Electricity at Work

1
Electricity at Work
2
Basic Principles of Electricity

• Volt Electrical pressure
• Ampere Electric current flow
• Ohm Electrical resistance (or impedance)
• Power (watts) voltage x current

3
Electrical Hazards

• Electric shocks
• Electric burns
• Electrical fires
• Electric arcing
• Explosion
• Portable Electrical equipment

4
Electrical Control Measures

• Insulation/Enclosure of live parts
• Low Voltages
• Earthing
• Fuse
• Circuit Breaker
• RCD
• Equipotential bonding
• Isolation

5
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

6
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

7
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.

8
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

9
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

10
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

11
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

12
Isolation

• Isolation means depriving something of power, AND
  ensuring that tit cannot be re-energised
• Establishes an effective barrier between
  equipment and supply and ensures that no
  unauthorised person is able to remove the barrier
• Should be clearly labelled

13
Other Control Measures

• Insulating gloves
• Insulating mats
• FR clothing
• Insulated tools
• Face shields
• Shrouding
• Distance

14
Portable Electrical Equipment Control Measures

• Regular checks/maintenance
• Roll out leads
• Do not use in harsh conditions
• Manufacturers instructions
• 110v CTE system

15
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

16
Maintaining Electrical Equipment

• User checks
• Formal visual inspections
• Combined Inspections and tests
• Maintenance and test records
• Frequency of maintenance

17
User Checks

• Check for
• 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

18
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

19
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

20
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

21
Frequency of Inspections

• Factors to consider
• 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

22
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

23
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