IGC2 Elem 4 Electrical Hazards and Controls
IGC2 Elem 4 Electrical Hazards and Controls
IGC2 Elem 4 Electrical Hazards and Controls
NEBOSH
WEEK 2 – ELEMENT 4
Electrical Hazards
and Control
NEBOSH
Electricity: Introduction
Each year in the UK there are:
30 workplace deaths
30 domestic deaths
• Electric shock
• Electric burns
• Electrical arcing
• Fires
• Explosions
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Ampere (Current):
The unit of measurement of electric current flow
Ohm (Resistance):
The unit of measurement of electrical resistance
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Frequency:
Measured in cycles per second is expressed in Hertz
in UK 50 cycles per second
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Conductors:
A material that allows electricity to flow easily :- e.g.
copper, steel, water
Insulators:
Materials that have a high resistance to electrical
current:- e.g. plastic, rubber, wood
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Nature of Electricity
Ohms Law
The higher the electrical pressure (V) or the lower the
circuit resistance (R), the higher is the current that flows
in an electrical circuit:
I = V/R
I is measured in amps (A), which is the electron flow
or current
V is measured in volts (V), potential difference or
pressure
R the resistance is measured in ohms (Ω),
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Electrical Power
Another useful expression enables the electrical power
(P), represented by the flow of electrical current in a
circuit, to be determined.
2) Arcing
3) Fire & Explosion
4) Burns
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Fuse
A specially designed weak link which is designed to
melt at a predetermined value of current
Advantages Disadvantages
• cheap and readily • will not protect
available individuals
• protects equipment • slow to operate
• inaccurate
• unsuitable or wrong fuse
may be used
• easy to override
• needs tool to replace
Page: 103
NEBOSH
Circuit Breakers
Electromagnetic devices which perform the
same function as fuses but operate faster
Advantages Disadvantages
• automatically trip under • may be mistaken for an
fault conditions RCD
• no tools required to reset • do not protect the
• not easy to defeat individual
• Protects equipment from
overload
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Advantages Disadvantages
• Prevent indirect electric • specialist testing and
shock maintenance, professional
installation
• Readily identified • No protection if removed
Isolation
Shutting off the electricity supply to an item of
equipment and preventing the system from being
mistakenly reconnected
Advantages Disadvantages
• safest option as it • may isolate other
eliminates electricity equipment
• may be physically locked • may be reconnected
off without lock off
• prevents live fault finding
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Advantages Disadvantages
• at 55V - injury is highly • specialist equipment e.g.
unlikely Transformer required
• colour coded cabling • lead from supply to
system for easy transformer at higher
recognition voltages, needing
protection with RCD
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Advantages Disadvantages
• little risk during normal • limited use
use • low power output
• Not restricted by cable • Constant charging
• No trailing cable required
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NEBOSH
Residual Current Devices
(RCD)
Compares the electricity flow to the equipment with the return
flow and if a difference is detected the equipment is isolated
Advantages Disadvantages
• rapid and sensitive • may isolate crucial
• difficult to defeat equipment if one RCD
• easy to use, test and reset covers a number of
distribution points e.g.
• can not be reset with a freezers and computers
fault on the circuit
• mechanical device which
could fail
• No overload protection
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NEBOSH
Double Insulation
Two separate layers of insulation are provided which
allows for fault detection where one layer has failed
the other still provides protection
Advantages Disadvantages
• two layers of insulation • physical damage may
prevent user contact with defeat double insulation
any live parts • No earth therefore no
• no earth required protection if used with
equipment that requires
earth
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Types of Inspection
1) User checks
2) Formal visual inspection
3) Combined inspection and
test (PAT testing)
Page: 108
NEBOSH