IGC2 Elem 4 (Electrical Hazards and Controls)

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  • WEEK 2 ELEMENT 4Electrical Hazards and ControlPage: 98

  • Each year in the UK there are:30 workplace deaths30 domestic deathsElectric shock Electric burns Electrical arcing Fires ExplosionsElectricity: Introduction

  • Electrical Terms (1)Volt (Pressure difference):The unit of measurement of electrical pressureAmpere (Current):The unit of measurement of electric current flowOhm (Resistance):The unit of measurement of electrical resistance

    Page: 99

  • Electrical Terms (2)Direct Current (DC):The current flows in one direction between positive and negative terminalsAlternating Current (AC):The electric current is constantly reversing its direction of flow at a given frequencyFrequency:Measured in cycles per second is expressed in Hertz in UK 50 cycles per second

    Page: 100

  • Electrical Terms (3)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, woodPage: 100

  • Nature of ElectricityOhms 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/RIis measured in amps (A), which is the electron flow or currentVis measured in volts (V), potential difference or pressureRthe resistance is measured in ohms (), Page: 100

  • Ohms Law ExampleIf the applied voltage is 230V and circuit resistance is 1,000 ohms then the current flow will be 0.23A or 230 mA

    V / I = R 1,000 =0.23If we have two values then we are able to work out the third !230Page: 100

  • Electrical PowerAnother useful expression enables the electrical power (P), represented by the flow of electrical current in a circuit, to be determined.Power(P) = Voltage (V) x Current (I)When: Vis measured in volts (V) I is measured in amperes (A) W is given in watts (W)Page: 100

  • Main Dangers of ElectricityElectric Shock: Contact with live parts Direct Contact: Coming in to contact with a conductor that is supposed to be liveIndirect Contact: Coming into contact with a conductor that is not live in normal conditions but has become live due to a faultArcingFire & ExplosionBurns Page: 101

  • Severity of Electric ShockCurrent in amperesLength of contact time Path through the bodyConductivity/resistance of the bodyThe voltageConductivity of the environmentNature of the contactAge and health status of victim Page: 101

  • If a Person has received an Electric Shock

    Do not touch injured person until the current is switched off. If the current cannot be switched off, stand on some dry insulating material and use a wooden or plastic implement to remove the injured person from the electrical source.Administer first aid if qualifiedCall professional helpPage: 101

  • Main Dangers of ElectricityArcing: Electricity can jump an air gap causing shock effects to persons not in contact with conductorFire & Explosion: Flow of electricity generates heat. If large flow passes through unsuitable conductor heat can lead to fireBurns: Heat of arcing or excessive flow through body causes tissue damagePage: 102

  • Causes of Electrical FireInadequate circuits for the currentOverloaded circuitsIncorrect fuses (e.g. nails)Damaged wiring and insulationLoose connectionsOverheating of cablesOverheating due to thermal insulationOverheating due to lack of ventilationFlammable materials to close to electrical equipmentPage: 102

  • Effects on Body of ElectricityDamage to the nervous systemFibrillation (irregular heartbeat)Tissue burns at entry and exitDamage to internal organsMuscular contractionsPhysical traumaStopping breathing (respiratory paralysis)Stopping the heart (cardiac arrest)

    Page: 102

  • Secondary Effects of Electrical ShockFalls from heightUnintentional movement of machinery Failure of control measures & security systems Loss of information Corporate reputation Throw off sudden movement of the bodyPage: 102

  • Electricity Protection DevicesFusesCircuit breaker EarthingIsolationReduced voltage Battery operated toolsResidual Current Devices (RCD)Double insulationPage: 102

  • Fuse A specially designed weak link which is designed to melt at a predetermined value of currentPage: 103

    AdvantagesDisadvantagescheap and readily available protects equipmentwill not protect individuals slow to operateinaccurateunsuitable or wrong fuse may be usedeasy to overrideneeds tool to replace

  • Circuit BreakersElectromagnetic devices which perform the same function as fuses but operate fasterPage: 103

    AdvantagesDisadvantagesautomatically trip under fault conditionsno tools required to resetnot easy to defeatProtects equipment from overloadmay be mistaken for an RCDdo not protect the individual

  • Earthing (Earth Leakage Protectors)Earth lead and spikeElectricity will always try to reach earth and earthing is a means of providing a low resistance path to earth Page: 103

    AdvantagesDisadvantagesPrevent indirect electric shock

    Readily identifiedspecialist testing and maintenance, professional installationNo protection if removed

  • IsolationShutting off the electricity supply to an item of equipment and preventing the system from being mistakenly reconnected Page: 103

    AdvantagesDisadvantagessafest option as it eliminates electricitymay be physically locked offmay isolate other equipmentmay be reconnected without lock off prevents live fault finding

  • Reduced Voltage Systems (1)Page: 104

  • Reduced Voltage Systems (2)Reducing the mains voltage by means of a transformer to a lower safer voltage e.g. 110volts or 55 volts Page: 104

    AdvantagesDisadvantagesat 55V - injury is highly unlikelycolour coded cabling system for easy recognitionspecialist equipment e.g. Transformer required lead from supply to transformer at higher voltages, needing protection with RCD

  • Battery Operated ToolsPage: 104

    AdvantagesDisadvantageslittle risk during normal useNot restricted by cableNo trailing cablelimited use low power outputConstant charging required

  • Residual Current Devices (RCD) Compares the electricity flow to the equipment with the return flow and if a difference is detected the equipment is isolatedPage: 104

    AdvantagesDisadvantagesrapid and sensitivedifficult to defeateasy to use, test and resetcan not be reset with a fault on the circuitmay isolate crucial equipment if one RCD covers a number of distribution points e.g. freezers and computersmechanical device which could failNo overload protection

  • Double InsulationTwo separate layers of insulation are provided which allows for fault detection where one layer has failed the other still provides protection Page: 104

    AdvantagesDisadvantagestwo layers of insulation prevent user contact with any live parts no earth requiredphysical damage may defeat double insulationNo earth therefore no protection if used with equipment that requires earth

  • Portable Electrical EquipmentAccidents caused by:Using unsuitable apparatusInadequate maintenance or misuseUsing defective apparatusModifications by unauthorised personnelModifications whilst the appliance is liveUsing equipment in unsuitable environmentsNo system of inspection or removal of damaged equipmentPage: 105

  • Hazards of Portable Electrical EquipmentAreas to look at for hazardsPage: 105

    PlugCableJointsApplianceNo fuseRun overMakeshiftCasingDamage to plug casingDraggedLeads pulled out of cord gripWorn ConnectionsIncorrect wiringTrappedIncorrect wiringEarth wire detachedHeat/corrosive chemicalsPoor earth connectionsFlexingWrong connectionsInsulation

  • Precautions using Portable EquipmentReduced voltage operationUse of residual current circuit breakersProtected against overloadCables insulatedCorrect sheathingSufficient socket outletsUse of cable drumsCorrect maintenance and repairReduced voltage operationRegular inspections and checks Properly trained staffPage: 106

  • Types of InspectionUser checksFormal visual inspectionCombined inspection and test (PAT testing)Page: 107

  • Frequency of Inspection & TestManufacturers recommendations Age of equipmentRobustness of equipment Double insulated or earthed Type of cable (e.g. armoured)Extent of useUsers of equipment Environment Abuse or misuseHistory of equipmentPage: 108

  • Reason to keep records of inspection and testing of electrical equipment Inspection by authorised personb) In case test label removedc) Test frequencies maintainedd) Record actions of faults rectifiedPage: 109

  • Electrical Safety in Office EnvironmentsEquipment of approved standardMaintenance of fixed electrical installationsThere is a means of isolationConnections, wiring free from defectsCorrect fusesPlugs correctly wiredNo overloading of socketsAppliances switched off when not in usePAT testing in date Cables correctly routedRCDs usedSystem for reporting of defectsPage: 109

  • Precautions for on Working Live EquipmentTrained and Competent StaffAccompanied by another personAdequate Information about the risksSuitable insulated toolsInsulated barriers or screensSuitable instruments and test probesPersonal protective equipment/rubber matsPermit to workRestricted accessPage: 109

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