Electricity at Work

Basic Principles of ElectricityVolt = Electrical pressureAmpere = Electric current flowOhm = Electrical resistance (or impedance)Power (watts) = voltage x current

Electrical HazardsElectric shocksElectric burnsElectrical firesElectric arcingExplosionPortable Electrical equipment

Electrical Control MeasuresInsulation/Enclosure of live partsLow VoltagesEarthing FuseCircuit BreakerRCDEquipotential bondingIsolation

Insulation/Enclosure of Live PartsLive parts cannot be touchedIf 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 VoltagesFor hand tools, the 100 volt centre-tapped (CTE) system is recommended.System relies on the mid-point of the reduced voltage transformer to be earthedMaximum shock voltage is 55 volts, but full 110 volt supply powers the equipment

EarthingBy 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 circuitIf all exposed metalwork is properly bonded to earth, it cannot be made live by a fault and the risk of shock is eliminated.

FusesForms a weak link in a circuit by overheating and melting by design if the current exceeds the safe limitRating should be above operating current required by equipment but less than the current rating of the cable in the circuit

Circuit BreakersA mechanical switch which automatically opens if the circuit is overloadedRating should be above operating current required by equipment but less than the current rating of the cable in the circuit

RCDsInterrupt supply in event of a small leak of current to earthSensitivity can be adjusted so that shocks are not lethalDetermine when a current flows to earth by comparing current in live and neutral conductorsTest buttons should be regularly checked

Equipotential BondingAll extraneous metalwork is is connected by a common bonding conductor which ensures that all the metalwork is at the same potentialCurrent will not flow between two points at the same potentialA common connection to earth is usually made

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

Other Control MeasuresInsulating glovesInsulating matsFR clothingInsulated toolsFace shieldsShroudingDistance

Portable Electrical Equipment Control MeasuresRegular checks/maintenanceRoll out leadsDo not use in harsh conditionsManufacturers instructions110v CTE system

Electricity at Work Regs 1989Require that all electrical systems should be:Constructed & maintained to prevent dangerRegularly checked & tested by a competent personSuitable & sufficient for the environment in which they are to be usedProtected by earthing, double earthing, double insulation and/or RCDsCapable of being made dead (isolated)Live working should only be used as a last resort and then with all due precautions to prevent/minimise injurySystems should normally be made dead, checked and isolated so that they cannot accidentally become energised may require PtW systems

Maintaining Electrical EquipmentUser checksFormal visual inspectionsCombined Inspections and testsMaintenance and test recordsFrequency of maintenance

User ChecksCheck for:Damage to cable sheathDamage to plug, casing or pinsInadequate joints or taped jointsColoured internal cables showingWet or contaminationDamage to external casing or loose parts or screwsEquipment should be taken out of use and reported immediately

Formal Visual InspectionsCarried out by competent personMost faults can be picked up this wayInclude removal of plug cover and checking fuseProvide simple written guidanceFaulty equipment should be taken out of service and not used until properly repairedData should be kept and can be used to identify trends

Combined Inspection & TestLikely to be justified when:Reason to suspect equipment may be faultyAfter repair or modificationAt periods appropriate to the equipmentPAT testing

Maintenance & Test RecordsUseful for reviewing & monitoring effectiveness of maintenance regimeCan be used as inventory of equipment and a check on use of unauthorised equipmentCan be used to identify trendsUseful to label equipment

Frequency of InspectionsFactors to consider:Type of equipment e.g. portable or hand heldManufacturers recommendationsInitial integrity and soundnessAge of equipmentWorking environment e.g. wet , hot, dustyFrequency and duration of useForeseeable abuse of equipmentEffects of any modifications or repairsAnalysis of records of previous maintenance

Effects of Electric ShockMuscular contractionsRespiratory failureFibrillation of the heartCardiac arrestBurnsCan result in secondary injuries e.g. falls from height or muscle tears

First Aid for Electric ShockBreak contact between current and victim either by switching off or removing victimEnsure rescuer does not come into contact with anything live e.g. victims skinArtificial respiration should commence immediately and continue until the victim recovers or qualified medical aid intervenes