Intruder alarm wiring systems
Regulations cover the segregation of cables of different categories and the susceptibility of electromagnetic interference.
Good practice is required to ensure the neatness of the finished system and mechanical protection of vulnerable wiring. This chapter provides knowledge of the techniques involved in installation practices.
This chapter familiarizes the student with the constructional features of the wiring conductors that are employed in the security industry, and ensures that their applications are understood. The types of terminations and connection methods that are generally encountered are also discussed.
Cables will be found alongside flexible cords in a number of different guises. These can be PVC (polyvinyl chloride) insulated or sheathed and may also be fire resistant. The terminations and joints will be soldered or mechanically formed, and so will have differing mechanical and electrical properties.
In addition to citing the standards governing the joining of wiring, some study must also be made of how these standards relate to the segregation and support of wiring. The installation of wiring systems must therefore cover the methods of fixing to various surfaces and the reasons for any particular selection, including the use of conduit and trunking. Allied to these needs is a requirement to be aware of the methods that can be employed to fix alarm equipment to the various surfaces that will be encountered, and an important area in this regard is the mounting of external audible intruder alarm signalling devices.
Also within this chapter we investigate the use, care and maintenance of ladders and stepladders.
7.1 Survey of modern wiring methods
We must first consider how the chief methods of electrical wiring systems are applied throughout the electrical industry before we can look directly at the ways the wiring can be employed in the intruder alarm sector.
A general survey of the chief methods is appropriate to aid the installation engineer in helping him or her determine the particular wiring technique most suited to any given application. Reliability and ease of installation both come into the equation, together with the cost. In the intruder alarm areas we are accustomed to particular cables being utilized, but there are many different ways that these can be protected. BS 4737: Part 1: 1986, which is applicable to all internal complete systems, states that the system should comply with the British Standard under the environmental conditions to which it is liable to be subjected at the protected premises. These conditions include potential causes of mechanical damage as well as weather and heat. Problems can also occur as a result of dampness, corrosion, oil and electrical interference or because of an adverse industrial atmosphere. Indeed, this standard imposes stringent requirements on the installer, and it becomes essential that room data sheets include records pertaining to the environment. Persons commissioned to install intruder alarm wiring may not of necessity be qualified electricians but nevertheless the standard of work must be to the same high level. With this in mind we shall consider how wiring is installed and protected in the electrical engineering sector.
Steel conduit systems
With this method steel tubes are fixed to the walls and building structure, and cables are drawn into them at a later stage. The cables are usually PVC insulated and sheathed or non-sheathed, and, for mains wiring techniques, may be single core. Although the tubes can be fixed to the surface of the building, the full advantage of this method is realized in a building which is in the course of erection as the conduit may then be fixed to unplastered walls or chased into brickwork before being encased in plaster. The cables should not be drawn into the conduit until the plaster has had some time to dry, to prevent the ingress of any moisture into the tubes from the wet plaster.
Types and grades
Conduit is supplied in standard lengths of 3.75 m in diameters of 20 or 25 mm conforming to BS 4568. Steel conduit is black enamelled or galvanized, and threaded at both ends. For aggressive environments high-grade 316 stainless steel conduit is available; this type of conduit is able to cope with chloride-laden conditions, and is therefore ideal for applications in the food, brewing, dairy, pharmaceutical and chemical industries. As stainless-steel conduit also has an aesthetically pleasing finish it can be utilized for purely architectural reasons.
Non-metallic conduit systems
Although recognizing that steel conduit provides excellent protection of all cables to mechanical damage and also gives earth continuity, there are certain disadvantages to its use. These largely relate to condensation, rusting and corrosion of the material. In the long term this can lead to decreased protection and loss of efficient electrical continuity. It is therefore always worth considering non-metallic conduits, which are available in either rigid or non-rigid forms. They are made of PVC capable of providing high impact resistance, and are usually available in 4 m lengths with the same diameters as steel conduit (20 or 25 mm).
PVC-based conduits have the following advantages:
• High resistance to corrosion by water, acids, alkalis and oxidizing agents. These materials are also unaffected by the chemical components in concrete and plaster.
• Do not deteriorate significantly with age or external exposure.
• Not susceptible to water condensation.
• Excellent electrical properties, with an electrical breakdown voltage of the order of 12–20 kV/mm.
Rigid conduit
The most commonly used type of rigid conduit is ‘unplasticized’ PVC conforming to BS 4607. It has plain bored ends and two wall thicknesses, either heavy (standard) or light gauge, and is generally coloured black or white.
In practice, heavy gauge conduit is installed on surface installations where mechanical damage is a distinct risk. The normal method of joining and applying fittings is by the use of push fitting. The push fit conduit entry ensures a tight, reliable fit, and when used in conjunction with PVC adhesive a strong permanent joint can be attained. For protection in damp conditions, solid rubber gaskets can be employed.
Flexible plastic conduit
This is available in long coiled lengths usually of 25 m, and is used for sunk or concealed wiring in cases where its appearance is not of importance. It has great flexibility and enables awkward bends to be negotiated, and can be threaded through holes easily. The conduit can be applied over irregularities in wall surfaces without difficulty, and can withstand the stresses imposed upon it when floors are awaiting screeds. Flexible conduits are normally of 20 mm diameter.
Trunking
We have said that the erection of conduit should be done before running in the cables; however, there is an alternative form of cable protection available which permits the cables to be installed even prior to the protection being fitted. This is PVC trunking, and it is widely used by the intruder alarm engineer. It can even be applied at the very last stage of an installation or to an existing application. This is a form of channel manufactured from high-impact PVC and featuring a locking or double-locking lid that is pushed into position and held within its longitudinal channel ridges. Trunking is normally supplied in a white finish, has a high aesthetic appearance, and is ideal for most types of electrical installations from security to fire and lighting and power systems. It is manufactured to comply with BS 4678 and can either be held in position by fixing its back channel section in place with plugs and screws or using a self-adhesive foam strip, if the surface to which it is to be applied is free from dust and grease. Outlet boxes to complete the installation are also available to ensure an adequate level of mechanical protection as required by the IEE Wiring Regulations. Trunking is generally available in standard lengths of 3 m, and is easily cut to size. There is also a range of sizes available to suit the cables that are to be accommodated, the following being the most commonly encountered:
| Width (mm): | Depth (mm): |
| 16 | 12.5 |
| 16 | 16 |
| 20 | 10 |
| 25 | 12.5 |
| 25 | 16 |
| 38 | 16 |
| 38 | 25 |
| 38 | 38 |
As with conduit, a range of accessories can be purchased to make up the installation. These range from couplings that are used to join the lengths of trunking to box adaptors, ‘T’ pieces, flat angles and internal and external angles to negotiate bends and corners or to make up branches. Blank ends are used to terminate runs and to enclose the end of the trunking for both strength and aesthetic purposes.
A range of PVC mini-trunking can also be sourced, and which is supplied in a dispenser box as a flat coil some 15 m in length. It is easily cut to the desired length, reducing waste and the necessity for excess joints and couplers. It is fixed to the required surface in a flat form, and the sides may then be folded up and the lip clipped into place. Once again, accessories are available to extend its use, including outlet boxes.
Although the intruder alarm engineer will rarely use galvanized trunking and fittings, they are occasionally encountered in industrial environments, where they are used to protect mains supplies. These are manufactured from precoated galvanized steel with the lid fastened by integral fixing bars that engage the trunking body when the captive lid screws are rotated through 90°. Another product is the standard flange tray, which is designed to carry heavy cable installations. Alarm cables must never be run in close proximity to either galvanized trunking or flange trays when carrying mains supplies.
There is one further form of support that can be used for alarm or signal cabling, known as dado or bench-type trunking. This is effectively installed as skirting and is an effective means of running cables at a low or bench height. This type of protection tends to be manufactured either in PVC or sheet steel with a white epoxy paint finish. Again, accessories to complement the trunking are available.
Aluminium tubing
A further form of cable protection that is at times used for alarm wiring is that of tubing using aluminium tube of 12.5 mm diameter. This method is in fact a long-established means of protecting taut wiring used as a detection device for openings such as windows. The tubing can, however, also be found protecting individual cables in some installations where trunking is not practical, such as in external applications where the superior appearance of the tubing and total enclosure of the wiring are wanted. Aluminium tubing does not corrode and therefore has a role to play in harsh environments. It is purchased in 3 m lengths and is easily cut to size. It is joined by clamp couplings that feature screws and bolts that fix the coupling ends over the tubes being joined. Elbows to negotiate bends and changes of direction are also applied by a clamping technique, and saddle clamps are used to fix the tubes to the building structure.
PVC channelling/capping
PVC-sheathed cables running along walls may be buried directly in the plaster but they are better protected by placing metal or PVC channelling over them. This gives a level of resistance to nails being driven into the wall, and in the case of conduit permits the cables to be withdrawn at a later stage if so desired. The channelling we have mentioned is sometimes called capping, and is generally used for the protection of electrical installation cables when surface wired to brick/block work prior to plastering or rendering. Supplied usually in PVC material in a variety of lengths, it is so flexible that it can be carried in reels; it is also shatter-proof, so it will not crack when nailed in position. It takes up the contours of the wall and is easily cut to length using cable cutters or shears. It is manufactured from insulated self-extinguishing material having low smoke, low toxicity and low acid emission properties. Various widths are available to accommodate different volumes of cables. Once the cables have been installed, the capping is simply placed in position over them and nailed into position. It also aids the plastering process in that cables are securely fixed and supported before this process is commenced. Although metal capping is also available, as mentioned, it has been largely superseded by its PVC counterpart.
All-insulated sheathed wiring systems
The principal type of cable that the intruder alarm engineer will be familiar with in so far as the mains supply is concerned is PVC insulated and sheathed cable. It is manufactured as single core (known as ‘singles’), two-core (known as ‘twin’) and two core with an uninsulated protective conductor (known as ‘twin and earth’) surface wiring cable. It is the last type that the alarm installer will be mainly involved with, together with three-core cable or cord that has three insulated cores within the outer sheath. These are used for surface wiring systems or are simply buried beneath the plaster or concrete, although in some instances mechanical protection may be needed. PVC cable will resist attack by most oils, solvents, acids and alkalis. In addition it is unaffected by the action of direct sunlight and is non-flammable, and is hence suitable for a wide range of internal and external applications.
PVC-sheathed cables can be run between floors and ceilings and dropped down through ceilings to spur outlets and such. Holes made for the passage of cables through ceilings can easily be filled with cement or another building material as a precaution against the spread of fire.
In so far as BS 4737 is concerned, there is still a need for the cable to be well protected, be it the mains cable for safety or the alarm cable for security. BS 4737: Part 1: Section 3.2.3 requires that the entire system be protected from all likely damage, including mechanical, electrical and environmental. The interconnecting cables must be adequately supported and their installation conforming to good working practice.
BS 4737 further states that interconnecting wiring must not be run in the same conduit or trunking as mains cables unless they are physically separated. IEE Wiring Regulations do not permit the running of extra low-voltage cables with mains cables unless the insulation resistance of both are equal; however, it is usual practice to not run alarm cables alongside mains cables or even to run them through the same holes in building structures or to feed them through the same hole when entering an alarm control panel or power supply unit. There are special types of trunking available with separate compartments, and these can be employed for neatness and convenience.
BS 4737: Part 4.1: Section 4.5.2 requires that wiring be screened and protected from radio and electrical interference, which further enhances the need to keep the intruder alarm wiring separate from the mains cabling. Although the problems in the industrial and commercial sectors with regard to interference are much greater, this requirement applies to domestic practices also. Alarm wiring must also be kept separate from category 3 (fire alarm) circuits to ensure that they have the necessary resistance to extraneous environmental effects induced by category 1 (mains voltage) circuits.
The specific wiring requirements cited as a minimum standard by BS 4737 is that alarm cables be multistrand four-core insulated and sheathed. These will be classified as hard wired and be essentially of 12 V DC type. Traditionally they may be referred to as communications cable, of very small diameter and using stranded conductor cores. This cable is governed by BS 4737: Part 1: Section 3.30:1986, ‘Specification for PVC insulated cables used for interconnection wiring in intruder alarm systems’, as follows:
• The cable is only for use in internal locations and not for those areas exposed to the weather unless suitable protection is afforded.
• Cables must be segregated and shielded from interference in accordance with Part 4.5.1: Section 4.1 of the British Standard.
• Conductors are to comprise solid annealed copper manufactured to BS 4109 Condition 0 with the strands to be plain or tinned surface coated.
• Solid conductors must have a minimum cross-sectional area of 0.2 mm2 in line with BS 6350: 1988. If under 0.5 mm2 cross-sectional area, the resistance is to be 95 
km for 0.2 mm2 at 20°C and then pro rata to 0.5 mm. Stranded conductors should have a minimum cross-sectional area of 0.22 mm2 to BS 6360: Table 3: 1981: Class 5.
• For cores comprised of conductors, solid or stranded conductors should be a minimum of 7 ×0.2 mm in diameter. Each core must be covered with type 2 or T11 PVC insulation manufactured to BS 6746 with a minimum thickness of 0.15 mm. The insulation must not adhere and it must also allow for easy stripping without causing damage to the conductors. The cores must be capable of withstanding a 1500 V RMS electric strength spark test. A cable is to comprise a number of cores of wires. Cables are to be sheathed with type 6 or T11 PVC manufactured to a BS 6746 with a minimum thickness of 0.4 mm and should include a rip cord to enable easy removal of the sheath without excess cutting that could lead to damage of the conductors or cores.
• The cable should be able to withstand an insulation resistance test of 500 V DC for 1 minute between each conductor and for all remaining conductors in the cable with an insulation resistance of no less than 50 M for 100 minutes at 20 ± 5°C.
• Cables should be wound on to drums with an indication of the name of the manufacturer. The length of the cable should also be designated together with the number of cores, minimum cross-sectional area of the conductors in square millimetres, number and diameter of strands in a stranded conductor (e.g. seven at 0.2 mm), British Standard number and the date.
In practice, the intruder alarm engineer will be sourcing signal cable that will be generally specified as follows:
| Maximum working voltage | 60 V RMS |
| Maximum current | 1 A per core |
| Maximum conductor resistance | 92.4 /km at 20°C |
| Maximum operating temperature | 70°C |
| Conductors | 7/0.2 mm strands of annealed copper wire conforming to BS 6360 |
| Insulation | PVC radial thickness 0.2 mm nominal, confirming to BS 6746 |
| Sheath | PVC nominal wall thickness 0.5 mm |
| Nominal overall diameter | 4 core: 3.5 mm 6 core: 4.1 mm 8 core: 4.5 mm |
| Wire insulation colours | 4 core: red, blue, yellow, black 6 core: red, blue, yellow, black, white, green 8 core: red, blue, yellow, black, white, green, orange, brown |
This cable will be advertised generally as general-purpose four-, six- or eight-core signal cable ideal for use with security alarm systems and other similar applications where low voltages and currents are employed. The cable contains flexible wires each having seven strands of 0.2 mm tinned annealed copper insulated wire.
This cable will of course satisfy the vast majority of wiring functions within the intruder alarm sector covering the detection devices and signalling equipment although connections to remote signalling components employing British Telecom (BT) approved equipment must use approved and type-tested cable.
It is possible to obtain cable to the same specification but with an even greater number of cores, of which 12-core cable is an example, but because of the greater use of multiplex bus wiring and addressablealarm systems we can see a move to conductors with fewer cores to achieve the same end-result. There will also be moves in the future towards high-grade shielded transmission cables.
The BT type-approved cable for connection of remote signalling equipment must conform to the requirements of BT specification CW1308. This cable has 1/0.5 mm tinned annealed copper conductors (single core) and is covered with 0.15 mm PVC insulation and an overall outer PVC sheath. It has a voltage rating of 80 V AC at up to 10 kHz and an insulation resistance of 50 M at 20°C. The identification system is different for BT type-approved cable, as it uses a pair method of coding in that the base colour of a core of a pair is the band colour of the other core, thus white/blue and blue/white through to orange and green for a three pair (six-core cable).
7.2 Installation of supports and cables
In view that the intruder alarm engineer is mainly interest in PVC-sheathed wiring we will only focus our attentions on the supporting of this cable form being the mainstream practice. PVC-insulated and sheathed cables must of necessity be protected from mechanical damage in certain areas, and this has been considered. However, in some areas this is not essential as the cables may not be accessible or be concealed. They do, however, still need to be supported. The cables must be fixed at intervals as listed in Table 7.1.
Table 7.1
Spacing of cable supports for PVC-insulated cables in accessible positions
| Overall cable diameter (mm) | Horizontal (mm) | Vertical (mm) |
| <9 | 250 | 400 |
| > 9 but < 15 | 300 | 400 |
| >15 but < 20 | 350 | 450 |
| >20 but <40 | 400 | 550 |
Table 7.1 refers to cable supports in accessible positions, and this is by means of clips or saddles. PVC clips with a single hole fixing are most popular, with the internal surface of the clip being formed to suit the cable size and form. Self-adhesive clips can also be used where it is not possible to drive the nail fixing into position.
In the event that cables are installed in normally inaccessible positions and are resting on a reasonably smooth horizontal surface, then no fixing is necessary. However, fixing must be provided on vertical runs over 5 m.
When running in cables it is important to apply incombustible material to holes to prevent the spread of fire. Tubing should be used when negotiating sharp surfaces, including brickwork. Cables under floors must not be installed so that they can be damaged by contact with the ceiling or floor or their fixings. Cables passed through drilled holes in joists must be at least 50 mm vertically from the top or bottom and be supported by battens over extended runs.
Where cables pass through structural steelwork, holes must be fitted with suitable bushes to prevent abrasion.
The only other considerations are apparent, and require that care be exercised when removing the sheath of the cable and that this should be of the correct length to allow cables to be pushed back into position after terminating without too much tension or too much slack. Conductor ends must not be reduced as this leads to a loss of current-carrying capacity, and clamping screws must be well tightened.
We can conclude our observations on security wiring requirements by looking at their integration in Europe and summarizing some details. Cables are to follow contours. They must not be closer than 10.5 cm to any fixing point, such as the corner of a ceiling to wall, and be sited away from door frame uprights. They must also travel in straight lines and never diagonally across walls. They must be protected if likely to suffer damage, and when passed through roof spaces and between joists they should be encased in high-impact PVC or metal conduit. This is to reduce line faults and tampering potential. Jacketless cables are not to be used, and they should be sleeved in trunking with the same resistance to fire as the building material when passing through a floor or wall material or when buried. Cables are not to pass near steam or hot water pipes, and are to be at a reasonable distance to prevent any rise in surface temperature above the designed ambient temperature of the jacket.
Discussion points
Having considered Sections 7.1 and 7.2 and the options when considering an appropriate wiring system the installer must take a decision on the best practice with all factors taken into account. This ranges from protection to aesthetics for both mains and signal cabling. The decision to use steel conduit with its electrical continuity or an alternative non-metallic type of protection is important and will certainly differ between environments.
Once this has been established the consideration is that of connecting and terminating cables, and this forms the next stage.
7.3 Joints and terminations
Having studied the wiring requirements for security systems the need to join and terminate cables necessitates consideration. We know that installing multiple sensors of any type on a single detection circuit will increase the load and lack of cover in the event of a fault. We also realize that it makes fault finding more difficult. It is for this purpose that circuits are provided with an adequate number of test points in accessible positions, although they are best concealed. This clearly requires joints or splices, with an acceptable device being employed or the connections being soldered. However, there must be no identifiable markings on the cable sheath and no labelling should be applied although random colour coding should be used with the details held securely by the installation company. Acceptable methods for joining wire are:
Great care must be used with joints for two specific reasons:
(1) system resistance is increased and voltage drops can be caused with an inherent reduction in reliability;
(2) points are introduced where the system can be subject to abuse by bridging and tampering.
The normal interface between the electronic designer and the installer can be viewed as the wiring connections, be it a plug and socket, barrier strip, terminal block, tab connector, wire wrap, crimped sleeve or solder joint. Indeed, it is at this interface that so many installation and service problems originate. Copper is of course the normal material for interconnecting wire, but it can easily be damaged if excess screw pressure is placed upon it. Signal cabling is made up of several strands of fine-gauge wire rather than a single strand of heavier gauge. BT cable and mains supply cable, however, normally comprise a single conductor, and the technique of terminating it will be slightly different. Although we can provide the student with a description of the methods and practices that are available, in practice his or her ability to produce good connections will very much be governed by experience.
Mains connections
The cable to the intruder alarm is always best as an unjoined run derived from the consumer unit. However, there are junction boxes that can be used if the need arises. These must be placed in accessible positions and suit the load and cable. The sizes, current ratings and principal circuits are given in Table 7.2 for the domestic environment. The junction boxes will be of circular form and of 5, 15, 20 or 30 A capacity with three or four terminals of brass construction. They are often found in systems using twin and earth cabling.
Table 7.2
Sizes, current ratings and principal circuits. Mains connections
| Cable size (mm2) | Current ratings (A) | Circuits |
| 1.0 | 16 | Lighting |
| 1.5 | 20 | Lighting and 15 A single sockets |
| 2.5 | 28 | Ring circuits and 20 A radial circuits |
| 4.0 | 36 | 30 A radial circuits |
The method of connecting is simple in that like conductors are clamped together under the same terminal screw with earth insulation being applied over the protective conductor. The insulation for the phase and neutral conductors must only be stripped back as far as necessary, and the outer sheath must enter the junction box slightly before being stripped back. The important thing to remember about the supply connection as opposed to signal cabling is that with the former any bad or loose joint will lead to sparking, high resistance and the generation of heat that will eventually result in the destruction of the insulation. This can ultimately lead to fire or electric shock.
Wiring and BS 4737
BS 4737 states that the total resistance of all the circuits must be less than that which would reduce the voltage to below the required minimum at full load. The standard permits joints that are wrapped, crimped, soldered, clamped, connected by plug and socket or wire-to-wire and are either insulated or in a junction box. All wiring must be within the protected area, or where this is not possible then it must be mechanically protected.
The regulatory authorities require wiring to be protected against damage or tampering and for it to be of a neat and professional appearance.
Circuit wiring should be identified so as to facilitate future fault location with colour coding, but this can be varied with the code noted in a record book, and voltage drops on long runs must be considered. Junction boxes are to be fitted in complex circuits to allow circuit faults to be easily traced and be of an anti-tamper variety in high-risk situations. Open wiring can be secured by means of cable ties or by insulated staples, but runs are to be along the sides and top of architraves and in the lip of a skirting board or picture rail to avoid any damage being inflicted on the woodwork. Staple guns can be used but treated with caution to avoid damaging the cable insulation.
The engineer is therefore given some freedom with respect to the method of jointing to be employed, and can decide which method is best used in any given situation. Soldering requires technique, and is discussed separately.
Soldering
Soldering irons range from small gas-powered devices through to miniature soldering irons either powered by 12 V batteries or from the mains 240 V supply with ratings from 15 W up to the higher-capacity 50 W soldering stations.
The most commonly used solder is referred to as 60/40, being an alloy of 60 per cent lead and 40 per cent tin. Its melting point is low enough to allow safe soldering of most heat-sensitive electronic components, and is used with a non-corrosive flux that automatically cleans away oxides formed during the soldering process. It is available in a solder reel pack in different gauges to suit the parts to be soldered. The melting point is of the order of 190°C, and the gauges will be generally 18 SWG (1.22 mm) and 22 SWG (0.71 mm).
To actually perform the soldering process there are a few time-honoured tips:
• ‘Tin’ the soldering iron tip by melting a little solder on to it after first cleaning the surface area.
• Ensure that a mechanically strong joint has been obtained by twisting wires together so that when the solder is applied it will lock and seal the surfaces.
• Hold the iron to the joint for a short period to preheat the joint and add the solder to the joint. If the solder does not melt, withdraw the soldering iron and apply more heat to the wires.
A good solder joint is shiny and smooth. A bad ‘cold’ joint is dull and may also be rough. When joined wires are soldered, the solder should flow with a smooth contour to meet the wire at the ends of the joint; however, if it forms a blob with thick rounded ends the joint is not satisfactory.
An excellent level of mechanical strength can be obtained by a good soldered joint together with good electrical conductivity. The installation can then be complemented by the application of sleeving being drawn into position. To this end, heat-shrinkable sleeving can be applied which will shrink to a given percentage of some 20–50 per cent of its original diameter after the application of heat by a hot air blower or such. These sleeves have a high dielectric strength, resist attack by solvents and alkalis and can even provide a moisture-proof seal.
Crimping
The question of whether this is a better method of joining than soldering remains unanswered but we do know that a cold solder joint will not provide adequate electrical and mechanical characteristics. The engineer will need to use his or her own judgement. Certainly stranded wire crushes down well, so crimp-on connectors are held firmly. Crimping tools used correctly with the proper pressure being applied will provide good electrical and mechanical connections. There is a good range of crimping connectors available, and the task of applying them is certainly quick and easy.
Soldered and crimped connections are made up within tamper-protected junction boxes, but there is also a range of proprietary junction boxes specifically available for connecting cables. These boxes are in PVC with an anti-tamper lid, have countersunk back holes for fixing and screw terminals with which to clamp the wires being joined. They are available as 6, 8, 12, 20 and 24 way variants, and have break-outs for the cable entries. An addition to the range is the door loop version with its flexible integral silicone-insulated cord to allow placement of the wiring into moving doors.
Clamped joints
The considerations applying to the use of screw wrap terminals are apparent. Use special wire strippers to remove the cable insulation. After stripping, twist the bared wire in the same direction as its natural twist to prevent any stray strands. Use only a clockwise wrap under the screw heads making sure that only some 1 mm of bare wire is exposed beyond the screw head. Always support the wire when tightening any screws on to them. Ensure that the conductor is firmly gripped but not overtightened or damaged. Do not let the outer sheath be removed outside of the junction box, and ensure that the correct amount of slack is allowed within the enclosure and that the wires are not trapped by the lid or are pulled tight when the lid is resited. These considerations are very elementary and do not need elaboration, but when correctly performed, good electrical characteristics and mechanical strength are achieved.
There are of course a huge variety of other forms of clamp, but the normal procedures apply with all screw forms whether the screw is applied direct to the joint or applies a spring leaf against the connection.
Splicing
The definition of the splice, which is acceptable according to BS 4737 is that of a joint essentially made by tightly winding the ends of two wires together for a short distance and then mechanically restraining it by an acceptable method such as soldering, crimping or sleeving.
Discussion points
With the progression towards more complex wiring and in cases of longer wiring runs there is a need to apply joints to facilitate fault finding. The provision of any joint creates a multitude of considerations, and the engineer must balance these against his or her capacity to perform satisfactory connection techniques.
7.4 Fixing methods for devices
The method of fixing is very much dictated by the device that is to be installed and the material that it is to be affixed to. In many cases manufacturers supply fixing devices such as plugs and screws to guide the installer, and this is very much the case with most external sounders. These of course have their own requirements and can be considered at the outset.
External audible intruder alarm signalling devices
The manufacturer will often provide guidance, but these devices should be fitted as high as possible to reduce the possibility of interference by an intruder. The position may also depend on a number of factors which can affect the ability of it to be heard (or seen in the case of a visual warning device). It therefore should be located in a position where it may be easily viewed. The device should not face heavy traffic or a railway as this will affect the ability of it to be heard at a relatively short distance. The wiring to it should enter direct through the wall and not be surface mounted.
System alarms are divided into bells and sirens, although bells are certainly going out of style. The construction of external audible alarms is governed by the standards applicable to the extent that they must be totally enclosed and weatherproof with a case offering at least the same protection afforded by 1.2 mm of steel. They must also produce at least a 70 dB(A) mean sound level and 65 dB(A) in any one direction at 3 m with the security cover in place. These sounders are liable to be pulled from walls, and therefore must rest on a solid structural base of concrete, brick or hardwood, which will also prevent some of their power from being absorbed through vibration of the building medium.
Therefore, they must be sited to give maximum prominence and sound output yet have reasonable protection from accidental or wilful damage but still provide access for servicing.
The surfaces to which an external sounder may be affixed will vary enormously, and the minimum requirements for typical surfaces are described below.
Brick walls
Three No. 10 screws in suitable plugs penetrating the actual brick to a depth of at least 40 mm should be used.
Metal, wood or thin skinned structures
Bolts with backplate are required for these surfaces.
The first type of fixing is straightforward and there is a huge range of screws and plugs available. The screws are available with different head forms and finishes and even with high-tensile characteristics. In installations where the wall structures are irregular it is advisable to seal around the enclosure backplate with cement to make it more difficult for the intruder, who may attempt to insert a jemmy behind the sounder in order to prise it from its fixings.
The second type of application is encountered on prefabricated buildings. In these instances it is normal practice to use a hardwood backplate which is initially fixed to the building structure using bolts with washers and nuts. The cable is brought through this backplate via grommets, and the sounder is also bolted through the backplate and building medium. When carrying out this task the backplate is best fixed in place initially and then further bolts used to secure the sounder rear housing. The sizes of the bolts and backplate depend on the application and its vulnerability, but, as a minimum, a sheet of 20 mm hardwood with 6 mm bolts, steel washers and steel full nuts or nylon insert locking nuts is practical. The heads of the nuts will be protected by the sounder enclosure to stop any attempt at removal.
Remote signalling equipment
Remote signalling equipment is required to be within a secure area that is not visible from outside of the building. Its housing must have the same resistance to attack as a control panel and have appropriate anti-tamper devices to prevent it being removed from its fixing without generating an alarm. The housing must be securely fixed in position. Due to these requirements these devices are often installed within cupboards, but such areas may not have solid walls and can often be of cavity construction.
So what are the different wall types that must be accommodated?
Solid walls
General-purpose wall plugs can be used with appropriate screws (Table 7.3). Where more heavy duty fittings are required, heavy duty wall plugs intended for brick, concrete, breezeblock and cellular block or stone should be considered. These will use, in general, a 7 mm drill bit and accommodate screw sizes Nos. 8–14. Dry-lined walls also fall into this category (plaster board attached by spot adhesive to a solid backing wall).
Partition/cavity walls
The position of the wooden framework should be established, and long screws used to fix equipment to this structure. Heavy duty plasterboard plug fixings can be used as a supplement. These are specific plugs intended to fix to cavity and plasterboard partitions. Alternatively, super toggle cavity anchors can be adopted. These have screw-tensioned nylon anchor arms which self-adjust to the wall thickness and provide a strong method of fixing for cavity walls. For an even more superior mounting, cavity fixing spring toggles can be used. These are designed for use with plasterboard, lath and plaster and other partition materials. These feature a strong grip and have wide span wings, and are installed as shown in Figure 7.1. Bolt sizes can be up to M6 (6 mm).
Stone walls
A strong fix to stone walls can be made using general-purpose wall plugs or the heavy duty variant. The main consideration is to ensure that the plug is entering stone work and not loose or soft surrounding plaster or cement. Often, longer screws are needed to reach the stonework because of irregularities in the wall.
The conclusion to fixing is to remember that the wall medium must be suitable and that the screws of the correct length are used to reach far enough into any plugs to ensure that they cannot be pulled from their location.
7.5 Working equipment: safe use
The Health and Safety at Work Act 1974 (HASAWA)
The very first health and safety legislation in the UK was passed as early as 1802. Over the years, a great many pieces of legislation were passed, although much of this was very confusing. This was clarified in 1974 when the HASAWA was introduced. Its first major significance was that it covered everyone at work whatever the workplace with the exception of staff in domestic premises. The Act placed clear duties on everyone, employer, employee, the self-employed, manufacturers, suppliers and installers.
The main purpose of the Act is to promote good standards of health and safety, so preventing people coming to harm at work. It makes health and safety an essential part of work, not an option. It does this by placing statutory duties on employers and employees to build into their work safe practices. It does not give step by step instructions on how to do this, but details can be found in regulations made under the Act. Examples of this are the Electricity at Work Regulations 1989 and the First Aid Regulations 1981. The Act is proactive and not reactive, and the framework that it sets up allows for the ongoing process of developing health and safety legislation by updating older regulations and issuing new regulations, some of which originate from the EC.
Most of the responsibility for health and safety falls on employers. They must ensure the health safety and welfare of their employees by:
• providing safe systems of work, safe environments and premises with adequate facilities;
• provide safe access and egress to and from the workplace;
• provide appropriate training and supervision;
• provide information to the employees;
• have a written health and safety policy if there are five or more employees;
• provide safe plant, machinery, equipment and appliances and safe methods of handling, storing and transporting materials.
Employers must also make sure that their activities do not endanger people who visit the workplace or members of the public.
Employees have a duty to take care of themselves as well as anyone else who may be affected by what they do at work. They must also cooperate with the employer on health and safety matters by following rules and procedures.
The self-employed are covered in much the same way, with a duty to ensure that they do not endanger themselves or others by their work activities. The installer working in a private house is governed by the same rules that would apply in a large industrial building, and he or she must therefore:
• design and construct a safe product;
• test the product for safety;
In so far as safety is concerned, a lot is down to common sense, and accidents can be avoided by being aware of hazards and by following established rules and practices. Some human factors that may cause accidents are:
It follows that an employer has to ensure that persons are properly supervised at work, are trained correctly and understand safety procedures. Some tasks have obvious hazards, and within the intruder industry working at a height on poorly maintained access equipment or working with poorly maintained power tools will always create problems.
Ladders
Figure 7.2 shows a set of ladders tied securely and at the correct angle. It has been found that more than half of the accidents involving ladders occur because they are not securely fixed or placed, and indeed most of these accidents occur when the work is of 30 minutes duration or less. It is apparent that most of this is down to haste. Certain considerations apply when using ladders:
• Support the foot on a firm level surface. Never on loose material or other material to gain extra height.
• Do not tie shorter ladders together to obtain the desired height.
• When possible, secure the top of the ladder using clips, lashings or straps.
• Alternatively, secure at the base using blocks, cleats, sandbags or stakes embedded in the ground. Note that ‘footing’ is not considered effective for ladders longer than 5 m.
The safe use of ladders also involves the following:
• Make regular inspections of them.
• Never carry out makeshift repairs.
• Never paint wooden ladders as this can hide defects. Clear varnish may be used.
• Beware of making contact between aluminium ladders and live electrical cables.
• Ladders should extend at least 1.05 m above the highest rung being stood upon.
• The angle of use should be 75° to the horizontal and 1 m for every 4 m in height.
• If the ladder is erected near a doorway it must face the door, which is to be locked shut or secured open. The base must also be fenced off to prevent others walking under it.
• Never allow more than one person at a time to be on a ladder.
• Never consider the ladder as the best device for all applications: it may be safer to work from a securely constructed scaffold tower.
Tools and lifting materials
Do not carry heavy items up a ladder. Use a rope or hoist. Carry tools in a bag or belt holster to enable the free use of both hands to secure a firm hold.