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 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

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: 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: 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