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Electricity at Work
Basic Principles of Electricity
 Volt = Electrical pressure
 Ampere = Electric current flow
 Ohm = Electrical resistance (or impedance)
 Power (watts) = voltage x current
Electrical Hazards
 Electric shocks
 Electric burns
 Electrical fires
 Electric arcing
 Explosion
 Portable Electrical equipment
Electrical Control Measures
Insulation/Enclosure of live parts
 Low Voltages
 Earthing
 Fuse
 Circuit Breaker
 RCD
 Equipotential bonding
 Isolation

Insulation/Enclosure of Live Parts
 Live parts cannot be touched
 If equipment has a metal enclosure,
precautions must be taken to prevent
metalwork becoming live. This is achieved
by double insulation in which live parts are
covered by 2 layers of insulator.
 Each layer is capable of adequate
insulation
Low Voltages
 For hand tools, the 100 volt centre-tapped
(CTE) system is recommended.
 System relies on the mid-point of the
reduced voltage transformer to be earthed
 Maximum shock voltage is 55 volts, but full
110 volt supply powers the equipment
Earthing
 By connecting exposed metal parts to
earth, any fault current is provided with low
impedance path to earth I.e. one with little
resistance so that fault current will operate
protective devices and cut off the supply by
breaking the circuit
 If all exposed metalwork is properly
bonded to earth, it cannot be made live by a
fault and the risk of shock is eliminated.
Fuses
 Forms a weak link in a circuit by
overheating and melting by design if the
current exceeds the safe limit
 Rating should be above operating current
required by equipment but less than the
current rating of the cable in the circuit
Circuit Breakers
 A mechanical switch which automatically
opens if the circuit is overloaded
 Rating should be above operating current
required by equipment but less than the
current rating of the cable in the circuit
RCDs
 Interrupt supply in event of a small leak of
current to earth
 Sensitivity can be adjusted so that shocks
are not lethal
 Determine when a current flows to earth by
comparing current in live and neutral
conductors
 Test buttons should be regularly checked
Equipotential Bonding
 All extraneous metalwork is is connected
by a common bonding conductor which
ensures that all the metalwork is at the
same potential
 Current will not flow between two points at
the same potential
 A common connection to earth is usually
made
Isolation
 Isolation means depriving something of
power, AND ensuring that tit cannot be reenergised
 Establishes an effective barrier between
equipment and supply and ensures that no
unauthorised person is able to remove the
barrier
 Should be clearly labelled
Other Control Measures
 Insulating gloves
 Insulating mats
 FR clothing
 Insulated tools
 Face shields
 Shrouding
 Distance
Portable Electrical Equipment
Control Measures
 Regular checks/maintenance
 Roll out leads
 Do not use in harsh conditions
 Manufacturers instructions
 110v CTE system
Electricity at Work Regs 1989

Require that all electrical systems should be:
• Constructed & maintained to prevent danger
• Regularly checked & tested by a competent person
• Suitable & sufficient for the environment in which they are to be
used
• Protected by earthing, double earthing, double insulation and/or
RCDs
• Capable of being made dead (isolated)


Live working should only be used as a last resort and then
with all due precautions to prevent/minimise injury
Systems should normally be made dead, checked and
isolated so that they cannot accidentally become
energised – may require PtW systems
Maintaining Electrical Equipment
 User checks
 Formal visual inspections
 Combined Inspections and tests
 Maintenance and test records
 Frequency of maintenance
User Checks
 Check for:
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Damage to cable sheath
Damage to plug, casing or pins
Inadequate joints or taped joints
Coloured internal cables showing
Wet or contamination
Damage to external casing or loose parts or
screws
 Equipment should be taken out of use and
reported immediately
Formal Visual Inspections
 Carried out by competent person
 Most faults can be picked up this way
 Include removal of plug cover and checking
fuse
 Provide simple written guidance
 Faulty equipment should be taken out of
service and not used until properly repaired
 Data should be kept and can be used to
identify trends
Combined Inspection & Test
 Likely to be justified when:
• Reason to suspect equipment may be faulty
• After repair or modification
• At periods appropriate to the equipment
 PAT testing
Maintenance & Test Records
 Useful for reviewing & monitoring
effectiveness of maintenance regime
 Can be used as inventory of equipment and
a check on use of unauthorised equipment
 Can be used to identify trends
 Useful to label equipment
Frequency of Inspections
 Factors to consider:
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Type of equipment e.g. portable or hand held
Manufacturers recommendations
Initial integrity and soundness
Age of equipment
Working environment e.g. wet , hot, dusty
Frequency and duration of use
Foreseeable abuse of equipment
Effects of any modifications or repairs
Analysis of records of previous maintenance
Effects of Electric Shock
 Muscular contractions
 Respiratory failure
 Fibrillation of the heart
 Cardiac arrest
 Burns
 Can result in secondary injuries e.g. falls
from height or muscle tears
First Aid for Electric Shock
 Break contact between current and victim
either by switching off or removing victim
 Ensure rescuer does not come into contact
with anything live e.g. victims skin
 Artificial respiration should commence
immediately and continue until the victim
recovers or qualified medical aid
intervenes