Electricity at WorkElectricity at Work

Basic Principles of Basic Principles of ElectricityElectricity

Volt = Electrical pressureVolt = Electrical pressure Ampere = Electric current flowAmpere = Electric current flow Ohm = Electrical resistance (or Ohm = Electrical resistance (or

impedance)impedance) Power (watts) = voltage x currentPower (watts) = voltage x current

Electrical HazardsElectrical Hazards

Electric shocksElectric shocks Electric burnsElectric burns Electrical firesElectrical fires Electric arcingElectric arcing ExplosionExplosion Portable Electrical equipmentPortable Electrical equipment

Electrical Control Electrical Control MeasuresMeasures

Insulation/Enclosure of live partsInsulation/Enclosure of live parts Low VoltagesLow Voltages Earthing Earthing FuseFuse Circuit BreakerCircuit Breaker RCDRCD Equipotential bondingEquipotential bonding IsolationIsolation

Insulation/Enclosure of Live Insulation/Enclosure of Live PartsParts

Live parts cannot be touchedLive parts cannot be touched If equipment has a metal enclosure, If equipment has a metal enclosure,

precautions must be taken to precautions must be taken to prevent metalwork becoming live. prevent metalwork becoming live. This is achieved by double This is achieved by double insulation in which live parts are insulation in which live parts are covered by 2 layers of insulator.covered by 2 layers of insulator.

Each layer is capable of adequate Each layer is capable of adequate insulationinsulation

Low VoltagesLow Voltages

For hand tools, the 100 volt centre-For hand tools, the 100 volt centre-tapped (CTE) system is recommended.tapped (CTE) system is recommended.

System relies on the mid-point of the System relies on the mid-point of the reduced voltage transformer to be reduced voltage transformer to be earthedearthed

Maximum shock voltage is 55 volts, Maximum shock voltage is 55 volts, but full 110 volt supply powers the but full 110 volt supply powers the equipmentequipment

EarthingEarthing

By connecting exposed metal parts to By connecting exposed metal parts to earth, any fault current is provided with earth, any fault current is provided with low impedance path to earth I.e. one low impedance path to earth I.e. one with little resistance so that fault with little resistance so that fault current will operate protective devices current will operate protective devices and cut off the supply by breaking the and cut off the supply by breaking the circuitcircuit

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

FusesFuses

Forms a weak link in a circuit by Forms a weak link in a circuit by overheating and melting by design overheating and melting by design if the current exceeds the safe if the current exceeds the safe limitlimit

Rating should be above operating Rating should be above operating current required by equipment but current required by equipment but less than the current rating of the less than the current rating of the cable in the circuitcable in the circuit

Circuit BreakersCircuit Breakers

A mechanical switch which A mechanical switch which automatically opens if the circuit is automatically opens if the circuit is overloadedoverloaded

Rating should be above operating Rating should be above operating current required by equipment but current required by equipment but less than the current rating of the less than the current rating of the cable in the circuitcable in the circuit

RCDsRCDs

Interrupt supply in event of a small Interrupt supply in event of a small leak of current to earthleak of current to earth

Sensitivity can be adjusted so that Sensitivity can be adjusted so that shocks are not lethalshocks are not lethal

Determine when a current flows to Determine when a current flows to earth by comparing current in live earth by comparing current in live and neutral conductorsand neutral conductors

Test buttons should be regularly Test buttons should be regularly checkedchecked

Equipotential BondingEquipotential Bonding

All extraneous metalwork is is All extraneous metalwork is is connected by a common bonding connected by a common bonding conductor which ensures that all conductor which ensures that all the metalwork is at the same the metalwork is at the same potentialpotential

Current will not flow between two Current will not flow between two points at the same potentialpoints at the same potential

A common connection to earth is A common connection to earth is usually madeusually made

IsolationIsolation

Isolation means depriving Isolation means depriving something of power, something of power, ANDAND ensuring ensuring that tit cannot be re-energisedthat tit cannot be re-energised

Establishes an effective barrier Establishes an effective barrier between equipment and supply between equipment and supply and ensures that no unauthorised and ensures that no unauthorised person is able to remove the person is able to remove the barrierbarrier

Should be clearly labelledShould be clearly labelled

Other Control MeasuresOther Control Measures

Insulating glovesInsulating gloves Insulating matsInsulating mats FR clothingFR clothing Insulated toolsInsulated tools Face shieldsFace shields ShroudingShrouding DistanceDistance

Portable Electrical Portable Electrical Equipment Control Equipment Control MeasuresMeasures

Regular checks/maintenanceRegular checks/maintenance Roll out leadsRoll out leads Do not use in harsh conditionsDo not use in harsh conditions Manufacturers instructionsManufacturers instructions 110v CTE system110v CTE system

Electricity at Work Regs Electricity at Work Regs 19891989

Require that all electrical systems should be:Require that all electrical systems should be:• Constructed & maintained to prevent dangerConstructed & maintained to prevent danger• Regularly checked & tested by a competent personRegularly checked & tested by a competent person• Suitable & sufficient for the environment in which they are Suitable & sufficient for the environment in which they are

to be usedto be used• Protected by earthing, double earthing, double insulation Protected by earthing, double earthing, double insulation

and/or RCDsand/or RCDs• Capable of being made dead (isolated)Capable of being made dead (isolated)

Live working should only be used as a last resort Live working should only be used as a last resort and then with all due precautions to and then with all due precautions to prevent/minimise injuryprevent/minimise injury

Systems should normally be made dead, checked Systems should normally be made dead, checked and isolated so that they cannot accidentally and isolated so that they cannot accidentally become energised – may require PtW systemsbecome energised – may require PtW systems

Maintaining Electrical Maintaining Electrical EquipmentEquipment

User checksUser checks Formal visual inspectionsFormal visual inspections Combined Inspections and testsCombined Inspections and tests Maintenance and test recordsMaintenance and test records Frequency of maintenanceFrequency of maintenance

User ChecksUser Checks

Check for:Check for:• Damage to cable sheathDamage to cable sheath• Damage to plug, casing or pinsDamage to plug, casing or pins• Inadequate joints or taped jointsInadequate joints or taped joints• Coloured internal cables showingColoured internal cables showing• Wet or contaminationWet or contamination• Damage to external casing or loose Damage to external casing or loose

parts or screwsparts or screws Equipment should be taken out of Equipment should be taken out of

use and reported immediatelyuse and reported immediately

Formal Visual InspectionsFormal Visual Inspections

Carried out by competent personCarried out by competent person Most faults can be picked up this wayMost faults can be picked up this way Include removal of plug cover and Include removal of plug cover and

checking fusechecking fuse Provide simple written guidanceProvide simple written guidance Faulty equipment should be taken Faulty equipment should be taken

out of service and not used until out of service and not used until properly repairedproperly repaired

Data should be kept and can be used Data should be kept and can be used to identify trendsto identify trends

Combined Inspection & Combined Inspection & TestTest

Likely to be justified when:Likely to be justified when:• Reason to suspect equipment may be Reason to suspect equipment may be

faultyfaulty• After repair or modificationAfter repair or modification• At periods appropriate to the At periods appropriate to the

equipmentequipment PAT testingPAT testing

Maintenance & Test Maintenance & Test RecordsRecords

Useful for reviewing & monitoring Useful for reviewing & monitoring effectiveness of maintenance effectiveness of maintenance regimeregime

Can be used as inventory of Can be used as inventory of equipment and a check on use of equipment and a check on use of unauthorised equipmentunauthorised equipment

Can be used to identify trendsCan be used to identify trends Useful to label equipmentUseful to label equipment

Frequency of InspectionsFrequency of Inspections

Factors to consider:Factors to consider:• Type of equipment e.g. portable or hand Type of equipment e.g. portable or hand

heldheld• Manufacturers recommendationsManufacturers recommendations• Initial integrity and soundnessInitial integrity and soundness• Age of equipmentAge of equipment• Working environment e.g. wet , hot, dustyWorking environment e.g. wet , hot, dusty• Frequency and duration of useFrequency and duration of use• Foreseeable abuse of equipmentForeseeable abuse of equipment• Effects of any modifications or repairsEffects of any modifications or repairs• Analysis of records of previous maintenanceAnalysis of records of previous maintenance

Effects of Electric ShockEffects of Electric Shock

Muscular contractionsMuscular contractions Respiratory failureRespiratory failure Fibrillation of the heartFibrillation of the heart Cardiac arrestCardiac arrest BurnsBurns Can result in secondary injuries e.g. Can result in secondary injuries e.g.

falls from height or muscle tearsfalls from height or muscle tears

First Aid for Electric ShockFirst Aid for Electric Shock

Break contact between current and Break contact between current and victim either by switching off or victim either by switching off or removing victimremoving victim

Ensure rescuer does not come into Ensure rescuer does not come into contact with anything live e.g. victims contact with anything live e.g. victims skinskin

Artificial respiration should commence Artificial respiration should commence immediately and continue until the immediately and continue until the victim recovers or qualified medical victim recovers or qualified medical aid intervenesaid intervenes