This document discusses safety and security related to electricity. It defines key terms related to physiological effects of electricity on the human body. It describes thresholds of perception, let-go, and ventricular fibrillation. It discusses main causes of electric shock and factors that influence injury seriousness. It also covers standards, best practices, and equipment for safety in electrical work including personal protective equipment, insulation, enclosures, overvoltage categories and more.

1. SAFETY AND
SECURITY
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2. PHYSIOLOGICAL
EFFECT OF THE
ELECTRICITY
PROTECTION OF PEOPLE
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Definitions
Internal impedance of the human body (Zi): Impedance between two
electrodes in contact with two parts of the human body, after removing
the skin from under the electrodes.
Impedance of the skin (Zp): Impedance between an electrode on the
skin and the conductive tissues underneath.
Total impedance of the human body (ZT): Vectorial sum of the
internal impedance and the impedances of the skin.
Initial resistance of the human body (Ri): Resistance limiting the
peak value of the current at the moment when the touch voltage occurs.

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Definitions
Threshold of perception: The minimum value of current which causes
any sensation for the person through which it is flowing.
Threshold of let-go: The maximum value of current at which a person
holding electrodes can let go of the electrodes.
Threshold of ventricular fibrillation: The minimum value of current
which causes ventricular fibrillation.

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Main causes are:
• Operating mode inappropriate or dangerous (31%),
• Lack of awareness of risks (30%),
• Incomplete application procedures (15%),
• Inadequate training (12%),
• The state of the material (12%),
• Soil conditions (11%)Type de contact
In average, 75 % of the Electric shock is from indirect contact, 20 %
from direct contact. Statistic shows that:
• 1/3 of lesions are in multiple places.
• Eyes, arms, hands are the most affected
• 60% of lesions are burns,
• 6 % of lesions are internal.
Main causes of Electric shock

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Seriousness factors
The level of injuries caused by the electric current is due to a
combination of several factors:
• The intensity of the current flowing through the human body,
• source of electrical energy (voltage, power) and the environment
(insulating or highly conductive)
• The duration of current flow through the human body,
• The surface area of contact,
• The particular susceptibility of the person subjected to the action of
electric current.
Main causes of Electric choc

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Value of the initial resistance of the human body (Ri)
Touch Voltage (V) Values for the total body impedance (Ω) that are not exceeded for a
percentage of (population)
5% 50% 95%
25 1750 3250 6100
50 1450 2625 4375
75 1250 2200 3500
100 1200 1875 3200
220 1000 1350 2125
700 750 1100 1550
1000 700 1050 1500

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Current through the body and effects
In AC

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In DC

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Direct – Indirect contact
Direct Contact Indirect Contact

13. VOLTAGE RANGE FROM IEC &
RISKS
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IEC voltage range AC DC Defining risk
High voltage
(supply system)
> 1000 Vrms > 1500 V electrical arcing
Low voltage
(supply system)
50–1000 Vrms 120–1500 V Electrical shock
Extra-low voltage
(supply system)
< 50 Vrms < 120 V Low risk

14. SAFETY
PROCEDURE IN
ELECTRICAL WORK
(STANDARDS AND BEST PRACTICES)
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15. PREVENT DIRECT CONTACTS
• Remoteness
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16. PREVENT DIRECT CONTACTS
• Obstacles • Insulation
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17. PREVENT INDIRECT CONTACT
By automatic
disconnection of
supply
• This principle consist
in connected to the
earth all metallic part
of equipment and
appliances. The
disconnection can be
done by MCB or
RCCB depending on
the earthing system.
Without automatic
disconnection of
the supply
• This can be done by
three ways:
• Class II
equipment
• Isolated circuits
• Very low voltage
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18. EQUIPMENT CLASSIFICATION
Class 0
• These appliances have
no protective-earth
connection and feature
only a single level of
insulation and were
intended for use in dry
areas.
Class 1
• These appliances must
have their chassis
connected to electrical
earth . The earth
connection is achieved
with a 3-conductor
mains cable.
Class 2
• A Class II or double insulated
electrical appliance is one
which has been designed in
such a way that it does not
require a safety connection to
electrical earth (ground).
Class 3
• A Class III appliance is
designed to be supplied from
a separated/safety extra-low
voltage (SELV) power source.
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19. IP CODE (IEC.60529.2001)
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The IP Code, International Protection Marking (IEC 60529), classifies
and rates the degree of protection provided against the intrusion
(including body parts such as hands and fingers), dust, accidental
contact, and water by mechanical casings and electrical enclosures.
The standard aims to provide users more detailed information than
vague marketing terms such as waterproof. The digits (characteristic
numerals) indicate conformity with the conditions summarized in the
tables below. Where there is no protection rating with regard to one of
the criteria, the digit is replaced with the letter X.

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21. IK CODE DEFINITION
Standard IEC 62262 defines an IK code that characterises the
aptitude of equipment to resist mechanical impacts on all sides.
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22. OVERVOLTAGE CATEGORIES
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Overvoltage categories classification of live electric circuits is used in
measurement and testing of installations and equipment, usually in the
relation within a building (residential or industrial)
There are four categories designated by a mark such as “CAT III, 150 V"
or "CAT IV, 1000 V".
• CAT I is applicable to instruments and equipment, which are not
intended to be connected to the mains supply
• CAT II defines circuits which are intended for direct connection into
mains sockets or similar points.
• CAT III is for circuits which can be connected to the mains installation
of a building
• CAT IV includes circuits which are connected directly to the source of
power for a given building.

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Rated Voltage IEC 61010-1 2nd Edition
CAT IV CAT III CAT II
150V 4,000V 2,500V 1,500V
300V 6,000V 4,000V 2,500V
600V 8,000V 6,000V 4,000V
1,000V 12,000V 8,000V 6,000V
Resistance 2 ohms 2 ohms 12 ohms
In addition to the label “CAT”, the maximum voltage must
be marked. This voltage is the maximum voltage between
live and ground of the circuit or the same overvoltage
range.

25. SECURITY EQUIPMENT
Personal protective equipment (PPE)
• safety glasses
• face shields
• hard insulated hats
• safety isolated shoes
• insulating (rubber) gloves with leather protectors
• insulating sleeves
• flame-resistant (FR) clothing
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26. Insulating Protective Equipment (IPE)
• Insulating mat
• Insulating tools
• Insulating ladder
• Insulating pole
• Insulating stool
• voltage detector
• temporary-grounding and temporary-short-circuit set
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28. Collective protective equipment
• Protective screen
• Poles, chains
• Warning board and sign
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29. MEASURING DEVICES
The measuring device should:
• Have an insulating case
• Be Class II
• Have an IP2X
• Have the right measurement category.
Accessories should have the same
characteristics
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31. Zone 1: Non vicinity
Zone 4: Vicinity area in LV (less than 30 cm from live
parts). All equipment with IP < IP2X is considered as live
part.
Zone 2: Vicinity area in HV (up to red line)
• 2 m (79 in) if U < 50 000 V (3 m -118 In – for
aerial wire)
• 3 m (118 in) if U < 250 000 V (5 m -197 In – for
aerial wire)
• 4 m (157 in) if U < 400 000 V (5 m -197 In – for
aerial wire)
• 5 m (197 in) if U < 750 000 V (5 m -197 In – for
aerial wire)
Zone 3 : This is the distance between the live part and
the Minimum Distance Approach (MDA). In this area
there a risk of electric arc. The MDA distance is 60 cm (24
in) up to 50 000 V. From 50 000 V the MDA is given by the
following formula: MDA(m) = 0,005 x U(kV) + 0,5
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32. THE PADLOCKING
This the duty of the holder of BC / HC Electrical
Authorization
He does or supervises the padlocking
He is responsible of the disconnection of the
equipment from the power supply and the lock of the
switch disconnector.
He his establishing the acknowledgment of
padlocking. (work permit delivred)
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33. FIVE STEPS
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Acknowledgment
should be signed
2- Lock
1- Disconnect
3- Identify the equipment
4- Doing the Voltage
checking and the earthing

34. FIRST STEP: DISCONNECTION
Switch disconnector
Sockets
Withdraw fuse
Plug devices
Control, protecting devices
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35. SECOND STEP: EQUIPMENT
LOCK
Label and lock device
On LV equipment, Board
with « Equipment lockout –
Don not Manoeuvre »
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36. THIRD STEP: IDENTIFICATION
Identify the place of the
equipment
Reading charts and circuit
diagram
Reading of labels and board
Visual identification
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37. FOURTH STEP: VOLTAGE
CHECKING
The voltage checking is
carried out close to the
working place
The earthing and short
circuiting should be done on
both part of the circuit.
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38. FIRTH STEP: MARK WORKING
PLACE
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39. PROTECTIVE
DEVICES
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40. CIRCUIT BREAKER
A circuit breaker is composed
• magnetic relay
• thermal relay.
It protect against overload and short circuit.
Low-voltage (less than 1,000 VAC) types :
• MCB (Miniature Circuit Breaker) — rated current not more than
100 A.
• MCCB (Molded Case Circuit Breaker)—rated current up to
2,500 A,
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41. CIRCUIT BREAKER
The characteristics of low-voltage circuit breakers are
given by international standards such as IEC 947. These
circuit breakers are often installed in draw-out
enclosures that allow removal and interchange without
dismantling the switchgear.
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42. CIRCUIT BREAKER
Inside of a circuit breaker
• The DIN rail-mounted thermal-
magnetic miniature circuit breaker is
the most common style. The design
includes the following components:
• 1-Actuator lever
• 2-Actuator mechanism
• 3-Contacts
• 4-Terminals
• 5-Bimetallic strip.
• 6-Calibration screw
• 7-Solenoid
• 8-Arc divider/extinguisher
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43. CIRCUIT
BREAKER
Operating
principle
(MCB/MCCB)
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44. CURVES OF CIRCUIT BREAKER
(MCCB/MCB)
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Type Trip Protection Example of uses
B 3.2 to 4,8 In
Generators, people in TN
and IT earthing system with
long cables (no peak
current)
C 7 to 10 In Cables General uses
D 10 to 14 In
Circuit and load with High
inrush current
Motors
Transformer

45. CURVES OF CIRCUIT BREAKER
(MCCB/MCB)
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Type Trip Protection Example of uses
K 10 to 14 In
Circuit and load with High
inrush current
Motors
Transformer
Auxiliary circuit
Z 2.4 to 3.6 In Electronics
Diodes
Thyristors
MA 12 In
Motor (without thermal
relay)
Starters
Motors

46. 6.5.TRIPPING CURVES
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47. RCD (RESIDUAL CURRENT
DEVICE) / ELCB (EARTH
LEAKAGE CIRCUIT BREAKER)
The RCD / ELCB has been created to measure the
current going through the lives and the neutral. If the
sum of this current is not zero, this means that there
is a leakage usually to the earth wire and the ground.
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48. RCD / ELCB
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49. TYPE OF RCCD
The design of RCD and ELCB are different depending of the
circuit.
• Industrial type circuit-breakers with integrated or adaptable
RCD module
• Household and similar miniature circuit-breakers with RCD
• Residual current circuit-breakers and RCDs with separate toroid
current transformer
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50. GROUNDING
SYSTEMS
(BASICS - STANDARDS)
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51. EMERGENCE OF EARTHING
SYSTEMS
Today the 3 system earthing such as defined in IEC 60364
and French standard NF C 15-100, are:
• Earthed neutral –TT (Terre-Terre)
• Exposed-conductive parts connected to neutral –TN (Terre-
Neutre)
• Unearthed (or impedance-earthed) neutral –IT (Isolé-Terre)
Those three earthing systems are created to ensure the
protection of persons and property
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52. 52
The combination of these two letters gives
three possible configurations

53. EARTHED NEUTRAL –
TT
In Earthed Neutral (TT) System,
• the neutral from the main transformer is connected to the ground
• All metallic parts of the equipment and loads are connected to
another earth ground.
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54. EXPOSED-CONDUCTIVE
PARTS CONNECTED TO
NEUTRAL –TN
the neutral from the transformer is connected to the earth ground
All metallic part of the equipment are connected to the neutral.
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 There are two ways to connect the metallic part to
the neutral:
 Through an earth wire connected to the neutral (TN-S)
 connected directly to the neutral (TN-C).
 An electric fault becomes a short circuit and circuit
breaker or fuse will open the circuit.
 This system has to be well design to be sure of
the efficiency of the security.

55. TN-S
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56. TN-C
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57. UNEARTHED (OR IMPEDANCE-
EARTHED) NEUTRAL –IT
In IT system, the neutral from the transformer is isolated to
the earth and the metallic parts of equipment are connected
to the earth ground.
In case of electric fault, there is no danger, but if there are
two simultaneous faults, this will be a short circuit and
proper device should open the faulty circuit
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58. IT – 1ST FAULT
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59. IT – 2ND FAULT
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60. THE EARTHED
NEUTRAL –TT
The transformer neutral is earthed;
The frames of the electrical loads are also connected to an
earth connection.
The insulation fault current is limited by the impedance of the
earth connections and the faulty part is disconnected by a
Residual Current Device (RCD).
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61. THE EARTHED
NEUTRAL –TT
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62. THE EARTHED
NEUTRAL –TT
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63. THE EARTHED
NEUTRAL –TT
Ra – Installation ground earth impedance
Rb – Transformer (supply) ground earth impedance
Rc- Fault impedance
Uc – Contact voltage (50 V or 25 V)
Ud – Fault voltage
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𝐼𝑑 =
V
Ra + Rb + Rc
𝑈𝑑 = Ra ∗ Id

64. THE EARTHED
NEUTRAL –TT
The security device should open the circuit if Ud > Uc, in this
case the rating value of the RCD/ELCB is
I∆n≤ Uc/Ra
with I∆n as the sensibility of the RCD/ELCB
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65. THE EARTHED
NEUTRAL –TT
Protection against direct contact:
• The protection against direct contact is defined by the
IEC 60449-1. The RCD/ELCB has to have a sensibility
according to the threshold of sensation, 30 mA.
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66. RCD AND SENSITIVITY
Due to its design a RCD/ELCB does not guaranty to open the
circuit at the exact value of the sensibility. By standards, it
has been defined that a RCD/ELCB will trip for a
𝐼∆𝑛
2
≤ 𝐼𝐹 ≤ 𝐼∆𝑛
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67. ELCB VS RCD
RCD measure the phase and neutral current. If there is a
difference, that means there is an earth leakage. Earth
leakage can be detect even without earth pit connection. It is
working even if there is an earth connection fault.
ELCB measure the voltage between the earth and phase. It is
required a good earth connection. It does not work if there is
an earth connection fault.
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71. THANK YOU
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