Hazards
Risk with using domestic types
30
Connecting Medical with Non-Medical Equipment
Electrical Hazards
The medical equipment might draw large currents
via the I/O port which, under a SFC, could appear
on the applied part (Type B) or on the enclosure
for Class I
31
Connecting Medical with Non-Medical Equipment
Electrical Hazards
In case of an interruption of protective earthing
for an equipment in the patient environment, this
potential difference may appear on the enclosure
of the equipment causing a safety hazard for the
operator or for the patient
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Incidents of Electrocution in Hospitals
Electrical Hazards

• Humidity in the plugs of blood and fluid heaters
  causing device failure (Andersen C, Pold R,
  Nielsen HD. Ugeskr Laeger 2000 162(6))
• Accidental toppling of a fluid container causing
  spillage onto a blood pressure monitor (Singleton
  RJ, Ludbrook GL, Webb RK, Fox MA. Anaesth
  Intensive Care 1993 21(5))
• Electric shocks to anaesthetists after touching a
  faulty device and the chassis of another device
  simultaneously (Singleton RJ, Ludbrook GL, Webb
  RK, Fox MA. Anaesth Intensive Care 1993 21(5))

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Incidents of Electrocution in Hospitals
Electrical Hazards

• An anaesthetised patient was connected to an ECG
  device that had been wired wrongly with the earth
  and neutral connections transposed. After
  noticing electrical interference with the ECG
  signal, the anaesthetist instructed an assistant
  to plug the monitor into a 2nd wall socket.
  Unknown to the assistant, the 2nd socket was
  wired with reverse polarity causing the chassis
  of the monitor to go live and suffered a minor
  shock. Unfortunately the patient experienced an
  intense shock since she was also connected to a
  surgical diathermy plate. She became cyanotic and
  her pulse stopped but later recovered completely
  (Atkin DH, Orkin LR. Anesthesiology 1973 38(2))

34
Incidents of Electrocution in Hospitals
Electrical Hazards

• A 9-month old baby was found dead on a bed after
  admission to hospital with suspected pneumonia.
  The patient apparently put an uncovered oval
  shaped lamp switch (pendant switch) into his
  mouth and died of electric shock after contacting
  the exposed wires (Yamazaki M, Bai H, Tun Z,
  Ogura Y, Wakasugi C. J Forensic Sci 1997 42(1))

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Electrical Safety Testing
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Web-Based Survey of EBME Departments
Electrical Safety Testing

• 80 of respondents (out of 26 replies in total)
  had uncovered at least one failure in the year
  2004 / 2005 through routine testing.
• Of these, approximately 30 could have caused a
  hazard to the patient or operator.
• 58 always test loan items
• 61 test domiciliary medical equipment
• 70 test systems (e.g. endoscope or anaesthetic
  trolleys)
• Half the respondents test once a year

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Electrical Safety Testing Procedure
Electrical Safety Testing
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Visual Inspection
Electrical Safety Testing
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Visual Inspection
Electrical Safety Testing

• For systems, inspection should include ensuring
  that the systems components are all labelled and
  have all been tested individually during
  acceptance testing. For routine testing, the
  tester should ensure that the system has not been
  re-configured or items substituted.
• For installations, visual inspection may include
• Electrical works test certificates
• Electrical safety certificate for installations
• MEIGaN test certificate for sockets wiring, earth
  wiring and equipotential bonding
• Review of suppliers EST
• Test certificates of other plug-in medical
  equipment or systems in the patient area

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Earth Resistance Test
Electrical Safety Testing
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Earth Resistance Test
Electrical Safety Testing
Plug-in equipment
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Earth Resistance Test
Electrical Safety Testing
Plug-in system
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Earth Resistance Test
Electrical Safety Testing
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Insulation Test
Electrical Safety Testing
45
Insulation Test
Electrical Safety Testing
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Insulation Test
Electrical Safety Testing
Equipment exhibiting values an order of magnitude
lower may be permissible, if they involve the
following

• hygroscopic mineral-insulated heating elements,
  which may exhibit low values until run for some
  hours to desiccate
• interference-suppression and discharge devices
  such as in Visual Display Units
• a compromise struck with competing requirements
  e.g. conductivity of operating theatre electrical
  warming mattress.

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Insulation Test
Electrical Safety Testing

• For a plugged-in system, it is worth doing a
  mains insulation test on the system as a whole to
  check the integrity of the interconnecting mains
  wiring and the MSO if fitted.
• For installations, this test is impractical and
  may be dangerous. If the test is to be performed,
  a number of preliminary steps are required. The
  equipment / system must be disconnected from the
  electrical supply. Allowance should be made for
  discharging large capacitors, which may hold
  considerable charge for some time after the
  machine is disconnected. Also any Uninterruptible
  Power Supplies (UPS) must be identified and
  disconnected.

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Leakage Current Test
Electrical Safety Testing
49
Leakage Current Test
Electrical Safety Testing
Plug-in equipment
50
Leakage Current Test
Electrical Safety Testing
MSO
SIP/SOP
MD
A (IEC 60601)
B (IEC XXXX)
MD
MD
Plug-in system
51
Leakage Current Test
Electrical Safety Testing
Incoming PE Conductor
lt 5 mA
DUT 1
MD
A
B
DUT 2
ERB
Installation
52
Leakage Current Test(Plug-in Equipment)
Electrical Safety Testing
53
Installations and Single Fault Conditions (SFCs)
Electrical Safety Testing

• The Standard specifies that open circuit of a
  Protective Earth Conductor of permanently
  installed equipment is not designated as a SFC
• Introducing faults on the system for test
  purposes may be hazardous to both tester and
  equipment because of the high power circuits in
  most fixed equipment systems
• Suppliers of such equipment will generally advise
  against SFC testing
• Many of the SFCs are not as significant a risk in
  fixed equipment as they are in other medical
  devices. Earth leads cannot be easily
  disconnected, and live or neutral wires do not
  easily detach. The electrical installer should
  ensure that there are no problems with phase
  reversal at commissioning.

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Special Cases

• Non-pacing and pacing defibrillators
• Lasers
• Short-Wave Diathermy (SWD)
• Bed-frames
• HF Surgery equipment (surgical diathermy
  generators)
• Cautery equipment
• Ultrasound equipment
• Mobile X-ray equipment
• Patient monitoring
• In-line or plug-top power supplies
• DC Inverters for pseudo-mains supply
• Ambulance trolleys
• Anaesthetic recording systems
• ITU centralised monitoring systems
• Cardiac Catheterisation Lab
• General Radiographic Room
• Magnetic Resonance Imaging System (MRI)
• Medical Linear Accelerator
• Whole Body PUVA Cabinet

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Frequency of Safety Tests
Electrical Safety Testing
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Risk Management
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Risk Management
Separation Transformers
58
Separation Transformers
Risk Management

• Class I
• The following are not required
• Maximum rated output power (1KVA)
• Maximum degree of protection (IPX4)
• Double or reinforced insulation
• Isolation monitoring is not required
• Protectively earthed centre tapped secondary
  winding is allowed

59
MSO/Transformer Assembly
Risk Management
60
MSO/Transformer Assembly
Risk Management
61
MSO/Transformer Assembly
Risk Management
62
Risk Management
Other Separation Devices
Some are available for common interfaces.
For Serial Ports
For ethernet networks
63
Connecting Medical with Non-Medical Equipment
Electrical Hazards
Make sure the I/O port is isolated from the
enclosure and the A/P. If it is not or if unsure
use an separation device
64
Connecting Medical with Non-Medical Equipment
Electrical Hazards
Always use a separation device
65
Risk Management
Residual Current Devices (RCDs)
These sense the difference between currents in
the live and neutral leads. If the difference
exceed a set level (usually 30mA for domestic
installations) a relay is operated to disconnect
the supply
RCD circuit
I live
N/C
L
Ferrite Ring
N/C
I Neutral
N
66
Risk Management
Residual Current Devices (RCDs)
RCD circuit
In normal circumstances I Live - I Neutral 0.
If any current does not return through the
Neutral lead then the supply is
disconnected. This will detect any of the faults
in the mains plug wiring.
I live
N/C
L
Ferrite Ring
N/C
I Neutral
N
67
Quiz

• The IEC 60601-1 Standard describes
• Commissioning Tests
• Type Tests
• Routine Safety Tests
• Type Testing is
• testing the equipment to determine what Type
  applied part it has
• testing a single example for compliance
• comparing the performance of different models of
  the same type
• Which Bodies produce standards for Medical
  Electrical Equipment safety
• IPEM
• IET
• BSI
• MHRA
• IEC

68
Quiz

• The IEC 60601-1 Standard describes
• Commissioning Tests
• Type Tests
• Routine Safety Tests
• Type Testing is
• testing the equipment to determine what Type
  applied part it has
• testing a single example for compliance
• comparing the performance of different models of
  the same type
• Which Bodies produce standards for Medical
  Electrical Equipment safety
• IPEM
• IET
• BSI
• MHRA
• IEC

69
Quiz

• The IEC 60601-1 Standard describes
• Commissioning Tests
• Type Tests
• Routine Safety Tests
• Type Testing is
• testing the equipment to determine what Type
  applied part it has
• testing a single example for compliance
• comparing the performance of different models of
  the same type
• Which Bodies produce standards for Medical
  Electrical Equipment safety
• IPEM
• IET
• BSI
• MHRA
• IEC

70
Quiz

• The IEC 60601-1 Standard describes
• Commissioning Tests
• Type Tests
• Routine Safety Tests
• Type Testing is
• testing the equipment to determine what Type
  applied part it has
• testing a single example for compliance
• comparing the performance of different models of
  the same type
• Which Bodies produce standards for Medical
  Electrical Equipment safety
• IPEM
• IET
• BSI
• MHRA
• IEC

71
Quiz (cont.)

• Earth Leakage Current is current that
• passes to earth through the operator
• passes to earth through the patient
• flows down the earth wire of the equipment
• any combination of the above
• Which of the following situations is NOT a fault
  condition
• external voltage on the applied part
• ingress of gas or fluid
• mains polarity reversed
• patient accidentally touching earth
• Muscle contraction due to mains current passing
  through skin occurs above roughly
• 1 A
• 100 mA
• 10 mA
• 1 mA
• 0.1 mA

72
Quiz (cont.)

• Earth Leakage Current is current that
• passes to earth through the operator
• passes to earth through the patient
• flows down the earth wire of the equipment
• any combination of the above
• Which of the following situations is NOT a fault
  condition
• external voltage on the applied part
• ingress of gas or fluid
• mains polarity reversed
• patient accidentally touching earth
• Muscle contraction due to mains current passing
  through skin occurs above roughly
• 1 A
• 100 mA
• 10 mA
• 1 mA
• 0.1 mA

73
Quiz (cont.)

• Earth Leakage Current is current that
• passes to earth through the operator
• passes to earth through the patient
• flows down the earth wire of the equipment
• any combination of the above
• Which of the following situations is NOT a fault
  condition
• external voltage on the applied part
• ingress of gas or fluid
• mains polarity reversed
• patient accidentally touching earth
• Muscle contraction due to mains current passing
  through skin occurs above roughly
• 1 A
• 100 mA
• 10 mA
• 1 mA
• 0.1 mA

74
Quiz (cont.)

• Earth Leakage Current is current that
• passes to earth through the operator
• passes to earth through the patient
• flows down the earth wire of the equipment
• any combination of the above
• Which of the following situations is NOT a fault
  condition
• external voltage on the applied part
• ingress of gas or fluid
• mains polarity reversed
• patient accidentally touching earth
• Muscle contraction due to mains current passing
  through skin occurs above roughly
• 1 A
• 100 mA
• 10 mA
• 1 mA
• 0.1 mA

75
Quiz (cont.)

• A statement in 60601-1 takes precedence over
  60601-2
• True
• False
• Death by electrocution of patients in UK
  hospitals occurs at
• 10 per year or more
• about 1 per year
• 1 per 10 years or less
• Transposed Earth and Neutral wires at the plug
  end
• will cause a fuse to blow
• will cause excessive Touch Current
• will cause excessive Earth Leakage Current
• Which of the following is NOT a Medical
  Electrical System
• a medical equipment connected to a PC via a
  serial link
• two pieces of medical equipment connected via a
  serial link
• two pieces of medical equipment connected to a
  multiple socket outlet
• two pieces of medical equipment connected to the
  same patient
• None of the above

76
Quiz (cont.)

• A statement in 60601-1 takes precedence over
  60601-2
• True
• False
• Death by electrocution of patients in UK
  hospitals occurs at
• 10 per year or more
• about 1 per year
• 1 per 10 years or less
• Transposed Earth and Neutral wires at the plug
  end
• will cause a fuse to blow
• will cause excessive Touch Current
• will cause excessive Earth Leakage Current
• Which of the following is NOT a Medical
  Electrical System
• a medical equipment connected to a PC via a
  serial link
• two pieces of medical equipment connected via a
  serial link
• two pieces of medical equipment connected to a
  multiple socket outlet
• two pieces of medical equipment connected to the
  same patient
• None of the above

77
Quiz (cont.)

• A statement in 60601-1 takes precedence over
  60601-2
• True
• False
• Death by electrocution of patients in UK
  hospitals occurs at
• 10 per year or more
• about 1 per year
• 1 per 10 years or less
• Transposed Earth and Neutral wires at the plug
  end
• will cause a fuse to blow
• will cause excessive Touch Current
• will cause excessive Earth Leakage Current
• Which of the following is NOT a Medical
  Electrical System
• a medical equipment connected to a PC via a
  serial link
• two pieces of medical equipment connected via a
  serial link
• two pieces of medical equipment connected to a
  multiple socket outlet
• two pieces of medical equipment connected to the
  same patient
• None of the above

78
Quiz (cont.)

• A statement in 60601-1 takes precedence over
  60601-2
• True
• False
• Death by electrocution of patients in UK
  hospitals occurs at
• 10 per year or more
• about 1 per year
• 1 per 10 years or less
• Transposed Earth and Neutral wires at the plug
  end
• will cause a fuse to blow
• will cause excessive Touch Current
• will cause excessive Earth Leakage Current
• Which of the following is NOT a Medical
  Electrical System
• a medical equipment connected to a PC via a
  serial link
• two pieces of medical equipment connected via a
  serial link
• two pieces of medical equipment connected to a
  multiple socket outlet
• two pieces of medical equipment connected to the
  same patient
• None of the above

79
Quiz (cont.)

• A statement in 60601-1 takes precedence over
  60601-2
• True
• False
• Death by electrocution of patients in UK
  hospitals occurs at
• 10 per year or more
• about 1 per year
• 1 per 10 years or less
• Transposed Earth and Neutral wires at the plug
  end
• will cause a fuse to blow
• will cause excessive Touch Current
• will cause excessive Earth Leakage Current
• Which of the following is NOT a Medical
  Electrical System
• a medical equipment connected to a PC via a
  serial link
• two pieces of medical equipment connected via a
  serial link
• two pieces of medical equipment connected to a
  multiple socket outlet
• two pieces of medical equipment connected to the
  same patient
• None of the above

80
Thank You