Wiring system

        This work is focused on enlightening us about Electrical wiring system.  In general, Electrical wiring refers to insulated conductors used to carry electricity and associated devices. This paper describe general aspects of electrical wiring used to provide power in buildings and structures as can be  referred as building wiring.

       Wiring safety are intended to protect people and property from electrical shock and fire hazards.

    Regulations may be established by city, country, provincial/state or national legislation usually by adopting technical standard set by the organization, or by a national standard electrical code.

 

              INTRODUCTION

     A Wiring system is an assemblage of parts used in forming an electrical wiring circuit. It consists of the conductors together with its insulation, mechanical protection and certain accessories for fixing, joining and terminations.

     In all systems the running of wiring should be planned beforehand and, in many cases, marked out on the site.

   To arrive at the best system to use in any particular situation, some or all, of the following factors should be taken into account;

 The conditions, which the installation must with stand (e.g  whether likely to be subjected to mechanical damage,moisture,fumes,weather or to abnormal or subnormal temperatures).

  The conditions under which the work will have to be carried (whether likely to be in a new building under construction or in fully occupied premises)

  Appearance (e.g whether required to be visible, concealed or buried) .

  Whether provision should be made for future alterations or additions.

  Durability

  Cost

  Time available

 

 

Types of Wiring

  Surface wiring

  Concealed Surface Wiring

  Concealed or Conduit Wiring

 Trunking wiring

 

        An important   feature of the installation is that it fits into the building structure without causing unsightliness and too  much interference or damage to the building itself. The various wiring operations should be carried out at the correct stage in the erection of the building to avoid unnecessary cutting, drilling and removing of the fabric of the completed building.

    

            Method of Installation of Wiring Systems.

  Steel Conduit

  Mineral Insulated Metal SheathedCable(MIMSC)

  Cable Trunking

  Over head bus bar

    When installed on the surface, they are fixed in position by hardened PVC cable clips, which are fitted with a hardened nail suitable for driving into most surfaces. Distances between clips for the common sizes should be around 300mm for horizontal runs and 350mm for vertical runs. Any bends made in the cable should have a minimum radius as, given in the I.E.E regulations.

 

  Steel Conduits

     Cables provided with insulation only, cannot be run for fixed installations without further overall protection against mechanical damage. In situation where there is likelihood of greater mechanical damage to the wiring system,  such as industrial and some commercial installations, steel conduit provides a suitable method of protection. The use of fittings such as bends, tees, through-boxes, four- way boxes, terminal boxes etc .,

 

        If the conduit system is installed correctly with inspection boxes at the correct points and distances apart, it is possible to rewire the complete installation without dismantling any part of it. For this reason, the conduit should be erected and fully completed before any  cables are drawn in.

         Under conditions of high ambient temperature (over 65°C),the conduit can be wired with buty1-insulated cables, which will withstand temperatures of up to 80°C. For temperatures up to 145°C, Silicon rubber insulated cables can be used.

     Standard sizes of conduits are 20mm, 25mm, 32mm which are the external diameters. Above these sizes, the conduit becomes difficult to cut, bend and thread and the use of cable trunking is advisable. The conduit is annealed to allow bending and setting without fracture, but suitable formers supporting the tube walls should be used when bending to prevent distortion of the shape.

 

number of cables)to be drawn in. In order to prevent overheating of cables in conduits, the space factor should not exceed 40%.

Erection of Conduits

Modern conduits are of the screwed type (conduit threads)and are obtained in four meter lengths with each end threaded. For joining lengths together, a coupler is used, which consists of a short length of tube with an internal conduit thread . The fittings are provided with internally threaded “spouts” for connecting the conduits. On higher quality installations, the use of circular inspection – type boxes or fittings is preferable as it allows for easier and more convenient wiring with less danger of damage to cables when being drawn in. All conduit fittings and boxes should be securely fixed in position and the conduit supported along its run by “saddles”. saving time and

 

MINERAL – INSULATED METAL SHEATHED CABLES

    These consists of solid, pliable, circular copper conductors positioned in a highly compressed magnesium oxide powder. They have a much higher working temperature than PVC or rubber – insulated cables, which makes them ideally suited for use in boiler rooms and other temperature situations.

 

CABLE TRUNKING

    Where large numbers of cables are to be run it is more economical to enclose them into trunking of suitable size than to install a lot of conduits. Trunking is made from mild steel or plastic material . The standard sizes are 50mmx50mm, 75mm x 75mm and 100mm x 100mm . They are provided in three meter lengths and can be bolted together  by fishplates. At all joining points, a copper strip is bolted across to ensure efficient earth continuity. Separate compartments can be fitted into one trunking where segregation of wiring cables is required.

   

    Where trunking is run on its side, it should be fitted with clips to prevent the cables from falling out when the cover is removed. Vertical runs should be fitted at intervals with cable support “pins” to prevent the weight falling on one point .

    I.E.E.E & N.I.E.E Regulation require a space factor of 45%. Both manufacturers and the I.E.E publish tables from which the maximum number of various size cable laid in the trunking may be calculated. Each size of cable is allotted a number.

 

 

   The supplies for equipment and accessories to be fitted on the perimeter walls and partitions themselves can be taken from skirting trunking, which joins up with the floor duct system. When the duct system is completed, it can be screeded over with a mixture of sand and cement around 50mm to 100mm thick, on top of which the floor finish can be laid.

       OVER HEAD  BUS – BAR TRUNKIING

   This consist of a substantial metal  trunking, which  contains copper bars fixed in position by   insulated supports. It is a very convenient system of wiring in industrial installations where equipment and machines are frequently moved around as production requirements change

 

   They are installed in rooms, cubicles or cupboards having provisions for locking arrangements so as to safeguard them against operation by unauthorized  personnel.

    Adequate illumination shall be provided for all working spaces within the switch boards when installed indoors.

    They shall not be installed above gas stoves  or sink or within 2.5m of any washing unit in the kitchen or washing room.

    They are totally enclosed or flame- proof if they are to be installed in damp or dust or flame able  areas.

 

    Location of Branch distribution boards;

    They shall be located as near as possible to the centre of the load they are serving.

    They shall be mounted on walls and shall be accessible for replacement of protective devices and switching  “off” during emergency.

    They shall be placed so as not to affect the esthetic of such environment.

 

  SWITCH GEARS

They are devices for engaging or disengaging two contact points. In electrical systems, they include switches, contactor, isolators, circuit breaker and solid bars.

In most cases, they are automatic.

  CIRCUIT BREAKERS

       Circuit breakers are protective device that operate either manually or automatically to open or close a contact point . They are mainly of electromagnetic type and carry various current levels.

 

  Molded case circuit breaker (MCCB);

        They are designed for circuit protection in low and medium voltage distribution system . They are used mainly for short rapid protection which is achieved by rapid magnetic tripping. They  are extremely compact and are designed for use in control panels, switch boards or in separate individuals enclosures particularly for applications in distribution feeders, commercial building and industrial panels.

 

  SWITCH FUSE;

    This is an extension of isolator, in that the load side of supply is interrupted by a fuse in the phase conductor .

 FUSE LINK;

    It protects the equipment and parts of the system against the dynamic and thermal effect of short circuit currents. It breaks the continuity of the current when excessive one flows due to faults.

  REWIREABLE FUSE

     A rewireable fuse consist of a fuse link, holder and fuse carrier. The holder and carriers are made of insulating materials. The fuse link or wire is replaced with correct size when it is melted.

  CARTRIDGE FUSE;

    A cartridge fuse consists of a porcelain tube and metal caps to which the fuse element is attached. The tube is filled with silica substance , the whole system is replaced when blown.

 

   HIGH RAPTURING CAPACITY FUSE

    The HRC fuse is an improved cartridge fuse and is normally found in motor circuits and industrial panels.

   EARTHING;

    Earthing is the act of connecting an electrical system or equipment to the earth with the help of a connecting wire of negligible resistance, it is what we do to avoid  undue shock caused by fault in electrical system/component.

   NEEDS FOR EARTHING ;

   Proper earthing is very important in electrical systems. It is mainly ;

To protect personnel against electric shock.

To protect property against fault caused by electrical disturbances, lightening and failure of equipment connected to the wiring system

To provide protection against dangerous voltage equipment both in telecommunication building and subscribers premises.

 

To limit cross – talk ,noise and interference in telecommunication equipment  to a prescribed value.

To ensure certain functions of telecommunication systems which have earth return paths.

  SYSTEM EARTHING.

   This means the connection of the neutral conductor of the wiring system to  the earth. Its aim is to drain off any excessive voltage that may accidentally enter the system as a result of electrical disturbance, lightening or insulation breakdown

 

                           CONCLUSION    

 

Ø     In every Electrical installation, it is very necessary to carry out some test to ensure that all conductors, cables and electrical equipment have been installed and connected correctly in accordance with IEE Wiring regulations for Electrical installations. The regulations states that a number of test have to be carried out before a supply of electricity is  given to a  consumer and that the tests, where relevant, and  should follow a definite sequence. Note; The  IEE Wiring regulation point out that if any test fails to comply, it must be rectified and taken again.

 

REFRENCES

Craft, Terrel (1915) Wiring of finished building