Electrical Installation

Installation materials And wiring methods

This has been designed to assist your core learning programme, should you require more information, consult your lecturing staff.

Containment To provide cables with a route from one part of a building to a point where the supply current can be used, will require cable protection, this is usually provided by either trunking or conduit or cable tray, ladder rack, ducting or other means of containment. Cables must be protected from high and low temperatures, mechanical damage, chemicals, the weather, chemical reaction, animals and many other things which may be found within the building structure.

Directed questions – Can you list three types of containment systems ……………………………………………………………….. Can you name the fixing method and the individual parts shown above ………………………………………………………………………

Trunking This is used to provide a service route for circuit cables; it is used to apply mechanical protection. The most common cable used with trunking is single core cables to BS6004, cable manufacturer number 6491x. There are many types of trunking, each with many types of finish, each type for one particular installation method, and these methods can be found in appendix four of BS7671. This wiring system is used where many circuits are to be installed, usually from three phase distribution boards to areas, the circuits are then individually protected locally. In most modern buildings, there can be installed at least three categories of circuits, 400V/230V , ELV circuits, data, communication, signal circuits etc, the third category being fire alarm and emergency lighting. Self study- List a type of trunking that can carry all three categories of circuits ………………………………………………………………………….. Which type of fixing screw should be used for trunking ………………………………………………………………………….. Which device is used to provide earth continuity between trunking joints ……………………………………………………………………………. Which installation method found in BS7671 is listed for surface trunking ……………………………………………………………………………..

Trunking finishes and types Hot dipped galvanised

Grey enamel on zinc coating Silver enamel on zinc coating Stainless steel Lighting Trunking Cable trunking Three-Compartment trunking Bus-bar Trunking

Standard Sizes of Trunking

50mm x 50mm 150mm x 75mm

75mm x 50mm 150mm x 100mm

75mm x 75mm 150mm x 150mm

100mm x 50mm 200mm x 100mm

100mm x 75mm 225mm x 150mm

100mm x 50mm 250mm x 150mm

100mm x 100mm 300mm x 250mm

Trunking is generally supplied in 3 metre lengths. Lighting trunking is often supplied in 5 metre lengths. Other lengths are available on request. Self study- Give one typical installation where each of the trunking finishes is found …………………………………………………………………………….. ……………………………………………………………………………

Lighting trunking Steel trunking may be used to install luminaires. This type has quick fit drive-in couplings, which allow for fast, easy installation of long runs. The trunking is installed with the opening downwards .

Lighting trunking quick joint assemply

Self study

Which type of luminaire is normally installed to lighting trunking ……………………………………………………………………………….. Give two advantages of lighting trunking ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………….

cable trunking Standard cable trunking is similar in design to lighting trunking. The lid in this case is held in place with turnbuckles. A quarter turn of a large flat screwdriver will either fasten or loosen the turnbuckle. For final circuit connections, conduit is normally installed to the local isolator before connection to equipment; this can be carried out by flexible conduit where necessary.

Typical cable trunking Lid and turnbuckle According to current installation standards, how much room is available for cables within trunking ………………………………………………………………………………..

Joining sections Where long runs of trunking are installed, several lengths may be joined together using joining pieces. In most cases, 6mm screws or nuts and bolts are used to fasten sections together, copper earthing tags should be used to ensure electrical continuity.

Self study Which other method of joining trunking may be used ……………………………………………………………………

Fittings There are many off the shelf, standard trunking fittings available from most electrical wholesalers. Trunking can also use reducers where sizes are decreased or enlarged to suit the number of cables being installed.

Flat right angle bend

Tee section

End cap

45 degree set

reducer

Cable retainer

Three compartment trunking

Self study Where data cables overlap 230V cables within three compartment trunkng, which accessory is used to segregate cables. ……………………………………………………………………………………. Where trunking passes through concrete floors, name the fire prevention device installed in trunking ………………………………………………………………………………………

Use of trunking Steel trunking systems are used in commercial and industrial premises. Lighting trunking is generally used to supply and support fluorescent fittings, which illuminate large floor areas. Cable trunking is installed at a suitable height around the walls of the building. Conduit drops are then used to supply outlet points. Multi-compartment trunking is used where different electrical services are required in close proximity to each other. It is ideal in large offices and classrooms. Here it may be used to accommodate cables for supplying equipment at 230 Volts, plus data cables for computers, printers etc. These supplies must be segregated from each other.

Types of Support

Trunking should be secured by round-headed screws or bolts. This prevents damage to cables during installations. In industrial installations, trunking may be run overhead, supported at intervals by the lower members of the roof trusses. It may be suspended from or fastened directly to right angle brackets. It may also be fixed directly to a wall surface. a number of fixings, which may be used to support trunking are shown

The trunking shown below is supported by suspension brackets. The threaded rod known as stud also allows for final height adjustment.

Spacing of Supports

The spacing of trunking supports is not a simple topic as there are so many variables such as: - size of trunking, size and number of cables to be installed, type and strength of support available. However the following table lists the maximum distances between supports for steel trunking.

Maximum Support Spacing for Steel Trunking

Trunking Size Horizontal Vertical

50 x 50 1.75 2.0

75 x 50 3.0 3.0

Larger Sizes 3.0 3.0

Self study A trunking is to carry twenty circuits, each circuit is single phase with single core cables, determine the size of trunking to meet BS7671 standards, where the cables will be three lighting circuits, four ring final circuits, four radial power circuits, one cooker circuit of 8KW Two shower circuits of 8.7 KW , two outside lighting circuits of 2.2 kw Each and four sub circuits of 6mm cables, show working out. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. ………………………………………………………………………………………….

Fabrication and Installation of Tees and Bends

Tees and bends may be fabricated where required in lengths of trunking. This may be necessary or simply more convenient, particularly if the required bend or set is non-standard. It takes more time to fabricate tees or bends than to bolt on manufactured accessories.

Where overlap joints are made, use a file to cut trunking edges, bend using pliers to form overlap, this will provide a quality finish, and allow for pop rivet or nut and bolt sturdy fixing.

Over lapping right angle bend

External bend

Forming a flat bend

Earthing of Steel Trunking

A trunking installation must be earthed. Earth continuity is ensured by the proper tightening of all bolts used throughout the system. Some manufactures recommend that earth continuity be completed by fixing a copper or aluminium strap across all joints. It is more important that all the bolts involved in the system are tightened. It is not unusual to find that copper or aluminium straps are used, but are left loose, resulting in poor earth continuity

Self study Explain why burrs must be removed from formed bends and sets ………………………………………………………………………………….. ………………………………………………………………………………….. Which test is used to prove earth continuity of trunking systems ……………………………………………………………………………………. Indicate a suitable continuity test value ……………………………………………………………………………………….

Busbar trunking Where incoming supplies are installed, these are designed to meet the total demand of the building. This supply is then used to supply sub main cables to designated areas And then each area may supply separate three phase distribution to individual circuits. It is good practice to install separate isolators to each area, this allows for maintenance and testing to be regularly carried out.

Self study Show, by use of a flow chart, how supplies to a single phase C.U. are established from an incoming three phase busbar.

Cable tray A wiring system that is used in commercial and industrial installations, it is used because it can be adapted easily and cables can be installed along its length allowing for future expansion. As it is accessible, the heat from cables is not usually a factor because the air around the conductors will cool the cables naturally. There are many materials used, each type has a finish to cope with the external influences it may be subject to. It is generally supported throughout its length by installing support brackets at regular intervals, these brackets are usually installed using studding and nuts which allows for correct height.

Self study List two cable fixing devices used on cable tray ………………………………………………………………………….. List three finishes and types of installation …………………………………………………………………………… …………………………………………………………………………… ……………………………………………………………………………..

Joints and reducers

Where joints are made or where junctions are formed using cable tray, as with trunking it should be overlapped and have earth continuity links fitted.

Cable tray Finishes:

Hot Dip galvanised, Powder Coated, Red oxide, Enamel Painted.

Where would red oxide finish cable tray be installed

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Basket

A cable tray used for quick installation of cables above ceiling level. This type of tray is usually fixed using clip on adjustable hangers And cables are fixed using tie-wraps.

Nylon tie wrap Tie wraps come in all diameters and lengths, these are easily installed and removal is just as quick, must be used correctly by inserting the grip end, these are also used inside distribution boards for neat, tidy cable installation.

Velcro tie wraps Velcro tie wraps are use for fixing cat 5 and data cables to basket. This is to avoid loss of signal due to insulation failure which can occur if ordinary plastic tie wraps are used and over tightened.

Fibre glass tray In some installations, it may be necessary to install fibre glass tray work, this is mainly because of the type of installation, oil rigs and petrochemical installations are the main types.

Although light in weight, the strength to weight ratio surpasses that of equivalent steel products. Fibreglass tray weighs 1/3 that of steel trays and is pound for pound stronger. This makes the tray easy to install, reduces the possibility of lifting accidents, and lowers transportation costs. Fibreglass Cable Tray is available in both polyester and vinylester resin systems. They are manufactured to meet ASTM E-84, Class 1 Flame Rating and self-extinguishing requirements of ASTM D-635. It will not rust, nor does it ever require painting. FRP cable tray is available in two colours: gray (polyester resin) and beige (vinylester resin), with custom colours available upon request. A surface veil is applied during the pultrusion process to ensure a resin-rich surface for superior corrosion resistance, as well as an ultraviolet exposure barrier.

From paper mills to refineries to laboratories, sound electrical design requires an adaptable FRP cable support system that is reliable. Above all, durability and resistance to corrosion lead to lower overall costs during the life of the installation.

Steel Conduit System

Types and Sizes of Steel Conduit Steel conduits are manufactured to specifications defined by the British Standards Institute BS EN 61386-1:2008

There are many types of conduit, from black enamel, galvanised, stainless steel and sherazised. Note: The galvanized finish on conduit is to prevent the steel from corroding

in normal use.

Also manufactured is a solid drawn seamless conduit which is more expensive and only used for special gas tight, explosion proof or flame proof installations.

Conduit is normally supplied in 3 metre lengths and typical conduit external diameters are 16, 20, 25 and 32mm.

Black enamel

This type of conduit is used as mechanical protection for single core cables or for twin and earth cables, this conduit is used to prevent damage to cables which are not situated either in safe zones or where they are installed horizontally or diagonally, in these circumstances to meet Requirements of BS7671 and buiding reguations, conduit must be used for protection from

drill bits and other penetrating tools from causing short circuits or giving rise to possible electric shock.

It can be installed internally, where single core cables are used as the wiring system.

Galvanised

This is used for external work, or where there may be damp or moist atmospheres.

Where this type of conduit is used, threads will need to be painted to prevent the conduit becoming corroded, this is essential,especially at coupled joints, corrosion will cause high resistive joints which may lead to a breakdown of earth continuity of the conduit, causing a risk of shock.

Stainless steel A conduit used where the manufacture of food preparation is carried out, has a good appearance and adds to the aesthetic quality when required. Will be installed in installations such as the pharmaceutical industry and where hygiene is considered paramount.

Sheradised conduit A type of conduit used where exposure to chemical or salt water is present, such as lighthouses and marinas. Sheradising is a form of galvanising steel that prevents corrosion and this type of conduit should be used where chemical reaction may occur,

Forming conduit Conduit can be bent, set and formed into double sets using a bending machine.

This type of bending machine is known as a vice and bender, conduit is cut, bent and threaded on site, the formers allow for different size conduits to be bent.

Forming steel conduit

To bend to outside measurements Mark off the tube to the required distance. For example, if the measurement from the end of the tube to the outside of the bend is to be 600mm, mark off 600mm - Figure 10. Insert the measured part in the machine so that it rests against stop E (Figure11), and push the tube right into the former. Place a square against the mark on the tube and slide the tube until the square touches the outside edge of the former - at X in Figure 11. The tube is now in the correct position for bending.

figure 11

To bend to inside measurements If the measurement is from the end of the tube to the inside of the bend, mark off 600mm and place the tube in the machine as above - but slide the tube until the square (coinciding with the mark ) touches the bottom of the groove in the former - at K in Figure 11. NOTE: The principle explained above maybe applied to make a bend at a given distance from another bend, depending on whether the measurement is from outside to outside or outside to inside of bend. Offsets After making the first bend (usually to 45°), place the tube in the machine as shown in Figure 12, resting it against the stop E and bedding it into the groove of the former. Suppose the offset required is to measure 100mm (Figure13). Place a straight-edge (or piece of straight material) against the outside edge of the former and parallel to the tube at Y, and adjust the tube in the machine until you obtain the required measurement.

NOTE: The set will increase as you push the tube to the right, and decrease as you push it to the left in Figure 12. When you have obtained the correct measurement, bend in the usual manner until the tube M is parallel with Z. If you want to make a number of similar offsets, make the first bend in all the tubes. Then place one tube in the machine to the correct measurement and mark it at the spot where it touches the stop.

Bending steel conduit 1. Pass the conduit through the gap between the tube stop and the former, and bed it into the former groove (Figure 3). 2. Check that the free end of the conduit will not touch the ground before the bend is complete. The maximum lengths are 900 mm for the EL25 and 1100mm for the EL32. If there is insufficient clearance, go to step 4. 3. Withdraw the bending lever retaining pin and pull the bending lever down until the bend is complete (Figure 4).

4. If the free end is too long to enable you to complete the bend, remove the conduit. Release the bending lever, and swing it and the stop bar downwards. Load the conduit as in Step 1 and pull the bending lever upwards until the bend is complete. NOTE: When you use the machine in this way, you should steady it by placing your foot on the front leg cross member (Figure 5).

6. DOUBLE SET

• Align first mark with front of former • Pull first bend. • Align with second mark. • Rotate conduit through 180 Pull second bend.

Former Guide Former

Guide Former Guide Former Guide Former Guide Former Former Guide Former Guide Former Former

Former Guide Former Guide Former Guide Former Guide Former Guide Former Guide Former Guide Former Guide Former Guide Former Guide

Saddle set • Align centre mark with front of former • Pull first bend. • Align with second mark. • Pull second bend .o Rotate conduit through 180mer

Pull third bend Adjust bends until square

Steel conduit ,cutting and threading Mark the conduit to the desired length, use a hacksaw with 32 teeth per inch, place in the vice on the bending machine and lock tightly, the correct cutting angle is achieved with this action, do not use a bench vice. Using the whole length of the blade, cut away from the body until the conduit is cut straight and accurate. Using the stocks and dies, push and turn until the conduit is gripped by the dies, turn the dies twice so that two threads are cut into the conduit. Turn the dies anti-clockwise and remove from the conduit, bang the dies slightly to remove swarf from the first thread cuts, spread tallow or cutting lubricant onto the conduit , then keep threading, regularly turning backwards to remove swarf, a half coupler thread is usually three threads past the end of the dies. Once threading is completed, use a reamer to clean the inside of the conduit, this will remove burrs, use a rag or towel to clean the conduit.

Stocks, dies and guides

Former Former

Former reamer

Conduit boxes There are many types of boxes used for connecting threaded conduit, light fittings, switch and socket boxes, to name but a few. In the pictures shown below, name the following conduit boxes and their use.

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Conduit threads and fittings There are generally two types of conduit threads, the most common being a half socket thread or half a coupler length, this is used to join lengths or sections together.

the second type of thread is known as a runner, it is one whole coupler plus a lock ring, this is used to join sections where there is not the room to turn the conduit to an acceptable tightness, remember, conduit should be fitted so that continuity is maintained, loose connections will not achieve this.

Female bush male bush

Female bushes are used to protect cables when they are installed into the conduit, the sharp edge may damage cable insulation. Male bushes are used to join couplers and boxes to conduit, these must be tightened with a bush key.

Milled edge lockring ET Hook

Milled edge lockrings are used to join conduit using nipple threads to boxes or used to keep couplers in place when using runner threads. ET hooks are used to hang jack chain for suspended light fittings, the flex is often passed through the outlet and into the fitting.

Nipple thread box lid

Nipple threads are used to join conduit to fixed conduit boxes, they can be made by threading conduit and cutting to the desired length, box lids are used to stop the ingress of solid material into the conduit system, helping to protect the cables.

4mm pan head box lid screws gasket

Pan head screws are used to fix extension rings and box lids to conduit boxes, they come in various lengths, gaskets are used to stop the ingress of moisture and water from entering the conduit system.

crampet extension ring

Crampets are used to fix conduit to masonry walls, usually used to fix conduit into a chased wall recess, extension rings are used where there is a fitting fitted into a conduit box and cables require more space as they are too bunched and may overheat, the ring allows for adequate space behind a fitting.

Tallow compression gland

Tallow is used as a lubricant when cutting conduit threads, there are many types made which are oil based to aid good thread cuts, these include trefolex, compression glands are used to install flex from the conduit system to a piece of installed equipment, the flex is usually connected inside the conduit box to the main wiring by means of a connector block or other terminal connection.

Self study What is the main purpose of installing conduit boxes ……………………………………………………………………………….. How is moisture removed from an enclosed conduit system ………………………………………………………………………………… Why would jack chain be fitted to conduit boxes …………………………………………………………………………………. What is an adaptable box …………………………………………………………………………………. BS7671 states that where other services are installed in a building, electrical conduit should be identified by which colour ……………………………………………………………………………………

Types of conduit saddle Saddles are used to fix conduit to surfaces, the are adaptable to be able to level the conduit system, the saddles are fixed in position by screw and rawlplug, the screw type should be countersunk as this allows the saddle to be solid against most wood and masonry. Spacer bar saddle distance saddle

Spacer bar saddles are used to fix conduit to either masonry or wood surfaces, once fixed they can be easily moved to adjust the conduit so that is level, distance saddles allow conduit to fit directly into surface mounted switch or socket boxes without the need to slightly double set the conduit for entry into the box. Hospital saddle

Hospital saddles are installed so that cleaning can easily be carried out behind he conduit, hence the name “hospital”

Flexible conduit Where conduit is fitted between the fixed conduit installation and a piece of machinery which either vibrates or may cause damage to the fixed conduit flexible conduit is used, one example of this would be the final conduit to a motor, special couplers and connections are used, a circuit protective conductor must be installed in this type of conduit as earth continuity will not be continuous as there is usually an insulated break.