Unit 11 Elctrical Hazards Control

8/8/2019 Unit 11 Elctrical Hazards Control

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Unit 11:

Electricalhazards and

control


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Aims: understand:

The hazards and risks associated with the use ofelectrical equipment and systems operating at mains

voltages;

The measures that should be taken to minimize therisks.

Specific outcome.

Be able to:

Identify the hazards and evaluate the consequentialrisks from the use of electricity in the workplace;

Advice on the control measures that should be takenwhen working with electrical systems or using

electrical equipment.

Reference:

Maintaining Portable and Transportable Electricalequipment (HSG107), HSE Books.

Electricity at Work -Safe Working Practices (HSG85), HSE Books.

Tuition time: 3 hours.


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hazards and control 1.2 Basic Circuitry 1.2.1 Video: Introduction to electricity 1.3 Principles of electricity Question 1 1.3.2 Voltage and current 1.3.3 Relationship between voltage, current and resistance

Question 2 Question 3 Question 4 1.3.4 Conductors, insulators, and electron flow Question Question 5 1.4 Hazards of electricity Question 6 Question 7 1.4.1 First-aid treatment for electric shock 1.4.2 Other ways in which electricity can cause harm to humans Question 8 1.4.3 Other hazards associated with electricity - Fire hazards 1.4.4 Other hazards associated with electricity - Explosion hazard 1.4.5 Other hazards associated with electricity - static electricity 1.4.6 Damage to electronic components 1.4.7 Video: Dangers of Electricity Question 9 Question 10 1.5 Portable electrical equipment 1.5.1 Portable electrical equipment 1.6 Control measures 1.6.1 Selection and suitability of equipment 1.6.2 Fuses as control measures 1.6.3 Circuit breaker 1.6.4 Earthing Principles as control measures 1.6.5 Isolation as control measures 1.6.6 Live working 1.6.7 Reduced low voltage systems as control measures 1.6.8 Residual current devices as control measures 1.6.9 Double - insulation as control measures Question 11 1.7 Inspection and maintenance strategies 1.7.1 Competence to test 1.7.2 Test equipment 1.7.3 Frequency of inspection and testing 1.7.4 Test parameters 1.7.5 Records of inspection and testing 1.7.6 On-site Testing 1.7.7 Other factors to consider Question 12 Question 13 2.0 Summary


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1.2

Basic Circuitry

Acircuitis an unbroken loop of conductive material that allowselectrons to flow through continuously without beginning or end.

If a circuit is "broken," that means its conductive elements no longerform a complete path and a continuous electron flow cannot occur in it.

The location of a break in a circuit is irrelevant to its inability to sustain

continuous electron flow.Any break, anywhere in a circuit prevents electronflow throughout the circuit.

1.3

Principles of electricity

Most places of work, whether they are industrial units, smallbusinesses, shops, offices, hotels or catering establishments will involve people

working in an environment on or near electricity. Almost all of industry's

motive power is derived from electricity.

When misdirected or misused, electrical energy can severely burn, injure

or kill individuals. Many hundreds of accidents each year are caused by

electricity and about 25% of those involve portable electrical appliances. Whilst

only about 3% of all industrial accidents are electrical, nearly 7% of all

industrial fatalities are caused by electricity; this suggests that an electrical

accident is approximately 20 times more likely to prove fatal than most othertypes ofaccident.


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1.3.2

Voltage and current

We need more than just a continuous path (circuit) before a continuousflow of electrons will occur; we also need some means to push these electronsaround the circuit.

Just like marbles in a tube or water in a pipe, it takes some kind of

influencing force to initiate flow. With electrons, this force is the same force at

work, as in static electricity - the force produced by an imbalance of electric

charge.

When the electrons are poised in that static condition (just like water

sitting still, high in a reservoir), the energy stored there is calledpotential

energy, because it has the possibility (potential) of release that has not been

fully realized yet.

When you scuff your rubber-soled shoes against a fabric carpet on a dry

day, you create an imbalance of electric charge between yourself and the carpet.

The action of scuffing your feet stores energy in the form of an imbalance of

electrons forced from their original locations.

If this charge (static electricity) is stationary, you won't be aware that

energy is being stored at all. However, once you place your hand against a

metal doorknob (with lots ofelectron mobility to neutralize your electric

charge), that stored energy will be released in the form of a sudden flow ofelectrons through your hand, and you will perceive it as an electric shock.

This potential energy, stored in the form of an electric charge imbalanced

and capable of provoking electrons to flow through a conductor, can be

expressed as a term called voltage, which technically is a measure of potential

energy per unit charge of electrons, or something a physicist would call specific

potential energy. Voltage is also called 'electromotive force ', or E .M .F. )

Because voltage is an expression of potential energy, representing the possibility orpotential for energy release as the electrons move from one "level" to another, it is alwaysreferenced between two points, sometimes this is called 'potential difference'.


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1.3.3

Relationship between voltage, current and

resistance

If two points with a potential difference are connected by a conductivematerial, this potential for work is measured as a voltage.

When connected as described, the surplus electrons at the negatively

charged terminal will attempt to flow to the area of deficit or positively chargedterminal; this electron flow is called an electric current.

The amount of opposition to this flow will be determined by the nature of

the conductive material forming the current path and is known as its resistance.

1.3.4

Conductors, insulators, and electron flow

The electrons of different types of atoms have different degrees offreedom to move around.

With some types of materials, such as metals, the outermost electrons in

the atoms are so loosely bound that they chaotically move in the space between

the atoms of that material by nothing more than the influence of room-

temperature heat energy.

Because these virtually unbound electrons are free to leave theirrespective atoms and float around in the space between adjacent atoms, they areoften calledfree electrons.

In other types of materials such as glass, the atoms' electrons have very

little freedom to move around. While external forces such as physical rubbing

can force some of these electrons to leave their respective atoms and transfer to

the atoms of another material, they do not move between atoms within thatmaterial very easily.


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This relative mobility of electrons within a material is known as electric

conductivity. Conductivity is determined by the types of atoms in a material (the

number of protons in each atom's nucleus, determining its chemical identity)

and how the atoms are linked together with one another.

Materials with high electron mobility (many free electrons) are called

conductors, while materials with low electron mobility (few or no freeelectrons) are called insulators.

Here are a few common examples of conductors and insulators:

Conductors:

Silver. Copper. Gold. Aluminium. Iron. Steel. Brass. Bronze. Mercury. Graphite. Dirty water. Concrete.

Insulators:

Glass. Rubber. Oil. Asphalt. Fibere Glass. Porcelain. Ceramic. Quartz. (Dry) cotton. (Dry) paper. (Dry) wood. Plastic. Air. Diamond. Pure water.


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1.4 Hazards of electricity The Mechanism of

Electric Shock.

Two life-supporting functions of the body can be affected and in some cases

disabled by electricity, namely the circulatory and the respiratory systems.

The respiratory control signal is passed from the brain to the diaphragm. The

diaphragm comprises a large flat muscle situated immediately below the base of

the lung and this muscle initiates the breathing cycle.

The mechanisms which control the body's circulatory and respiratory functions

are electro-chemical systems, situated in the upper torso. The most dangerous

path for an electrical current to take is through the body's upper trunk. This

could be as a result of an electric shockresulting from hand to hand or hand to

foot contact.

The severity of an electric shockwill depend on the magnitude and duration ofthe current which flows.

Much will depend upon the electrical resistance of the body. Most of the human

body's resistance to the flow of electric current is provided by the skin. The

actual value of this resistance is dependent on the skin's thickness, its moisture

content and the applied voltage. All of these are personal, climatic andenvironmental variables.

The resistance figures quoted below represent average values and are given to

emphasise the uncertain degree of low voltage hazards.

At mains voltage (240 V), the body's resistance allows a current of 240 milli-

Amperes (mA) to flow. This level ofcurrent would prove fatal if the contact

occurred for longer than a few milliseconds.

At 90 V (the voltage likely to be present on, for example, the faulty metal caseof a piece of portable electrical equipment, with a phase to earth short circuit

and before fuse failure), the body's resistance increases carrying a potentially

fatal current of 45mA.

It is generally accepted that a potential below 50 V ac extra low voltage (ELV)

is unlikely to prove fatal. The body may only pass a current in the region of

12.5 mA and no permanent harm will be done.


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The experience may still prove painful and cause a consequential non-electrical

injury. In some circumstances related to age, health and environmental

conditions even ELV may be fatal to humans. A farm or domestic animal can

be killed by ELV as low as 25 V.

Effects of Electric Current.

The human threshold ofperception of a 50 Hertz electric current (UK mainsfrequency) is approximately 1.5 mA; below this level, it is unlikelythat any sensation ofcurrentflow will be felt.

As the prospective current level increases, contraction of the muscles occurs

resulting in the person gripping the points of contact and being "held-on".

A further small increase in current will cause the respiratory muscles and heartmuscles to be affected.

At 50 mA, ventricular fibrillationmay occur (i.e. the heart"flutters" rapidly and no longer serves as a pump). This can result in death.

A current of100 mAis likely toprove fatal.

Relatively small amounts ofcurrent flowing through the body will cause serious

damage. This current is related to the applied voltage, the current path through

the body and the resistance of this path is also time-related.

The fundamental aim ofelectric shockprevention measures is to ensure that thehuman body is subjected to the minimum voltage and current for the shortest

period of time.


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In summary: the factors affecting the severityof the shock are

duration; path ofcurrent; size ofcurrent; voltage; frequency; personal susceptibility; environment; possible proctection afforded by PPE.


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1.4.1

FirstFirstFirstFirst----aid treatment foraid treatment foraid treatment foraid treatment for

electric shockelectric shockelectric shockelectric shock

If possible, the electricity supply should be switched offas appropriate - removing the plug, switching off at the mainfuse box, etc.

If this is not possible, the victim must be moved as quicklyas possible away from the source ofpower and this must beachieved without endangering anyone else

The victim should be pulled away from the source by

means of a non-conducting implement such as a woodenbroom handle (dry) or a sheet or garment used as a lasso.

If very high voltages are involved, such improvisation maybe very dangerous to the rescuers; for example if the victim isfound slumped over equipment in an electricity sub-station,extreme care needs to be exercised.

If the victim is unconscious and has stopped breathing,artificial resuscitation must be started immediately andcontinued, even if the victim appears to be dead.

Help should have been called at the earliest opportunity and in many cases could be the very first resc

ue action of all.


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1.4.2

Other ways in which electricity can cause harm to humans

Damage to the nervous system.

An electrical shock can cause serious interference to the body's

own electrically-based brain/central nervous system.

Burns.

Apparently small entry and exit marks where the currententered and left the body may hide awful internal burns which can

fester and lead to septicaemia and may be hard to treat, perhaps

requiring amputation or plastic surgery.

Secondary effects.

These include falls, which may turn a relatively minorelectrical shock into a serious accident, loss ofcontrol of equipment

and so on.


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1.4.3

Other hazards associated with electricity - Fire hazards

Fires.

A large percentage of fires are of an electrical origin, caused by one ormore of the following:

Sparks.

A spark arises from a sudden discharge through the air between twoconductors, or from one conductor to earth. The current produced is usually

small so that serious fires are unlikely unless explosive gases or vapors arepresent, or highly flammable material is in contact with the conductor.

Arcs.

An arc is a much larger and brighter discharge where the current flowmay be hundreds of amps. It usually arises when a circuit is broken or when a

conductor melts or fractures leaving a gap, across which current continues toflow. When an arc is established, the air in the vicinity becomes ionized and

forms a conductor which may allow current to flow to a nearby metal

framework. Any combustible material in the vicinity could therefore lead to a

fire.


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Short circuits.

Ashort circuit is formed when the current finds a path from the

outward conductor wire to the return wire other than through the equipment to

which it is connected. The current flow may be large because of the low

resistance of the leads, and arcing often occurs at the contact between the

conductors. Insulation may therefore be burned and set fire to adjacent

flammable material. Batteries have a low internal resistance and can give rise to

very large currents under short circuit conditions, causing a large arc from

which molten metal may be splashed.

Over load of old wiring.

Wiring must not be overloaded, otherwise it will overheat and theinsulation will be damaged. This may lead to a short circuit. At some place inthe conductor, or more likely at connection points.

The insulation of wiring which has been in use for a number of years

tends to become brittle and, where alterations and additions are required, the

cable must always be checked by a competent electrician and replaced

completely if there are indications of failure of the insulation.

Installations should be protected against overloadingand shortcircuits by fuses or circuit breakers.


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In addition to the examples of electrical good practice which we will discuss in this unit,

you will appreciate that control ofwaste material and preventing the build-up of rubbishalso play an important part in averting workplace fires.

1.4.3 Other hazards associated with electricity - Fire hazards 1.4.4 Other hazards associated with electricity - Explosion hazard 1.4.5 Other hazards associated with electricity - static electricity 1.4.6 Damage to electronic components 1.4.7 Video: Dangers of Electricity Question 9 Question 10 1.5 Portable electrical equipment 1.5.1 Portable electrical equipment 1.6 Control measures 1.6.1 Selection and suitability of equipment 1.6.2 Fuses as control measures 1.6.3 Circuit breaker 1.6.4 Earthing Principles as control measures 1.6.5 Isolation as control measures 1.6.6 Live working 1.6.7 Reduced low voltage systems as control measures 1.6.8 Residual current devices as control measures 1.6.9 Double - insulation as control measures Question 11 1.7 Inspection and maintenance strategies 1.7.1 Competence to test 1.7.2 Test equipment 1.7.3 Frequency of inspection and testing 1.7.4 Test parameters 1.7.5 Records of inspection and testing 1.7.6 On-site Testing 1.7.7 Other factors to consider Question 12 Question 13 2.0 Summary


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1.4.4 Other hazards associated with electricity - Explosion hazard

The main causes of electrically-induced explosions are listed below:

(i) In situations where flammable gases or vapours are present so that

a spark could ignite an event. In such environments all electrical

equipment should be flame-proof.

(ii) Where electric arcing takes place in a confined space causingintense local heating with a consequent bursting of the enclosure

by the expansion of trapped air.

(iii) Rechargeable batteries emitting hydrogen when being charged,

giving rise to an explosive atmosphere. Such operations should be

carried out in a well-ventilated area, the temperature of which

should not exceed 18

o

C.

There is one further very important electrical cause of firesand explosion (and other hazards) which we need to discuss, and

this is static electricity.


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1.4.5 Other hazards associated with electricity - static electricityStatic electricity is trapped electricity: either trapped on an insulating

material or trapped on a conducting material which is, in turn, insulated from

the rest of the environment.

An example of the latter might be the electrostatic charge which builds

up on a metal shopping trolley which, because of the insulating wheels and

floor, remains trapped on the trolley until you touch a metal handrail etc which

does have a contact to earth.

Thus, the key to the control of static electricity is to provide a conducting

path so that the charge will not continue to build up but will flow away to earth

without causing harm.

Many different industrial processes are liable to generate electrostatic charges:

Flow of liquid through pipelines. Movement of material (animal feed stocks, coal, granulated

plastic, custard powder) along conveyors, sliding down a

chute into storage bins, sliding through discharge valves and

so on.

Transfer of powered material by blowing (this is often usedin the bulk transfer of powdered/fine grained material).

The movement of vehicles and people on insulating floors.

1.4.6 Damage to electronic componentsIn addition to the fire/explosion hazards which are our main concern in

this unit, the sudden discharge of static electricity can damage electronicequipment/components - circuit boards, control panels and so on.

During the manufacture, assembly and operation of such vulnerable

equipment, safeguards will need to be taken to prevent static charges from

building up.


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1.5 Portable electrical equipment

Portable appliances.

Portable appliances are defined as:

anything with a plug on it; anything capable of being readily disconnected from and

reconnected to the electrical system.

In practice, what constitutes a "portable appliance" is open to debate

because the distinction is largely academic.

The electrical system is required to be constructed and maintained in

such a way as to prevent danger arising, so far as is reasonably practicable.

Any electrical appliance, whether portable or not, is part of that system

and must therefore be safe at all times.

The reasons why more emphasis should be given to portable appliances

(however defined) include:

Increased likelihood of mechanical damage during movement ofthe equipment.

The variety of potential work environments, particularly in the caseof equipment used outdoors.

The need for identification so as to ensure that equipment has beensubjected to appropriate tests and examinations.

For ease of traceability and to assist record keeping.

Another consideration is whether equipment is physically moved during the

process of use, for example a vacuum cleaner, or remains in a static position,

e.g. a microwave oven. This factor must be taken into account when decidingthe frequency of electrical test and examination.


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1.5.1 Portable electrical equipment

There is no specified time schedule for inspection or testing ofelectrical equipment.

What you, or an external contractor, need to decide is whatequipment you have, where it is used, how often and how likely is it to

become defective in those circumstance.

The UKHealth and Safety Executive have been concerned in the

past that wrong advice on this was being given by some service providersso published IND(G)236L: Maintaining Portable Electrical Equipmentin Offices and Other Low Risk Environments. Updated in 1996 and isavailable from HSE Books.

For industrial premises, the information in IND(G)236L is a usefulstarting point for you to begin your electrical risk assessment and planappropriate inspection, testing and maintenance.

Nearly a quarter of all reportable electrical accidents involve portableequipment.

Most of these accidents result in electric shock; others result in fires,often caused by faulty leads to appliances. A major cause of suchaccidents is failure to maintain the equipment.

The likelihood of accidents occurring and their severity will vary,depending on the type ofelectrical equipment, the way in which it isused and the environment in which it is used.

One high risk situation is the use of Pressure water cleaner outside,powered by 240volt electrical supply, with the cable trailing on theground where it can be damaged by vehicles and other equipment, and

where surface water is present.


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Damage to the cable or other parts is likely to result in the operator orothers receiving an electric shock.

Similar risks result when other electrical equipment, such as drillsand portable grinders, are used in a harsh and sometimes wetenvironment, such as on a construction site where there is a highprobabilityof mechanical damage.

Lower risks result from floor cleaners or kettles, which are generallyused in a less hazardous environment, e.g. offices and hotels, but can besubject to intensive use and wear. This can eventually lead to faults

which can also result in shock, burns or a fire. Other common accidentcauses are:

The use of unsuitable equipment: e.g. flexible cable beingdragged through areas where oils, greases or solvents arepresent. In these areas, a cable should be selected which has asheath resistant to those chemicals.

Use of defective equipment: e.g. badly-made joints in

flexible cables which can expose bare live conductors. Operatorsshould be instructed never to make their own repairs, never touse defective equipment, to withdraw it from use and not re-useit until repaired and checked by a competent person.

Misuse of equipment: e.g. attempting to service equipment

without disconnecting it from the electricity supply rather thanwithdrawing it from service for inspection by a competentperson.

Inadequate maintenance: e.g. no system of regular

inspection or testing and repair of equipment. Regularinspections of portable equipment are particularly importantdue to the hard use which it often suffers.

We should note that the hazards associated with hand-held tools

are particularly significant as the hand is likely to be gripping the toolwhen in operation, making it more difficult - or impossible - for theoperator to let go in the event of a fault.


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1.5 Control measuresHazards involved in the use of work equipment may result from

inadequate design, construction, installation, selection, maintenance

or use of electric equipment.

An electrical system may be dangerous because it contains a

fault or it is being used in a dangerous manner.

Frequently, those working on or near systems are not fully

aware of the dangers.

The main techniques of controlling and minimising risks

associated with electricity are the correct selection, installation and

maintenance of equipment, the insulation of live parts and theretention of the electric current in the correct place at the correctly-

rated value.

Control measures include:

Selection and suitability of equipment. Suitably-trained competent users. Fuses. Earthing. Isolation. Reduced low voltage systems. Residual current devices. Double insulation.

Inspection and maintenance strategies:o user checks;o formal inspection and tests;o frequency ofinspection and testing;o records ofinspection and testing;o inspection and testing of Portable Appliance Testing

(PAT).


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1.6.1 Selection and suitability of equipment

The selection and suitability of equipment is the first consideration. Why

use a 240v cabled drill whilst installing an external satellite dish when you

could use a battery-operated drill?

1.6.2 Fuses as control measures

Control of over-current.

There are two definable types of over current: overload and

fault current.

Overload.

This occurs in a healthy circuit where equipment has beenmechanically overloaded or an excessive number of applianceshave been added to a system. The consequences of overloadusually involve overheating and, if uncontrolled, fire.

Overload protection relies upon the detection of excesscurrent and disconnection when predetermined time limits havebeen exceeded. Two detection methods are employed:

(a) thermal: using wire fuses;

(b) magnetic: using circuit breakers.

The two methods may be combined for certain conditions. Itwill be appreciated that the current level for overloaddisconnection will always be in excess of the normal workingload. This will usually be measured in terms of amps andinevitably will be greater than human electric shock tolerancewhich is measured in thousandths of an amp (mA).


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Fault Current.

When a fault current arises from phase-to-earth or phase-to-neutral, a low resistance "fault loop impedance" will cause

sufficient over-current to flow, to melt a fuse or trip a circuitbreaker (i.e. disconnect the supply).

Note - for the purposes of this explanation, the term 'impedance'is synonymous with electrical resistance.

1.6.3 Circuit breaker

A circuit breaker is a mechanical device in the form of a

switch that automatically opens if the circuit is overloaded.

These types of protective devices should be chosen so theirrating is above the operating current required by the equipment but

less than the current rating of the cable in the circuit.


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1.6.4 Earthing Principles as control measures

Earthing provides an electrical distribution system with basic safety

characteristics.

Initially, it could be supposed that an unearthed system would be safer than itsearthed equivalent.

Most electric shocks that people receive are between a live conductor and earth;

these shocks would not be possible on an isolated (unearthed) system. For this

reason, isolated systems with special transformers are used locally in very

hazardous surroundings such as laboratories or workshops where electronic

equipment with earthed cases is opened up for repair. This is a specialised

condition and the isolation feature is continuously monitored.

On public electricity networks, however, there would beno guarantee that an isolatedsystemwould remainunearthed indefinitely.

At some stage, an accidental connection would occur either on a damaged

underground distribution cable or with a faulty appliance on private premises.

One such occurrence alone would not be noticed or cause a direct problem;

however, the inherent safety of an isolated system would no longer exist.

Inevitably, a second earth fault would arise and an uncontrolled current would

circulate through earth via the faulty connections. This situation would probablycause a fire.

Public supply systems are therefore earthed and it is now common practice to

improve the earth/neutral bond by creating multiple connections throughout the

supply network. This is known as Protective Multiple Earthing (PME).

Interconnection ofearth and neutral paths provides the lowest possible fault

impedance. The consequence of a PME connection is that both fault and loadcurrent are shared between earth and neutral in proportion to their respective

resistances.

As the proportionate share of this current is an unknown factor, interconnection

ofearth and neutral is only permitted on the supply authority's system since it is

dangerous to make any earth/neutral connection within a consumer's

installation.


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1.6.5 Isolation as control measures

With every electrical system, provision must be made for switching off

the supply.

It is essential to provide suitable means first for cutting off the supply and

secondly for isolation. This is the cornerstone for a safe system of workbased

on de-energised plant.

Isolation is the disconnection and separation of the electrical equipment

from every source of electrical energy in such a way that both disconnectionand separation are secure.

There are various forms ofisolation involving locking-off or removal ofparts of the circuit.

The need to ensure that, if at all possible, the circuit is dead when beingworked upon leads us on to situations where this is not possible, and liveworking must be undertaken.


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1.6.61.6.61.6.61.6.6Live workLive workLive workLive workinginginging

The first precaution is to ensure that live working is indeed unavoidable -

it is not enough for management to say that they did not want to stop

production. There must be absolutely compelling reasons why live working hasto be undertaken.

... wwwwork on or near liveelectrical equipmentshall only take place if it isunreasonable for the equipment in all circumstances to be dead, reasonablein all circumstances for work to be carried out on or near the equipment whenit is live and suitable precautions have been taken.

Regulation 14 ofThe UK Electricity at Work Regulations 1989

Once this live working need has been established, then the engineers

working on the live system must be protected by an appropriate system ofwork:

Exposed live parts kept to a minimum, both in terms of the timeof exposure and the actual amount of live material that is

exposed.


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Use of protective equipment such as insulated tools, protective

clothing (including gloves and footwear) and other protective

devices such as insulated mats.

Use of accurate circuit diagrams and information. Permit-to-works may be required (a permit-to-work is a formal

written system of work with each step being approved before

the next step is commenced).

A competent person on stand-by may also be required.

1.6.7

Reduced low voltage systems as control measures

Where environmental conditions are harsh, as on construction sites or in

areas that are wet, the use of safe or low voltages is advisable and an excellentway of reducing shock risk.

Special 110 V appliances are used which operate from 55-0-55 V centre-

tap earthed transformers. These appliances may be Class 1 or Class 2

construction.

Rechargeable battery operated tools.

In addition to safety, these have the advantage that no supply connectionis required and leads are avoided. These tools require regular maintenance to

ensure good battery connections. Batteries should be handled with care and not

carried with terminals unprotected in pockets or in tool boxes.


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Reduced low voltage systems.

These are most appropriate for most industrial applications but the risk of

cable damage must always be taken into account. Transformers are required

either to supply individual tools or for fixed circuitry. Plugs and sockets are

normally colour-coded yellow.

Supplementary protection may be given to the user with the use of 30

mA RCD protection. Any socket outlet which may reasonably be expected to

supply portable equipment outdoors should have supplementary RCDprotection. This applies to all types of equipment.

1.6.7Residual current devices as control measures

No electro-mechanical device can be 100% reliable. An RCD relies upon

moving parts and speed of contact separation. For this reason, a sensitive RCD

may only be used to provide supplementary personal shock protection.

The primary protection against contact with live parts must be by way of

insulation and appropriate mechanical protection. Supplementary shock

protection may then be added with an RCD which will disconnect 30 mA in

200 mS (milli-seconds) equivalent to 0.2 seconds and 150 mA in 40 mS (0.04

seconds).

Higher rating may be used to give protection against fire or large earth

faults in circumstances where there is an inherent earth leakage associated withequipment. Over-sensitive operation is not desirable. In some cases rapid, low

fault-current disconnection may be inconvenient or even introduceconsequential dangers.

A residual current device may be combined with an over current mechanism in

which case the combined unit is termed a Residual Current Breaker with Overloadprotection (RCBO).


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1.7

Inspection and maintenance strategies

An on-site judgement must be made to take into account the conditions of

service and type of equipment. Two levels of regular inspection are suggested.

Basically, a frequent visual check by the user of the equipment should be

undertaken. The intended user requires some basic instruction to know what to

look for.

The physical inspection.

The most important and relevant test is the visual inspectionsince approximately 80% of equipment defects are found at this first

stage. A detailed physical inspection by a competent and

conscientious person will make a significant contribution to hazard

elimination.

Typical hazards may include:

Incorrectly wired plugs. Loose plug-top connections. Wrong value fuses or fuses replaced with a metal foil

or bar.

Plug cord grips not gripping the cord outer sheath. Damaged flexible cord. Unsafe cable joints. Damaged case-mounted components (e.g. fuse-

holders, voltage selectors, neon indicators, etc).

All physical defects must be corrected at this stage, before any

electrical tests are attempted. Unless a cable is damaged near to its

end when it may be shortened, all flexible cords which show any sign

ofdamage should be replaced, since cable repairs and joints are

unlikely to meet the stringent safety standards required.


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1.7.1

Competence to test

All persons who undertake work involving electricitymust be competent to prevent danger arising from that work.

Those being considered for competence in testing portable

equipment should have practical experience or adequateknowledge of:

(a) the principles of electricity together with a soundappreciation of the source and nature of electricalhazards;

(b) the precautions required to avoid danger;(c) whether it is safe for testing to continue following an

abnormal result;

(d) the relevant safetystandards;

(e) the hazards which may arise because of the testinglocation;

(f) the operating principles of the test equipment andthe unit under test;

(g) appliance testing and the use of test equipment;

(h) the interpretation of test results;

(i) the correct frequencyof testing.


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1.7.2 Test equipment

Each of the following tests may be carried out by a dedicated testinstrument. However, to ensure that the tests are conducted in a safesequence, the use of a Portable Appliance Tester (PAT) is stronglyrecommended.

The PAT will conduct each test using the correct test voltages andcurrents in a sequence that will ensure that if a failure occurs, there will

be no danger to the test person.

A variety of PATs are available, and a range of features are offered.Displays may be analogue or digital, and while some units offer manualoperation (i.e. select a test by operating a switch, then press the test

button), others are fully automatic and once initiated, will automaticallyrun through the complete sequence of tests, stopping if any one of thetest registers "fail". Some fully automatic testers will store hundreds ofresults that can be downloaded onto a computer database.

The type and extent of tests are a matter of judgment by thecompetent operative. Guidance must be taken from manufacturers' typetests, PAT equipment suppliers' instructions and only after suitabletraining.

Extreme care must be taken with highvoltage flash testing. This

may be unnecessary unless an appliance has been completely overhauledand full manufacturers' test procedures are necessary. Flash testing ishazardous and may cause damage to sensitive equipment.


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1. The unit under test should never be touched during thetest process.

2. During current consumption tests, the unit under testwill have normal power applied and will therefore operate inthe usual manner. All machinery guards should be in placeand all cutting blades and boring bits should be removed

before testing begins. Portable tools may need to be securedto prevent them moving across the test bench when power isapplied.


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1.7.3 Frequency of inspection and testing

The following is a suggestion for the frequencyofinspections, but these must be adjusted to suit the conditions of

use.

Business Use External Visual Check Full Electrical Test

Equipment hire. Before issue and after return. Before issue.

Construction. Daily. 3 months.

Industrial. Before use. 6 months.

Commercial and office. 36 months. 12 months.

Premises used by the public. 36 months. 12 months.

Further guidance can be found in EEA recommendationsfor periodic safetychecks for business equipment (available fromthe EEA).

The underlying principle regarding frequencyof testing isthat duty-holders (i.e. the person who has the equipment "withintheir control") should decide upon the frequencyof testing basedon the following criteria:

(a) the type ofenvironment in which the equipment

is used (i.e. indoors, outdoors, hazardousatmospheres, construction sites, etc)

(b) the conditions of use and hence the roughnesswith which it is handled (e.g. a hand-held electricdrill will be more roughly used in the company'sengineering workshop than in the developmentlaboratory).


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If the testing is being conducted for a non-technical thirdparty, the duty holder should discuss the frequencyof testingwith the competent test person when the initial surveyofequipment is being carried out.

Should the electrical equipment or tools be held in a centralstore between periods of use, they should be inspected on issueand on return in addition to the periodic safetytest.

Any item that develops a fault during use should be

immediately disconnected, clearly labelled with the suspectedfault and returned for repair. A suitable label is shown below.

FAULTY - DO NOT USE

EQUIPMENT TYPEMODEL SERIAL NO

FAULT DESCRIPTION

REPORTED BY DATE

The label should not be of the same colouras the "safetytest /pass" label; a red backgroundwith a white or black legend is recommended.


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1.7.4 Test parametersThe regular simple visual check should consist of the following:

Visual check for signs ofdamage to the equipmentand its supply cord.

Check lead and plug and cord-grip at both ends. Check any extension leads.

If any faults are found, the equipment should be withdrawn from service for

repairs followed by a full test.

The objective of a full electrical inspection is to ensure that the safety

measures designed into equipment are still effective and are liable to remain

effective until the next scheduled test date.

It may therefore be argued that the "type approval" tests conducted by the

manufacturer could be used as a reference for the routine periodic safety tests.

The argument is valid providing it is realised that certain tests during

manufacture are conducted with some circuit components removed to prevent

them sustaining damage.

In addition, all type approval tests are conducted in a specifically-

designed area to ensure the safety of the test person.

It is therefore necessary to modify the manufacturers' type approval tests

when conducting routine safety testing, to ensure that sensitive equipment is not

damaged and so that the tests may be conducted in safety in a variety of

environments.

Such considerations are encompassed in the design of specially-producedPortable Appliance Testers (PATs).


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1.7.5Records of inspection and testing

Record Keeping.

With electrical fixed plant, the duty holder should keep an inventory of

equipment to be tested and a repair history.

Records of all portable/transportable equipment test results should bekept in a form that will allow their inspection and reproduction when required.

The records may be kept in the form of a paper copy if the quantity of

equipment to be tested is small. Each test result should be recorded as the testsprogress and care should be taken to reproduce the test figures accurately.

When the volume of equipment to be tested is high, it may be more

convenient to use a computer database that can readily accommodate the large

amount of data involved. The use of a database will reduce the time required to

manage the work and allow the testing function manager to automatically

remind the equipment user that subsequent routine testing is due.

Modern portable appliance test equipment will automatically download

the test results to a computer workstation and specially written software will

hold the records, forecast future routine work due and hold an inventory of

equipment against locations, etc. Should a database be used, the test data should

be in a readily reproducible form and password protected.


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Irrespective of the recording system used, a copy of the last test figures

recorded should be available to the test person when conducting subsequent

tests, so that a judgement may be made regarding the significance of any

variation with the new test results.

The users of the portable appliances will require certain information toallow the duty holders to fulfill their statutory responsibilities.

The test person should fix a label to equipment that has been successfully

tested, giving the following information:

(a) The date tested;

(b) The identity of the test person;

(c) The date of the next test.

Such a label will allow the duty holder to install a management system

whereby no electrical item may be used outside of the two dates shown on the

safety test label. Items that fail the safety tests should be immediately

withdrawn from service for repair.

A suitable "PASS" label is shown below.

ELECTRICAL SAFETY TESTED

DATE TESTED NAME

DATE NEXT TEST DUE

A label colour of white lettering on a green background would visually indicate a"safe condition".


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1.7.6 On-site TestingThe on-site location may not be under the direct control of the test person

and thus may present extra hazards compared with a purpose-built workshop.

Where such dangers cannot be satisfactorily eliminated, the testing

activity should be transferred to a more suitable location or preferably to aproperly-designated test area.

Test persons have a legal responsibility to conduct the testing process in a

manner that ensures both their own safety and the safety of all others who maybe in the vicinity.


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1.7.7

Other factors to consider

Electrical Installations in Buildings.

The usual distribution system in industrial and commercial

buildings will be three phase 240/415 V. This supply is potentially

lethal and can cause fires. The duty holder has an obligation to

ensure that new work and maintenance is carried out by competent

electrical personnel.

Permanent records of all electrical activity should be

retained for future reference.

Temporary installations.

Particular concern should be given to temporary

installations. No relaxation ofsafety rules or protection is

permissible. Temporary installations must be designed to at least

the same standard as permanent installations and must be inspectedand tested more frequently (i.e. every three months).

Strict control must be enforced to resist any temptation to

carry out an installation that is unprotected physically orelectrically.

Cabling and Wiring Systems.

There is a range of wiring systems, each of which hastechnical or commercial advantages for particular locations.

Competent advice should be sought before specifying a system.

There is no one common answer to every condition. Invariably,

more than one wiring system will be used in a building.

Factors which need to be considered when choosing a wiring

system are listed in the IEE Wiring Regulations and divided into

three categories.


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Environment.

This includes factors of ambient temperature and

climatic conditions. Hazardous locations must be taken

into account and the relationship with other engineering

services, pollutants or industrial activities.

Utilisation.

This includes occupational details and competence

of occupants to handle emergencies. Fire and explosion

risks may require special attention, taking into account

evacuation facilities.

Construction of buildings.

Levels of combustibility must be considered together with

life expectancy of the installation and maintainability.

Working on or near live electrical equipment should only

take place if it is unreasonable for equipment in all circumstances

to be dead.

1. ? True2. ? False

The most important and relevant test ofelectrical equipment is via a ......

1. ? Full physical inspection2. ? Visual inspections


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2.0 SummaryThis summary section will refer you back to the learning outcomes and summarise the notes.

Identify the hazards and evaluate the consequential risks from the use of electricity in

the workplace:-

Hazards of Electricity

Electric Shock. Fires Sparks Arcs Short circuits Overloading and old wiring ExplosionHazard Static Electricity

Advise on the control measures that should be taken when working with electrical

systems or using electrical equipment.

The main techniques of controlling and minimising risks associated with electricity are thecorrect selection, installation and maintenance of equipment, the insulation of live parts and

the retention of the electric current in the correct place at the correctly rated value.

Control measures include:

Selection and suitability of equipment. Fuses. Earthing. Isolation. Reduced low voltage systems. Residual current devices. Double insulation. Inspection and maintenance strategies:

o user checks;

o formal inspection and tests;o frequency ofinspection and testing;

o records ofinspection and testing;

o inspection and testing of Portable ApplianceTesting (PAT).

Electrical Hazards Congratulations

end of lesson reached


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Documents

Unit 11 Elctrical Hazards Control