The document provides a comprehensive overview of miniature circuit breakers (MCBs) and fuses, detailing their definitions, working principles, types, and applications. MCBs are electromechanical devices that interrupt current flow during overloads and short circuits, whereas fuses are safety devices that protect equipment from excessive current by melting a metal wire. The document also discusses the advantages and disadvantages of both devices, earthing systems, types of earthing, electrical components, and the roles of electricians.

1. MCB and Fuse
Understanding the meaning of MCB
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2. Meaning of MCB.
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 MCB stands for Miniature Circuit Breaker. It is an electromechanical device
that works based on the electromagnetic as well as the thermal properties
of the electric current. An electromagnetic mechanism present inside the
MCB helps it to instantaneously interrupt the current flow during short
circuits and the bimetallic strip present in it helps it to interrupt the current
flow during overloads.

3. Working Principle of MCB
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 Working Principle of MCB
When the current overflow occurs through MCB – Miniature Circuit
Breaker, the bimetallic strip gets heated and deflects by bending. The
deflection of the bi-metallic strip releases a latch. The latch causes the MCB to
turn off by stopping the current flow in the circuit.

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6. Types of MCBDifferent Types of MCB Based
on their Trip Curves
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These are some features of the MCB:
•Its current rating is a hundred amperes.
•It operates thermally.
•Usually, its tripping is not controllable.
MCB can be easily operated and thus offers improved
operational safety and greater convenience without
incurring an expensive operating cost.
They find use to protect lower current circuits and have the
following specifications:
•Current rating – Amperes
•Short Circuit Rating – Kilo Amperes (kA)
•Operating Characteristics – B, C, D, Z or K Curves

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8. Continued…..
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•Type B MCB
•Type C MCB
•Type D MCB
•Type K MCB
•Type Z MCB
Type B MCB
B types trip if the current flowing through hits between three and five times
the recommended maximum.
Type B is the most sensitive types of MCB, designed for domestic and low
voltage commercial settings where any current surges are likely to be
small like lighting circuits, home wirings, etc.
•Functions of Type B MCB are protection for people and big-length
cables in TN and IT systems.

9. Type C MCB
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Type C MCB
C types trip at currents between five and ten times their rated load. They find
use in commercial or industrial types of applications where there could be
chances of higher values of short circuit currents in the circuit.
Good examples include smaller electric motors, fans, fluorescent lighting,
small transformers, pilot devices, control circuits, coils, etc.
•Functions of Type C MCB are protection for resistive and inductive loads
with low inrush current

10. Type D
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Type D MCB
D type MCBs are the least sensitive type, only activating when current surges to
between ten and twenty times the recommended maximum.
Examples include welding equipment, X-ray machines, UPS systems, large
motors, uninterruptible power supply units, industrial welding equipment, etc.
•Functions of Type D MCB are protection for circuits that supply loads with high
inrush current at the circuit closing (transformers, breakdown lamps).

11. Tripping Current and Operating Current of
MCB’s
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Type Tripping Current Operating Time
Type B 3 To 5 times the full load current 0.04 To 13 Sec
Type C
5 To 10 times the full load
current
0.04 To 5 Sec
Type D
10 To 20 times the full load
current
0.04 To 3 Sec
Type K
8 To 12 times the full load
current
<0.1 Sec
Type Z 2 To 3 times the full load current <0.1 Sec

12. Types of MCBs based on the number
of poles
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•Single Pole MCB
•Double pole MCB
•Triple Pole MCB
•Three poles with a neutral
•Four Poles

13. Explanation
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Single Pole MCB
A single-pole circuit breaker has one switch and also protects a single phase of
the circuit.
Double pole MCB
The double pole circuit breaker has two switches and also protects two-phase and
neutral.
Triple Pole MCB
A three-pole circuit breaker has three switches, and they also protect the three
phases.
Three poles with a neutral
Three poles and a neutral circuit breaker protect the three phases of the circuit. It
also has a neutral switch.
Four Poles
A four-pole MCB contains four switches, three phases, and a neutral. But unlike the
three poles with neutral, the four poles protect all the phases and the neutral. They
are used in places with an unbalanced circuit.

14. Types of MCB amps Ratings
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The following lists some of the most frequently encountered load capacities for
commercial MCBs:
•6 amps
•10 amps
•16 amps
•20 amps
•25 amps
•32 amps
Applications of MCB’s
•Home Electrical Panels
•Heaters
•Lights
•Industrial Applications( industries requires up to 30 kA of power supply)

15. Are There Any Disadvantages to MCB?
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 MCBs are more expensive than fuses.
 MCB distribution board is more costly than a rewireable fuse board
 The probability of overloading the circuit is eliminated by operating by
someone who is unqualified.
Advantages Of MCB’s
 MCBs allow quick restoration of power supply.
 MCBs are safer than a fuse.
 MCBs offer better protection against electrical faults
 MCBs are much more sensitive to faults than fuses
 They act faster than fuse during short circuits
 Offer better overload protection than fuses.
 Offers a safer interruption of short-circuit current and arc quenching.
 Handling MCB is electrically much safer than a fuse.

16. Practical Based On MCB
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17. Overload Circuit
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18. Fuses
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19. Transistor Checking
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20. Images For Fuses
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21. Working Principle of an Electrical Fuse
• Current flows in a loop
• Heating effect of current
Electric current can flow through a conductor only when the circuit formed is
complete. If there is a break in the loop, electric charges cannot flow through.
This is also how switches operate.
For example, when you put on the light switches at home, the lights come on
because you have just completed the circuit allowing charges from the power
source to flow through and power your lights.
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22. Types of Fuses
• Different types of fuses are available in the market, and they are classified on
the basis of different aspects. But mainly, fuses can be divided into two
categories based on the input supply as follows:
• AC fuses
• DC fuses
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24. Principle of Electrical Fuse
• The primary use of an electric fuse is to protect electrical equipment from
excessive current and to prevent short circuits or mismatched loads.
• Electrical fuses play the role of miniature circuit breakers.
• Apart from protecting equipment, they are also used as safety measures to
prevent any safety hazards to humans.
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25. Electrical Fuse - The Working Principle
• Introduction
• An electrical fuse is a safety device that operates to provide protection against the
overflow of current in an electrical circuit.
• An important component of an electrical fuse is a metal wire or strip that melts
when excess current flows through it.
• It helps to protect the device by stopping or interrupting the current.
• In this article, let us know in detail about the Working Principle of the electrical fuse
and its functions and types.
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26. Function of Fuse
• Acts as a barrier between the electric circuit and the human body
• Prevents device failure due to faulty circuit operation
• Fuse prevents short-circuits
• Prevents overload and blackouts
• Prevents damage that is caused due to mismatched loads
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27. Experiment
• Describe an experiment to illustrate the action of an electric fuse.
• Take a thin fuse wire made of tin or tin-alloy having low melting point. Place
this fuse wire on the porcelain fuse grip and insert the grip into the fuse
holder. Now switch on all the electrical appliances of high power rating like
electric iron, water heater, air conditioner, etc., . Since the melting point of
the fuse wire is much lower, it melts and breaks the circuit.
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28. Give the circuit symbol for a fuse.
Explain its importance in a circuit.
A fuse is a very important device used for protecting electric circuits. It is a wire made out of
a metal like tin or tin alloy having a very low melting point. When a high current flows
through a circuit, the fuse wire gets heated or melts due to short circuiting or overloading.
Hence the circuit is broken and the current stops flowing. This saves all the appliances of the
circuit. Fuse wires are of various capacities. A fuse with 5 ampere capacity will be thinner
than a fuse with 15 ampere capacity. A fuse of 5 amps is used in circuits where lights and
fans are connected whereas a fuse of 15 amps is used in power circuits where appliances like
electric heater, geyser, electric iron and air conditioner are connected.
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29. Selection of swithces
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• SPST = Single Pole, Single Throw
• SPDT = Single Pole, Double Throw
• DPST = Double Pole, Single Throw
• DPDT = Double Pole, Double Throw

30. Continued.....
• Pole - number of switch contact sets.
• Throw - number of conducting positions (only used for single and double)
• Way - number of conducting positions.
• Momentary - switch returns to its normal position when released.
• Open - off position, contacts not conducting.
• Closed - on position, contacts conducting, there may be several on positions.
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31. SPST-Switch
• ON-OFF, SPST
• SPST = Single Pole, Single Throw
• SPST on-off switch symbolSPST toggle switch, photograph © Rapid Electronics
• A simple on-off switch.
• This type can be used to switch the power supply to a circuit. The photograph
shows a SPST toggle switch
• When used with mains electricity this type of switch must be in the live wire, but it
is better to use a DPST switch to isolate both live and neutral.
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32. Earthing
• Earthing is used to protect you from an electric shock. It does this by
providing a path (a protective conductor) for a fault current to flow to earth.
It also causes the protective device (either a circuit-breaker or fuse) to switch
off the electric current to the circuit that has the fault.
• An earthing system or grounding system connects specific parts of an
electric power system with the ground, typically the Earth's conductive
surface, for safety and functional purposes
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33. Earthing Rules
• According to IEE regulations and IE rules, earth pin in 3 pin plus sockets
and 4 pin power sockets must be efficiently and permanently earthed.
• All metal casings and metal coverings containing or covering electrical supply
cable or equipment must be earthed. The metallic frames of generators,
transformers, stationary motors etc.
• Stay wires for the overhead electric lines must be connected to earth at
atleast one strand to the earth wires.
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34. Without Earting....Causes
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35. Fault current......
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36. Earthing Construction...
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37. Types of earthing
• Types of Earthing
• There are three types of earthing,
they are:
• Pipe earthing
• Plate earthing
• Strip earthing
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38. Plate Earthing and Strip Earthing
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39. Rod earthing Images...
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40. Earthing Rules
• According to IEE regulations and IE rules, earth pin in 3 pin plus
sockets and 4 pin power sockets must be efficiently and permanently
earthed. All metal casings and metal coverings containing or covering
electrical supply cable or equipment must be earthed. The metallic
frames of generators, transformers, stationary motors etc.
• Stay wires for the overhead electric lines must be connected to earth at
atleast one strand to the earth wires.
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41. Components of Electrical Earthing System
• Earth Continuity Conductor
• Earthing Lead
• Earth Electrode
• Earth Continuity Conductor or
Earth Wire
The conductor that connects all
metallic part of the electrical
installation like the conduit, metallic
shells, ducts, plug sockets, distribution
boxes, fuses, controlling and
regulating devices, metallic parts of
transformers, motors, generators etc.
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42. Earth Continuity Conductor(Cable)
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The conductor that connects all metallic part of the electrical installation like the conduit, metallic shells, ducts, plug sockets, distributi
fuses, controlling and regulating devices, metallic parts of transformers, motors, generators etc.

43. Earth Continuity Conductor (bare copper
conductor
• Earth Continuity Conductor
(bare copper conductor.
• The earth continuity conductor’s
resistance must be very low. As
per IEEE rules, the resistance
between the consumer earth
terminal and the earth
continuity conductor must be
less and 1 ohms.
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44. Earthing Lead or Earthing Joint
• he conductor connecting the earth
continuity conductor and the earth
electrode is called earthing lead or
earthing joint. The point where the
earthing lead meets the earth
continuity conductor meet is called
connecting point.
• Copper strip used as Earthign Lead
If there are 2 earth electrode there
should be 4 earthing leads. This isn’t
for providing parallel path for fault
current but for carrying fault current
simultaneously giving added safety.
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45. Copper strip used as Earthign Lead
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46. Important Terms
• Earth: The connection of an electrical
installation through a conductor to
another conductor buried in earth.
• Solidly Earthed: An electrical
installation or appliance is said to be
solidly earthed when it is connected to
earth conductor/wire directly without
using a circuit breaker, fuse, impedance
or any other safety devices or elements
• Earth Electrode: A conductor
buried in earth for the purpose of
electrical earthing is known as earth
electrode. The shape of the earth
electrode may vary from conductive
rod, conductive plate, metal water
pipe or any other conductor with
low resistance. Earth electrodes are
made of copper, galvanised iron,
cast iron etc.
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47. Continued....
• Earth Lead: The conductive strip or
wire that connects an electrical
installation or appliance to the earth
electrode is called Earth Lead. Earth
lead can be of copper, galvanized iron
etc.
• Sub Main Earthing Conductor: the
wire connecting the distribution board
to various switch boards. Flexible wires
are used as sub main earthing
conductor.
• Earth Continuity Conductors: They are the
conductors used for connecting the earth lead to
various electrical appliances and devices such as
distribution boards, electrical sockets, appliances
etc. It may be in the form of flexible wire, cable
metallic covering or metallic pipe.
• Earth Resistance: The resistance between the
earth and earth electrode is called earth resistance.
It is the resistance of earth electrode, earth lead,
earth continuity conductor and earth added up
algebraically. The earth resistance is measured
using Earth Megger.
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48. Advantages of Earthing
• Earthing is the safe and the best
method of offering safety. We know
that the earth’s potential is zero and is
treated as Neutral. Since low
equipment is connected to earth using
low resistance wire, balancing is
achieved.
• Metal can be used in electrical
installations without looking for its
conductivity, proper earthing ensures
that metal does not transfer current.
• A sudden surge in voltage or
overload does not harm the device
and person if proper earthing
measures are done.
• It prevents the risk of fire hazards
that could otherwise be caused by
the current leakage.
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49. Definition of Earthing...
• Earthing is defined as “the
process in which the
instantaneous discharge of the
electrical energy takes place by
transferring charges directly to
the earth through low resistance
wire.”
• To ensure safety, earthing can be done by
connecting the electrical appliance to
earthing systems or electrodes placed
near the soil or below the ground level.
• The electrode or earthing mat equipped
with a flat iron riser is installed under the
ground level. It helps to connect all the
non-current-carrying metallic parts of
the equipment
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50. Resistors sries and Parallel Connection
• you can calculate the voltage across
the three resistors at a time and the
formula is.
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51. Series Connection
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• Two or more resistors are said to be
connected in series when the same
amount of current flows through all
the resistors. In such circuits, the
voltage across each resistor is different.
In a series connection, if any resistor is
broken or a fault occurs, then the
entire circuit is turned off. The
construction of a series circuit is
simpler compared to a parallel circuit.

52. Continued....
• The figure above shows the ‘n’
number of resistors connected in
parallel. The following relation
gives the total resistance here
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Circuit Components

53. Ohm's law
• Ohm's law states that the voltage
across a conductor is directly
proportional to the current flowing
through it, provided all physical
conditions and temperatures
remain constant.
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54. Problems Based On Ohm’s Law
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55. Roles and Responsibilities of an electrician
• Installs and repairs electrical wiring, systems, and fixtures in buildings.
• Installs conduits and pipes to house electrical wires and cables.
• Ensures piping complies with electrical codes.
• Installs circuit breakers and other electrical hardware and connects wiring
to them.
• Connects electrical systems to powerlines to provide electricity to the
building.
• Tests electrical systems to ensure proper installation and operation.
• Inspects electrical systems to determine whether repairs are needed.
• Replaces conduit and wiring as needed.
• Required Skills/Abilities:
• Ability to read blueprints.
• Extensive knowledge of electrical systems and
wiring.
• Ability to use hand tools and power tools.
• Proficient in the use of test meters and other
diagnostic equipment.
• Excellent analytical and problem-solving skills.
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56. What is Electrical Safety?
• Electrical safety is a general practice of
workers who are exposed to handling
and maintaining electrically powered
equipment. It is a set of guidelines
they follow to mitigate electrical
hazards and prevent its dangerous
effects in case of an incident. Unable
to adhere to electrical safety can lead
to accidents, near misses, or even
fatalities.
• Importance
• Working around electricity can be
very safe on the job site when
workers properly identify and
control hazards. But, inadequate
training, lack of experience, and
failure to recognize potential
hazards could result in electric
shock or death.
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57. Electrical Hazards Examples & Tips for Safety
• Overhead Power Lines
• Overhead powered and energized
electrical lines have high voltages
which can cause major burns and
electrocution to workers.
Remember to maintain a minimum
distance of 10 feet from overhead
power lines and nearby equipment.
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58. Continued...
• Damaged Tools and Equipment
• Exposure to damaged electrical
tools and equipment can be very
dangerous. Do not fix anything
unless you are qualified to do so.
• Inadequate Wiring and Overloaded
Circuits
• Using wires of inappropriate size
for the current can cause
overheating and fires to occur. Use
the correct wire suitable for the
operation and the electrical load to
work on. Use the correct extension
cord designed for heavy-duty use.
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59. Continued....
• Exposed Electrical Parts
• Examples of exposed electrical
parts include temporary lighting,
open power distribution units, and
detached insulation parts on
electrical cords.
• Improper Grounding
• The most common OSHA
electrical violation is the improper
grounding of equipment. Proper
grounding can eliminate unwanted
voltage and reduce the risk of
electrocution.
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60. Continued....
• Damaged Insulation
• Defective or inadequate insulation
is a hazard. Be aware of damaged
insulation and report it
immediately.
• Wet Conditions
• Never operate electrical equipment
in wet locations. Water greatly
increases the risk of electrocution
especially if the equipment has
damaged insulation.
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61. Safety signs....
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62. Electrical Tools and Equipments
• Adjustable strippers
• these combine stripping with
crimping and wire-snipping
abilities.
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63. Insulated screwdrivers
• Screwdrivers are one of the most
traditional of tools but are still
indispensable for most electricians
who frequently require access to
electrical containers sealed with
screws. There are multiple sizes and
shapes available for compatibility
with the abundance of screw
designs.
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64. Types of pliers
• Long nose pliers-
• Combination pliers–
• Water pump pliers–
• Side-cutting pliers–
• Mole grips/ locking pliers–
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65. Electrical tape
• Electrical tape is used to insulate
wires or other items that conduct
electricity. Also known as insulation
tape or electrical insulation tape, it
is self-adhesive and pressure-
sensitive, built to resist abrasion,
heat and liquids in order to protect
the sensitive conducting core within
electrical wiring.
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66. Hacksaws
• Hacksaws are fine-toothed saws
designed primarily for cutting
through metal. The thin blades are
held at tension in an adjustable
frame, between the head of the saw
and the pistol grip handle. These
blades can break or become blunt
but are easily replaceable.
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67. Cable cutters
• Cable cutters are a staple of every
electrician’s tool kit. These versatile
tools feature steel blades and cut
through standard wiring easily.
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68. Spanners
• Spanners will almost certainly be an
essential inclusion in your tool kit if
you regularly need to loosen or
attach nuts, bolts or similar fixings.
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69. Voltage tester
• Voltage indicators, or
‘multimeters’, are handheld devices
used for – you guessed it – testing
whether a live current is present in
a particular location.
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70. Safety knife
• Safety knives are not just a
specialist professional tool – they
are in fact familiar to most of us.
We may know them as Stanley
knives, utility knives, pen knives or
box cutters.
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71. Hex keys
• Hex keys take their name from the
hexagonal fasteners and fixings
they are used to adjust. Another
common name is Allen key or
Allen wrench
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72. Claw Hammer
• Claw hammers feature a standard
hammer on one side of the tool,
primarily used for inserting fixtures
like nails, and a dual steel claw at
the other end, which is designed to
enable the easy removal of the
same nails or similar fixtures by
applying a robust grip.
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73. Tools Complete
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74. Continued....
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