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Be sure to properly label any connections you make and update them with any changes. Accidentally turning off the lights on your wife in the bathroom when you meant to disconnect the kitchen may lead to some choice words. New appliances come with their own electrical challenges, which is why many people choose to pay for the installation. If you're a true DIY-er, you can install a dishwasher without problems.

The dishwasher comes with two hook-up challenges: the wiring and the water and drain lines.

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That's why it's a good idea to choose a location near your sink. It will save you time and money. Your electric range may also require your electric prowess. You might find yourself replacing the oven bake element , which is a relatively simple project. You may also need to connect the cord.

The exact method you need to follow is going to depend on whether you have a 3- or 4-prong cord. Keep in mind that these large appliances carry heavy voltages, so read up on the safety tips. For instance, plugging a loose cord into a receptacle to check the fit can give you a deadly shock.

Don't do it. Why oh why do you have to buy a dryer cord separately? It's one of the great mysteries of home improvement, but it's a fact of life. Next time you need to install that new dryer, you'll be prepared after this tutorial. Understand Colors and Labeling Electrical wire has very convenient ways of telling you what it is. As you learn more about wiring, you'll realize just how often you need to know these things. Wire Size Matters It is critical in any wiring project that you match the gauge of the wire with the amperage rating of the circuit.

Installing an Outlet Many homeowners want to take care of the basic wiring needs for their house. Continue to 5 of 9 below. This course is available as a company sponsored event, delivered at a location, date and time which is mutually agreed. The fees for this event vary depending on the location, number attending and the level of training required and the degree of customisation. Please contact us to discuss your requirements. This course is available on demand and dates are available on application, please contact us to discuss your requirements.

The act of earthing connects together all metalwork, other than that intended to carry current, to the general mass of earth so that a dangerous potential difference cannot exist between different metal parts, or between metal parts and earth. Earthing: The IEE Regulations define earthing as the act of connecting the exposed conductive parts of an installation to the main earthing terminal of the installation.

This means the metalwork of an appliance or the metalwork of the electrical installation such as the conduit, trunking or metal boxes of the electrical system, all of which must be connected to the main earthing terminal of the installation. Circuit Protective Conductor CPC : This is a protective conductor connecting exposed conductive parts to the main earthing terminal.

It will be a green and yellow insulated conductor of appropriate size.

Introduction to Basic Domestic Electrics

Extraneous Conductive Parts: This is the structural steelwork of a building and other service pipes used for gas, water, etc. They do not form a part of the electrical installation, but may introduce a potential to the electrical installation. To eliminate this hazard we provide equipotential bonding. Equipotential Bonding: This is an electrical connection which maintains exposed conductive parts and extraneous conductive parts at the same potential. To do this, we connect a green and yellow insulated cable of appropriate size to all extraneous parts and connect this to the main earthing terminal of the installation.

By connecting to earth all metalwork not intended to carry current, a safe path is provided for any leakage currents which can be detected and disconnected by fuses, circuit breakers and RCDs. A good earth path, that is a low resistance earth path, will allow high fault currents to flow, which will cause ChH Overcurrent Protection All circuit conductors must be protected against overcurrent, that is, a current exceeding the rated value Regulation Fuses and circuit breakers provide overcurrent protection when situated in the live conductor.

They must not be connected in the neutral conductor. Overcurrent conditions arise because of an overload or a short circuit in the electrical circuit. Try writing out these definitions — just the essential bits to help you to remember them — for overcurrent, overload, short circuit current and a fuse. By definition an overload current occurs in a circuit which is carrying more current than it was designed to carry.

The excess current may be a result of too many pieces of equipment being connected to the circuit or because a piece of equipment has become faulty. An overload current will result in currents of two or three times the rated current flowing. This will cause the cable temperature to rise, leading to an increased risk of fire.

By definition a short circuit current occurs in a circuit as a result of a fault or damage to the circuit which could not have been predicted before the event. The short circuit current may be the result of a nail being driven through an energised cable, making contact with the live conductor and either the neutral or earth conductors. A short circuit current will result in currents hundreds of times greater than the rated current flowing. To avoid the risk of fire or electric shock, these overcurrents must be interrupted quickly and the circuit made dead.

Under fault conditions it will melt when an overcurrent flows, protecting the circuit conductors from damage. Semi-enclosed Fuses BS The semi-enclosed fuse consists of a fuse wire, called the fuse element, secured between two screw terminals in a fuse carrier. The fuse element is connected in series with the load and the thickness of the element is sufficient to carry the normal rated circuit current. This type of fuse is illustrated in Fig. The fuse element should consist of a single strand of plain or Figure 3. This type of fuse was very popular in domestic installations, but less so these days because of their disadvantages.

The fuse element is encased in a glass or ceramic tube and secured to end-caps which are firmly attached to the body of the fuse so that they do not blow off when the fuse operates. Cartridge fuse construction is illustrated in Fig. With larger size cartridge fuses, lugs or tags are sometimes brazed on the end-caps to fix the fuse cartridge mechanically to the carrier. They may also be filled with quartz sand to absorb and extinguish the energy of the arc when the cartridge is brought into operation. An MCB overcomes this problem since it is an automatic switch which opens in the event of an excessive current flowing in the circuit and can be closed when the circuit returns to normal.

An MCB of the type shown in Fig. The load current flows through the thermal and the electromagnetic devices in normal operation but under overcurrent conditions they activate and trip the MCB. The circuit can be restored when the fault is removed by pressing the ON toggle. The toggle switch can also be used to disconnect the circuit for maintenance or isolation or to test the MCB for satisfactory operation.

It may be high or low but to the Health and Safety Inspector, only low will be acceptable. Under fault conditions it will melt, protecting the circuit from damage. This is the basic principle of: a A. When a V supply is connected the secondary voltage will be: a 5. When connected to a V supply the transformer will deliver a secondary voltage of: a 2. Calculate the secondary voltage when connected to a V supply: a Under fault conditions it will melt, protecting the circuit conductors from damage.

Understanding the laws and regulations, the different types of installation and cabling and equipment used in electrical installation work. Regulations and Responsibilities In Chapter 1 of this Book we looked at a number of the regulations which control the electrotechnical industries. The Electricity at Work EAW Regulations are legally binding Regulations which concern all aspects of electrical systems, equipment and installations, which have been or are to be energised. The purpose of the Regulations is to require precautions to be taken against the risk of death or personal injury from electricity in work activities.

The IEE Wiring Regulations is a code of practice which is widely recognised and accepted in the UK and compliance with them is likely to achieve compliance with relevant aspects of the EAW Regulations If a contract specifies that the work will be carried out in accordance with BS , the IEE Wiring Regulations, then this would be legally binding and the IEE Wiring Regulations will then become a legal requirement of the contract. Figure 4. In the intervening years there have been many new editions and we are currently using the 16th Edition. British Standards having a BS EN number refers to a European harmonised standard and all such standards will become common throughout Europe.

Telephone or at www. Good communication is about transferring information from one person to another. How many hours or days did you spend on a particular job last week? How does your boss know how many hours of work you put in on that job, so that a charge to the customer for your time can be made? How much material did you use on that job last week? How does your boss know how much material you used, so that a charge to the customer can be made for it? Most electrical companies have standard forms which help them to keep track of time put in and materials used. When completing standard forms, follow the instructions given and make sure that your writing is legible — print if it makes your writing clearer.

Finally, read through the form to make sure that you have completed all the relevant sections. Time Sheets A time sheet is a standard form completed by each employee to inform the employer of the actual time spent working on a particular contract or site. This helps the employer to bill the hours of work to an individual job. It is usually a weekly document and includes the number of hours worked, the name of the job and any travelling expenses claimed.

Office personnel require time sheets such as that shown in Fig.

Description:

Job Sheets A job sheet or job card such as that shown in Fig. It gives the name and address of the customer, contact telephone numbers, often a job reference number and a brief description of the work to be carried out. This will depend upon what is normal practice for the particular electrical company. A careful record must then be kept on the daywork sheets of all extra time and materials used so that the client can be billed for the extra work and materials. A typical daywork sheet is shown in Fig.

Electrical Representative responsible for carrying out work Signature of person approving work and status e. Client Architect Signature Figure 4. This record is used to confirm that goods have been delivered by the supplier, who will then sent out an invoice requesting payment, usually at the end of the month.

The person receiving the goods must carefully check that all items stated on the Delivery Note have been delivered in good condition. Suppliers will replace materials damaged in transit, provided that they are notified within a set period, usually three days. It is best to check at the time of delivery if possible or as soon as possible after delivery and within the notifiable period. Electrical goods delivered to site should be handled carefully and stored securely until they are installed. Copies of Delivery Notes should be sent to Head Office so that payment can be made for the goods received.

Electricity Supply Systems The Electricity supplies to houses, shops, offices and small industrial consumers is nominally set at V single phase and V three phase. So, a domestic supply must be maintained by the supplier within V and V for single phase supplies and between V and V for three phase supplies. All EU countries agreed to change to these values from The frequency is maintained at 50 cycles per second over 24 hours so that electric clocks remain accurate.

The electricity supply to domestic, commercial and small industrial consumers is usually protected at the incoming service cable position by a A HBC fuse. You should also look at Fig. Five systems are described, but only three electricity supply systems are suitable for public supplies and we will, therefore, only concern ourselves with these three supply systems.

The neutral and protective conductors are separate throughout the system. All extraneous conductive parts of the installation, gas pipes, water pipes and any lightning protective system are connected to the protective conductor via the main earthing terminal of the installation. The arrangement is shown in Fig. It is more commonly referred to as protective multiple earthing PME.

All extraneous conductive parts of the installation, gas pipes, water pipes and any lightning protective system are then connected to the main earthing terminals. Thus phase to earth faults are effectively converted into phase to neutral faults. This means that for a domestic lighting circuit rated at 5 A or 6 A a maximum of 11 or 12 lighting outlets could be connected to each circuit. In practice, it is usual to divide the fixed lighting outlets into two or more circuits of seven or eight outlets each.

In this way the whole installation is not plunged into darkness if one lighting circuit fails. Lighting circuits are usually wired in 1. The loop-in method is universally employed with conduit installations or when access from above or below is prohibited after installation, as is the case with some industrial installations or blocks of flats. In this method the only joints are at the switches or lighting points, the live conductors being looped from switch to switch and the neutrals from one lighting point to another.

The use of junction boxes with fixed brass terminals is the method often adopted in domestic installations, since the joint boxes can be made accessible but are out of sight in the loft area or under floorboards. All switches and ceiling roses must contain an earth connection Regulation and the live conductors must be broken at the switch position in order to comply with the polarity Regulations A ceiling rose may only be connected to installations operating at V maximum and must only accommodate one flexible cord unless it is specially designed to take more than one One light controlled by one switch is called one-way switch control see Fig.

Fixing Positions of Switches and Sockets Part M of the Building Regulations requires switches and socket outlets in dwellings to be installed so that all persons, including those whose reach is limited, can easily reach them. This is shown in Fig. The guidance given applies to all new dwellings but not to re-wires. Pressing the plug top into a socket outlet connects the appliance to the source of supply. Socket outlets therefore provide an easy and convenient method of connecting portable electrical appliances to a source of supply. Socket outlets can be obtained in 15, 13, 5 and 2 A ratings but the 13 A flat pin type complying with BS is the most popular for domestic installations in the United Kingdom.

Each 13 A plug top contains a cartridge fuse to give maximum potential protection to the flexible cord and the appliance which it serves. Socket outlets may be wired on a ring or radial circuit and, in order that every appliance can be fed from an adjacent and convenient socket outlet, the number of sockets is unlimited provided that the floor area covered by the circuit does not exceed that given in Table 8 A, Appendix 8 of the On Site Guide and Figs 4. Radial Circuits In a radial circuit each socket outlet is fed from the previous one.

Live is connected to live, neutral and earth to earth at each socket outlet. The fuse and cable sizes are given in Table 8A of Appendix 8 of the On Site Guide but circuits may also be expressed with a block diagram as shown in Fig. Fuse or MCB 2. Fuse or MCB Figure 4. Where two or more circuits are installed in the same premises, the socket outlets and permanently connected equipment should be reasonably shared out among the circuits so that the total load is balanced.

This is because the maximum demand of current-using equipment in kitchens may exceed the rating of the circuit cable and protection devices. Ring and radial circuits may be used for domestic or other premises where the demand of the current-using equipment is estimated not to exceed the rating of the protective devices for the chosen circuit.

Ring Circuits Ring circuits are very similar to radial circuits in that each socket outlet is fed from the previous one, but in ring circuits the last socket is wired back to the source of supply. Each ring final circuit conductor must be looped into every socket outlet or joint box which forms the ring and must be electrically continuous throughout its length. The number of permitted socket outlets is unlimited but each ring circuit must not cover more than m of floor area. The circuit details are given in Table 8A, Appendix 8 of the On Site Guide but may also be expressed by the block diagram given in Fig.

Socket Outlet Numbers The Regulations allow us to install an unlimited number of socket outlets, the restriction being that each circuit must not exceed a given floor area as shown in Figs 4. These days most households have lots of domestic appliances and electronic equipment, so how many sockets should be installed? So, always install a double switched socket outlet unless there is a reason not to. Part 5 of the IEE Regulations tells us that electrical equipment and materials must be chosen so that they are suitable for the installed conditions, taking into account temperature, the presence of water, corrosion, mechanical damage, vibration or exposure to solar radiation.

These two types of cable are shown in Figs 2. Mineral insulated MI cables are waterproof, heatproof and corrosion resistant with some mechanical protection. These qualities often make it the only cable choice for hazardous or high temperature installations such as oil refineries, chemical works, boiler houses and petrol pump installations.

An MI cable with terminating gland and seal is shown in Fig.


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It is a fire resistant cable, primarily intended for use in fire alarm and emergency lighting installations. Its appearance is very similar to an MI cable in that it is constructed as a thin pencil size tube but the outer sheath is made from a robust thermoplastic material and is much easier to terminate than an MI cable. We will look at wiring enclosures in the next section but first let us look at the new wiring colours for all fixed wiring which came into force on the 1st April However, a warning notice must be fixed at the consumer unit or distribution fuse board which states: Caution — this installation has wiring colours to two versions of BS Great care should be taken before undertaking extensions, alterations or repair that all conductors are correctly identified.

However, for standard domestic circuits, Table 4. Table 4. Wiring Systems and Enclosures The final choice of a wiring system must rest with those designing the installation and those ordering the work, but whatever system is employed, good workmanship and the use of proper materials is essential for compliance with the Regulations IEE Regulation The necessary skills can be acquired by an electrical trainee who has the corrected attitude and dedication to the craft.

PVC Insulated and Sheathed Cable Installations PVC insulated and sheathed wiring systems are used extensively for lighting and socket installations in domestic dwellings. Mechanical damage to the cable caused by impact, abrasion, penetration, compression or tension must be minimised during installation Regulation The cables are generally fixed, using plastic clips incorporating a masonry nail, which means the cables can be fixed to wood, plaster or brick with almost equal ease.

Cables should be run horizontally or vertically, not diagonally, down a wall. All links should be removed so that the cable is run straight and neatly between clips fixed at equal distances providing adequate support for the cable so that it does not become damaged by its own weight, as shown in Table 4. Where cables are bent, the radius of the bend should not cause the conductors to be damaged.

All joints must be accessible for inspection and maintenance when the installation is completed. Where PVC insulated and sheathed cables are concealed in walls, floors or partitions, they must be provided with a box incorporating an earth terminal at each outlet position. Where holes are drilled in floor joists to accommodate cable runs, they must meet the requirements shown in Fig. Maximum diameter of hole should be 0. Holes on centre line in a zone between 0. Maximum depth of notch should be 0. Notches on top in a zone between 0. Holes in the same joist should be at least 3 diameters apart.

The conduit, in effect, replaces the PVC outer sheath of a cable, providing mechanical protection for the insulated conductors. A conduit installation can be re-wired easily or altered at any time, and this flexibility, coupled with mechanical protection, makes conduit installations popular for commercial and industrial applications. There are three types of conduit used in electrical installation work: steel, PVC and flexible. Steel Conduit Steel conduit offers the conductors within a great deal of protection from mechanical damage.

Steel conduit installations therefore, find an application in industrial environments. The conduit size and range of fittings are the same as those available for metal conduit. PVC conduit is most often joined by placing the end of the conduit into the appropriate fitting and fixing with a PVC solvent adhesive.

PVC conduit can be bent by hand using a bending spring of the same diameter as the inside of the conduit. Where luminaires are suspended from PVC conduit boxes, precautions must be taken to ensure that the lamp does not raise the box temperature or that the mass of the luminaire supported by each box does not exceed the maximum recommended by the manufacturer IEE Regulation PVC conduit also expands much more than metal conduit and so long runs require an expansion coupling to allow for conduit movement and help to prevent distortion during temperature changes.

All conduit installations must be erected first before any wiring is installed IEE Regulation A limit must be placed on the number of bends between boxes in a conduit run and the number of cables which may be drawn into a conduit to prevent the cables being strained during wiring. Appendix 5 of the On Site Guide gives a guide to the cable capacities of conduits and trunking. Flexible Conduit Flexible conduit is made of interlinked metal spirals often covered with a PVC sleeving.

The tubing must not be relied upon to provide a continuous earth path and, consequently, a separate CPC must be run either inside or outside the flexible tube Regulation Trunking Installations A trunking is an enclosure provided for the protection of cables which is normally square or rectangular in cross-section, having one removable side.

Trunking may be thought of as a more accessible conduit system and for industrial and commercial installations it is replacing the larger conduit size. A trunking system can have great flexibility when used in conjunction with conduit; the trunking forms the background or framework for the installation, with conduits running from the trunking to the point controlling the current using apparatus. Most trunking is available in either steel or plastic. Metallic Trunking Metallic trunking is formed from mild steel sheet, coated with grey or silver enamel paint for internal use or a hot-dipped galvanised coating where damp conditions might be encountered.

Alternatively, bends may be fabricated in lengths of trunking, as shown in Fig. This may be necessary or more convenient if a bend or set is nonstandard, but it does take more time to fabricate bends than merely to bolt on standard accessories. The most vanised but PVC used extensively sheet-steel channel with multiple common finish is hot-dipped galcoated tray is also available. Cable tray should be adequately supported during installation by brackets which are appropriate for the particular installation.

The tray should be bolted to the brackets with round-headed bolts and nuts, with the round head inside the tray so that cables drawn along the tray are not damaged. The tray is supplied in standard widths from 50 mm to mm and a wide range of bends, tees and reducers are available. The tray can also be bent using a cable tray bending machine to create bends such as that shown at A in Fig.

The cable sheath provides sufficient mechanical protection for all but the most severe situations, where it may be necessary to fit a steel sheath or conduit over the cable to give extra protection, particularly near floor level in some industrial situations. The cable may be laid directly in the ground, in ducts, on cable tray or clipped directly to a structure.

It is not affected by water, oil or the cutting fluids used in engineering and can withstand very high temperatures or even fire. The cable diameter is small in relation to its current carrying capacity and it should last indefinitely if correctly installed because it is made from inorganic materials. These characteristics make the cable ideal for emergency circuits, boiler-houses, furnaces, petrol stations and chemical plant installations.

Special Installations All electrical installations and installed equipment must be safe to use and free from the dangers of electric shock, but some installations require special consideration because of the inherent dangers of the installed conditions. In this section we will consider some of the installations which require special consideration. Bathroom Installations In rooms containing a fixed bath tub or shower basin, additional regulations are specified. This is to reduce the risk of electric shock to people in circumstances where body resistance is lowered because of contact with water.

Therefore, the metalwork of water and gas installations cannot be relied upon to be continuous throughout. The IEE Regulations describe the need to consider additional or supplementary bonding in situations where there is a high risk of electric shock for example, in kitchens and bathrooms. In rooms containing a fixed bath or shower, supplementary bonding conductors must be installed to reduce to a minimum the risk of an electric shock Regulation Bonding conductors in domestic premises will normally be of 4 mm2 copper with PVC insulation to comply with Regulations to 03 and must be connected between all exposed metalwork for example, between metal baths, bath and sink taps, shower fittings, metal waste pipes and radiators, as shown in Fig.

The bonding connection must be made to a cleaned pipe, using a suitable bonding clip. However, construction sites are dangerous places and the temporary electrical supply which is installed to assist the construction process must comply with all of the relevant wiring regulations for permanent installations Regulation All equipment must be of a robust construction in order to fulfil the on-site electrical requirements while being exposed to rough handling, vehicular nudging, the wind, rain and sun.

This arrangement limits the voltage to earth to 55 V, which is recognised as safe in most locations. A V distribution unit is shown in Fig. Edison screw lamps are used for V lighting supplies so that they are not interchangeable with V site office lamps.

There are occasions when even a V supply from a centre-tapped transformer is too high, for example, supplies to inspection lamps for use inside damp or confined places. In these circumstances a safety extra-low voltage SELV supply would be required. Industrial plugs have a keyway which prevents a tool from one voltage being connected to the socket outlet of a different voltage.

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They are also colour coded for easy identification as follows: V — red V — blue V — yellow 50 V — white 25 V — violet Agricultural and Horticultural Installations Especially adverse installation conditions are to be encountered on farms and in commercial greenhouses because of the presence of livestock, vermin, dampness, corrosive substances and mechanical damage.

In situations accessible to livestock the electrical equipment should be of a type which is appropriate for the external influences likely to occur and should have protection against solid objects and water splashing from any direction Regulation Horses and cattle have a very low body resistance, which makes them susceptible to an electric shock at voltages lower than 25 V rms. In buildings intended for livestock, all fixed wiring systems must be inaccessible to the livestock and cables liable to be attacked by vermin must be suitably protected. All exposed metalwork must be provided with supplementary equipotential bonding in areas where livestock is kept Regulation In many situations, waterproof socket outlets to BS must be installed.

The operating current must not exceed 30 mA and have a maximum operating time of 40 ms with a residual current of mA Regulation Cables buried on agricultural or horticultural land should be buried at a depth not less than mm, or mm where the ground may be cultivated and the cable must have an armour sheath and be further protected by cable tiles. Overhead cables must be installed so that they are clear of farm machinery or placed at a minimum height of 5. Flammable and Explosive Installations Most flammable liquids only form an explosive mixture between certain concentration limits. Above and below this level of concentration the mix will not explode.

The lowest temperature at which sufficient vapour is given off from a flammable substance to form an explosive gas-air mixture is called the flash-point.


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  5. An area in which an explosive gas-air mixture is present is called a hazardous area, as defined by BS , and any electrical apparatus or equipment within a hazardous area must be classified as flameproof. Flameproof equipment is manufactured to a robust standard of construction.

    All access and connection points have wide machined flanges which damp the flame in its passage across the flange. Flanged surfaces are firmly bolted together with many recessed bolts, as shown in Fig. All certified flameproof enclosures will be marked Ex, indicating that they are suitable for potentially explosive situations, or Eex, where equipment is certified to the harmonised European Standard.

    All the equipment used in a flameproof installation must carry the appropriate markings, as shown in Fig. Flammable and explosive installations are to be found in the petroleum and chemical industries, which are classified as group 11 industries. Mining is classified as group 1 and receives special consideration from the Mining Regulations because of the extreme hazards of working underground.

    The installation method chosen will depend upon the contract specification, the fabric of the building and the type of installation — domestic, commercial or industrial. It is important that the wiring systems and fixing methods are appropriate for the particular type of installation and compatible with the structural materials used in the building construction.

    The electrical installation must be compatible with the installed conditions, must not damage the fabric of the building or weaken load-bearing girders or joists. The clips are supplied in various sizes to hold the cable firmly and the fixing nail is a hardened masonry nail.

    The use of a masonry nail means that fixings to wood, plaster, brick or stone can be made with equal ease. Wood screws may be screwed directly into wood but when fixing to brick, stone, plaster or concrete it is necessary to drill a hole in the masonry material, which is then plugged with a material to which the screw can be secured. Plastic Plugs A plastic plug is made of a hollow plastic tube split up to half its length to allow for expansion. Each size of plastic plug is colour coded to match a wood screw size.

    A hole is drilled into the masonry, using a masonry drill of the same diameter and to the same length as the plastic plug see Fig. The plastic plug is inserted into the hole and tapped home until it is level with the surface of the masonry. Finally the fixing screw is driven into the plastic plug until it becomes tight and the fixture is secure. Tightening the bolt draws up an expanding bolt inside the split iron shell, forcing the iron to expand and grip the masonry. Rawlbolts are for heavy duty masonry fixings see Fig. The iron shell is inserted with the spring wire clip end first so that the ferrule is at the outer surface.

    The bolt is passed through the fixture, located in the expanding nut and tightened until the fixing becomes secure. For the most robust fixing to masonry material an expansion bolt, such as that made by Rawlbolt, should be used. Spring Toggle Bolts A spring toggle bolt provides one method of fixing to hollow partition walls which are usually faced with plasterboard and a plaster skimming. Plasterboard and plaster wall or ceiling surfaces are not strong enough to support a load fixed directly into the plasterboard, but the spring toggle spreads the load over a larger area, making the fixing suitable for light loads see Fig.

    A hole is drilled through the plasterboard and into the cavity.

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    The toggle wings are compressed and passed through the hole in the plasterboard and into the cavity where they spring apart and rest on the cavity side of the plasterboard. The bolt is tightened until the fixing becomes firm. Girder Fixings In many commercial and industrial buildings it is necessary to fix trunking, conduit and tray to the structural fabric of the building.

    However, spring clips or compression brackets are available which attach to the girders and hold the electrical systems securely. The process of inspection is a visual thing. The process of testing implies the use of instruments to obtain readings. The tests required by the Regulations BS Requirements for Electrical Installations, must be carried out in the order given below so that safety systems are tested first. If any test indicates a failure to comply, then that test and all preceding tests must be repeated after the fault has been rectified.

    Continuity of Protective Conductors CPCs The objective of the test is to ensure that every circuit protective conductor is correctly connected and has a very low resistance. The resistance of the long test lead is subtracted from the test readings to give the resistance value of the CPC. The test is made at the consumer unit with the supply disconnected using an insulation resistance meter which supplies a voltage of V.

    Pilot indicator lamps, discharge lighting and electronic equipment must be temporarily disconnected before this test begins to avoid false readings and possible damage to equipment as a result of the test voltage. Relevant criteria tells us that a satisfactory test result would be a minimum resistance value of 0. Polarity The object of the test is to ensure that all fuses, MCBs and switches are connected in the phase conductor only and that all socket outlets are correctly wired.

    Relevant criteria tell us that a satisfactory test result would be a very low resistance value, approaching zero ohms for each test. When all the tests are completed and proved satisfactory, the supply may be switched on. Functional testing means that devices are operated to confirm that they are working properly and are correctly adjusted.

    Electrical Test Instruments Electrical installation testing in accordance with the relevant Regulations demands that we use specialist test instruments. It is unacceptable for a professional electrician to carry out electrical testing using instruments bought at the local DIY superstore.