Building Services

Water Supply

Water supply systems receive water from the sources such as lakes, rivers, reservoirs, wells or sea through desalination. Water is pumped from the source and then it is sent to the treatment plant for purification. After purifying, it is sent to the elevated tanks for distribution. Water is distributed through a distribution network to the houses.

Water Supply Network
A water supply network consists of following;

1. the watershed or geographic area that collects the water;
2. a raw (untreated) water reservoir where the water gathers, such as a lake, a river, or groundwater from an underground aquifer;
3. A pumping system and transmission system to the treatment plant.
4. water purification system such as a water treatment plant;
5. transmission from treatment, through pipes to treated water storage, that may be either elevated or ground level; and
6. Distribution through piping/water mains from storage to consumption (at houses, fire hydrants, industrial use points, etc).

Reservoir
Reservoirs are created first by building a sturdy dam, usually out of cement, earth, rock, or a mixture. Once the dam is completed, a stream is allowed to flow behind it and eventually fill it to capacity.

Water Intake and Pump house

Water will be pumped from reservoir at the intake.

Raw water Transmission main

Raw water will be transmitted to the treatment plant through transmission main. DI or UPVC pipes will be used for this purpose.

Treatment Plant

Traditional surface water treatment plants generally consist of three steps: clarification, filtration and disinfection. Clarification refers to the separation of particles (dirt, organic matter, etc.) from the water stream. Chemical addition (i.e. alum, ferric chloride) destabilizes the particle charges and prepares them for clarification either by settling or floating out of the water stream. Water will then be sent through a filtering system removing smaller particulate matter. The preferred method of disinfection is via chlorine addition. Chlorine effectively kills bacteria and most viruses. From the treatment plant water is sent to a water tank for the purpose of distribution.

Water tower

Water tower is a very large elevated tower that is constructed for the purpose of holding a supply of water at a height sufficient to pressurize a water supply distribution system.

Distribution of water

Water will be distributed to the houses through distribution system.

Within this water supply network, water should be properly cleaned and appropriate pressure should be created for distribution.

Water Distribution system within the building

Water is distributed for various consumption purposes in a building through internal water distribution system. In every building, adequate quantity of water should be available at required locations to meet various needs of the occupants.

Water is supplied by the ‘Statutory water undertaker’ required to supply a constant, potable (drinkable) supply of water for which water rate is charged by meter.  Connections to the existing main are made by the water undertaker. The house or building service pipe connection is made to the main and the service pipe is run to a stop valve near to the site boundary of the building to be served. The pipe that is run from stop valve in to the building is termed as supply pipe. The supply pipe is run in to the building normally underground as shown in the Figure.

Cold Water Supply Systems

The two systems of cold water supply that are used are cistern feed and mains pressure.

Cistern feed system (Indirect system)

In the cistern feed system, water is supplied to a cistern (overhead tank) through a supply pipe. A cistern is a liquid storage container which is open to the air and in which the liquid is at normal atmospheric pressure. Cistern is made from Galvanized steel, stainless steel, plastic, masonry or concrete.

The water supply to the cistern is controlled by a ball valve that is fixed to the cistern, above the waterline, and connected to the cold supply through a valve. As water is drawn from the cistern the ball falls and the arm activates the ball valve that opens to let water in to the cistern. When water has risen to the water line, marked on the cistern wall, the ball and arm rise to close the valve.

Cistern feed cold water distributing pipe system

Figure illustrates the cold water distributing pipe system for a two storey house. The distributing pipe is connected to the cistern some 50mm above the bottom of the cistern to prevent any sediment that may have collected from entering the pipe. A stop valve is fitted to the pipe adjacent to the cistern, isolating the whole system from the cistern in the event of repairs and renewals. The distributing pipe is carried down inside the building with horizontal branches to the first flow and ground floor fittings, as shown in Figure. The aim in the layout of the pipe work is economy in the length of pipe runs, and on this depends a sensible layout of sanitary fittings.

            

Cistern Feed Hot water supply

Figure 3 illustrates the hot water distributing pipe system for a two storey house. The hot water is drawn from a cylinder which is fed by cold water drawn from the cold water storage cistern in the roof.

The cold water in the hot water cylinder is heated by a heat exchanger in the cylinder through which hot water circulates from the boiler. The cold water feed to the cylinder is run through a stop valve to the bottom of the cylinder.

                         

Mains Pressure Cold& Hot Water Supply

Illustrates the cold water, mains pressure pipe system to a two storey house.

Water supply in High Rise Buildings

For medium and high rise buildings, there is often insufficient mains pressure to supply water directly to the upper floors. Boosting by pump from a break tank is therefore usually necessary and several more of these tanks may be required as the building rises, depending on the pump capacity.

                                                                    A break pressure cistern is also required on the down service to limit the head or pressure on the lower fittings to a maximum of 30 m (approx. 300kPa). A pressure reducing valve is sometimes used instead of a break pressure cistern. As the tank empties and the water reaches a predetermined low level, the pipeline switch engages the duty pump.

A float switch in the break tank protects the pumps from dry running if there is an interruption to mains supply. The various pipe sections are fitted with isolating valves to facilitate maintenance and repairs.

Smaller hydro pneumatic tanks can also be used to help control pressure booster pumps, allowing them to be cycled on and off by a pressure switch. The captive air within the tank keeps the system pressurized while the pump is off. When the water pressure drops to the “on” pressure setting, the pump starts and raises the volume and pressure of the water in the tank. If some air is absorbed by the water, as this occurs, a float switch detects the high water level in the cylinder and activates an air compressor to regulate the correct volume of air.

Estimation of water requirements

Requirements regarding water supply for residence should be assumed as 135 Ltrs per head per day. Water Requirements for buildings other than residencies are as follows:

Table 1 –Water Consumption

Type of Building	Rate per head per day Ltrs
Factories where bathrooms are required to provide	45
Factories where no bathrooms are required to be provided	30
Hospitals ( including laundry ) per bed ü  No of beds not exceeding 100 ü  No of beds exceeding 100	340         450
Nurses homes and medical quarters	135
Hostels	135
Hotels ( per bed )	180
Offices	45
Restaurants ( per seats )	70
Cinemas, concerts, theatres ( per seat )	15
Schools ü  Day schools ü  Boarding schools	45          135

Water Supply Fittings

For water supply to a building, PVC pipes or Galvanized iron pipe is used. Sizes of the pipes depend upon factors like, head of water, population to serve etc. For laying pipe lines following attachments are generally used.

Ø  Sockets:  They are required to lengthen the pipe line.

Ø  Bends:    These are used to give necessary bend to the pipe line.

Ø  Elbow:    These are used to give 90⁰  turn to the pipe line.

Ø  Water Tap: It is provided at the ends of pipe lines in order to release the water.

Ø  Stop tap: It is used to control water inside the pipe line.

Rate of water flow

The rate of water flow at taps and outlets depends on the diameter of the outlet and the pressure of water at the tap or outlet. The water pressure depends on the source and the loss of pressure to the frictional resistance of the pipe work and its fittings such as elbows, tees, valves and taps. The design of pipe work installation is concerned, therefore, with estimating the resistance to flow and the selection of the pipes of sufficient size to allow a reasonable rate of flow at taps, where the source of water pressure is known. In calculating pipe sizes we can assume that all the taps served may be opened simultaneously, and the pipes are sized accordingly. In large installations such as those of multi-storey blocks of flats, it is unlikely that all taps will be open at the same time and a frequency of use assumption can be made to avoid the expense of over large pipes.

House Drainage

The arrangement provided in a building, for collecting and conveying waste water through drain pipes, by gravity, to join either a public sewer or a domestic septic tank, is termed as house drainage.

Aims in the house drainage:

1. To maintain healthy conditions in the building
2. To disposed off waste water as early and quickly as possible
3. To avoid the entry of foul gases from the sewer or the septic tank
4. To facilitate quick removal of foul matter ( eg. Human excreta )
5. To collect and remove waste matters systematically

Principles of house drainage

Design and construction of a house drainage system is controlled by the following general principles.

1. House sewers or drains should be laid as far as possible by the side of the building rather than below the building
2. The lavatory blocks should be so located that the length of the drainage line is minimum. In the case of multistory buildings they should be located one above the other.
3. The size of the drain should be adequate.
4. The slope of the drains should be sufficient to develop self cleansing velocity.
5. As far as possible, drains should be laid in straight lines between successive inspection chambers. All sharp bends and junctions should be avoided except through chambers or manholes.
6. The drain should be laid at such a level that the lowest level of the building may drain in it.
7. The house drain should be disconnected to the public sewer by the provision of an intercepting trap. This will avoid the entry of foul gases from entering the house drainage system.
8. The entire system should be properly ventilated from the starting point to the final point of disposal.
9. Drain should be non- absorbent type, laid on good foundation, and protected against external loads.
10. All the joints of sewers should be made water tight.

Trap

A trap is located below or within a plumbing fixture. It is used to prevent sewer gases from entering buildings. Because of its shape, the trap retains a small amount of water after the fixture's use. This water in the trap creates a water seal that prevents sewer gas from passing from the drain pipes back into the occupied space of the building. Essentially all plumbing fixtures including sinks, bathtubs, and toilets must be equipped with either an internal or external trap.

Characteristics of a trap

A trap should posses the following characteristics:

1. It should possess adequate water seal at all times, to fulfill the purpose of its installation. However, it should retain minimum quantity of water for this purpose.

2. It should be of non absorbent material

3. It should be free from any inside projections, angles or contractions, so that flow is not obstructed or retarded.

4. It should be self cleansing

5. Its internal and external surfaces should be smooth so that dirt does not stick to it.

Classification of traps

Traps are classified as follows:

Classification according to shape:

P-trap – This resembles the shape of the letter P, in which the legs are at right angles to each other.

Q-Trap - This resembles the shape of letter Q, in which the two legs meet at an angle other than a right angle

S – Trap – This resembles letter S, in which both the legs are parallel to each other, discharging in the same direction.

Classification according to use:

Floor Trap – It is provided at the point of entry of waste water in the house. It will be placed in bath rooms, kitchens, sinks etc. A floor trap forms the starting point of waste water flow.

Gully Trap – Gully trap forms the beginning point of horizontal flow of sewage. It is normally installed near the external face of the wall and it is kept slightly higher or even in line with the pavement or ground. This trap takes sewage , either to sewer  or to inspection chamber or to manhole.

Intercepting traps – This trap has comparatively deeper water seal. It is provided at the last inspection chamber or manhole of the house drainage system. Sewage coming from the house enters public sewer after passing through intercepting trap. The main idea of providing the intercepting sewer trap is to prevent the entry of sewer gases from public sewer line in to the house drains.

Siphonage

Sewer pipe is normally at neutral air pressure compared to the surrounding atmosphere. When a column of waste water flows through a pipe, it compresses air in the pipe, creating a positive pressure that must be released or it will push back on the waste stream and downstream traps' water seals. As the column of water passes, air must flow in behind the waste stream or negative pressure (suction) results. The extent of these pressure fluctuations is determined by the fluid volume of the waste discharge.

Excessive negative air pressure, behind a 'slug' of water that is draining, can siphon water from trap seals at plumbing fixtures. Generally, a toilet outlet has the shortest trap seal, making it most vulnerable to being emptied by induced siphonage. An empty trap can allow noxious sewer gasses to enter a building.

On the other hand, if the air pressure within the drain becomes suddenly higher than ambient, this positive transient could cause waste water to be pushed into the fixture, breaking the trap seal, with dire hygiene and health consequences if too forceful. Tall buildings typically three or more stories, are particularly susceptible to this problem. Vent stacks are put in parallel to waste stacks to allow proper venting in tall buildings

Systems of Plumbing

Four principal systems of plumbing that use for drainage of buildings is given below

1. Single stack system
2. One pipe system
3. One pipe system partially ventilated
4. Two pipe system

1.     Single stack system

In this system, only one vertical soil pipe is used. The wastes from baths, sinks etc, as well as foul matter from the WC are discharged in one single pipe, called the soil and waste pipe. There is no separate pipe for ventilation purposes. This system proves economical as only one pipe to be provided. The effectiveness of the system totally depends on the depth of water seal. No water seal should be less than 75mm.

2.     One pipe system

In this system, a separate vent pipe is provided and the traps of all water closest, basins etc are completely ventilated. Waste connections from sinks, baths, wash basins and the soil pipe branches from W.Cs. and urinals are all connected in to one main pipe.

Since all the traps are ventilated by a separated vent pipe, this method proves to be more effective than the single stack system.

3.     One pipe partially ventilating system

This is modified form of the single stack system and one pipe system. In this system, the waste from W.C., basins, sinks etc is discharged in to one common soil and waste pipe. However in addition, a relief vent pipe is also provided which provides ventilation to the traps of water closets. The traps of basins etc are not directly connected to the vent pipe.

4.     Two pipe system

In this system, separate soil pipe and waste pipe are provided. The discharge from W.C. is connected to the soil pipe while the discharge from baths, sinks, lavatory basins etc, are connected to the waste pipe. All the traps are completely ventilated by providing separate ventilating pipes. Soil pipes and waste pipes are provided with separate vent pipes. The system thus requires four pipes and hence proves very costly.

Drain System outside the building

Man holes

The traditional arrangement for inspecting, testing and clearing blockages in underground drains is the inspection chamber or man hole. The man holes may be constructed by bricks or cement concrete. The manhole is located at those places where drain blockages are most likely to occur.

Septic System

           

Septic system is a used to treat waste water where main sewers maintained by authorities are not available.

A typical septic system has four main components: a pipe from the home, a septic tank, a drain field, and the soil. Microbes in the soil digest or remove most contaminants from wastewater before it eventually reaches groundwater.

Pipe from the home

All of household wastewater exits home through a pipe to the septic tank.

Septic tank

The septic tank is a buried, watertight container typically made of concrete, fiberglass, or polyethylene. It holds the wastewater long enough to allow solids to settle out (forming sludge) and oil and grease to float to the surface (as scum). The settled solids are an aerobically digested reducing the volume of solids. Compartments and a T-shaped outlet in the septic tank prevent the sludge and scum from leaving the tank and traveling into the drain field area or soakage pit.

Drain field

The wastewater exits the septic tank and is discharged into the drain field for further treatment by the soil. The partially treated wastewater is pushed along into the drain field for further treatment every time new wastewater enters the tank.

Seepage pit/Soakage pit

An alternative to the common drain field is the Seepage Pit (Dry Well). In this type, liquid flows to a pre-cast tank with sidewall holes, surrounded by gravel. (Older versions usually consist of a pit with open-jointed brick or stone walls.) Liquid seeps through the holes or joints to the surrounding soil.

Soil

Septic tank wastewater flows to the drain field, where it percolates into the soil, which provides final treatment by removing harmful bacteria, viruses, and nutrients. Suitable soil is necessary for successful wastewater treatment.

Failure of septic tank system

There are two main factors that cause problems: overload and lack of maintenance. An overloaded (or under-designed) septic system can occur if, for example, an original two bedroom home has subsequent bedroom and bathroom additions, but no increase in septic system capability. With overload, waste water flows to the leach field before there has been time for natural biological process to settle out solid waste in the septic tank.

                                                          As a result, particles can clog up the holes in the drain-field pipes and build up extra pressure on the holes that remain open. The increased flow through fewer drain holes produces more liquid than the soils of the leach field can naturally treat. The result can be contaminants moving to the ground water, rise of waste water to the surface, or both. In the case of subsurface overload, the situation may go unnoticed for years.

Lack of maintenance can also lead to problems even if the system is not overloaded. If the solid material is not periodically removed from a septic tank there could be insufficient room for solid matter to settle out. In such cases, solid material may also clog parts of the drain field. If the septic system is both overloaded and the septic tank full with solids, then there can be a real risk of environmental degradation.

Sanitary appliances

Sanitary appliances, sometimes termed sanitary fittings, include all fixed appliances in which water is used either for flushing foul matter away or in which water is used for cleaning, culinary and drinking purposes. The former, termed soil appliances, include WCs and urinals, the discharge from which is described as soil, or soiled or foul water. The second type, termed waste appliances, include wash basins, baths, showers, sinks and bidets, the discharge from which is described as waste water.

HVAC System

HVAC systems are any systems that deal with heating ventilation and air conditioning.

The three functions of heating, ventilating, and air-conditioning are closely interrelated. All seek to provide thermal comfort, acceptable indoor air quality, and reasonable installation, operation, and maintenance costs. HVAC systems can provide ventilation, reduce air infiltration, and maintain pressure relationships between spaces.

Ventilation

Building ventilation is the process of bringing outdoor air into a building, circulating it, and later purging it to the environment. The main purpose of ventilation is to provide acceptable indoor air quality by diluting and removing contaminants from the indoor air. Building ventilation is achieved by natural or mechanical means, or by a combination of the two. Mechanical ventilation is the use of mechanical air handling systems—commonly referred to as heating, ventilation, and air conditioning (HVAC) systems—to ventilate buildings.

Thermal comfort

Human thermal comfort is the state of mind that expresses satisfaction with the surrounding environment. Air temperature, relative humidity and speed of air movement are some of the important factors affecting to thermal comfort. Maintaining thermal comfort for occupants of buildings or other enclosures is one of the important goals of HVAC systems.

Heating Systems

Furnaces and Boilers

Most U.S. homes are heated with either furnaces or boilers. Furnaces heat air and distribute the heated air through the house using ducts; boilers heat water, providing either hot water or steam for heating.

Electric Resistance Heating

A type of heating system where heat, resulting when electric current flows through an "element" or conductor, such as Nichrome, which has a high resistance, is radiated to a room.

Air Conditioning

The term air conditioning refers to the cooling and dehumidification of indoor air for thermal comfort . In a broader sense, the term can refer to any form of cooling, heating, ventilation or disinfection that modifies the condition of air.^[1] An air conditioner is an appliance, system, or mechanism designed to stabilize the air temperature and humidity within an area (used for cooling as well as heating depending on the air properties at a given time), typically using a refrigeration cycle.

Basic Refrigeration Cycle

In this cycle, a circulating refrigerant such as Freon enters the compressor as a vapor. Then, the vapor is compressed and exits the compressor superheated. The superheated vapor travels through the condenser which first cools and removes the superheat and then condenses the vapor into a liquid by removing additional heat at constant pressure and temperature. After that, the liquid refrigerant goes through the expansion valve (also called a throttle valve) where its pressure abruptly decreases, causing flash evaporation and auto-refrigeration of, typically, less than half of the liquid. That results in a mixture of liquid and vapor at a lower temperature and pressure. The cold liquid-vapor mixture then travels through the evaporator coil or tubes and is completely vaporized by cooling the warm air (from the space being refrigerated) being blown by a fan across the evaporator coil or tubes. The resulting refrigerant vapor returns to the compressor inlet to complete the thermodynamic cycle.

HVAC systems

Most HVAC systems are powered by air conditioning units and furnace units. In some cases, one or the other may be the only one present. For example, at higher latitudes, it is common for older homes to have only a furnace. Air conditioning is not needed during many times of the year and was considered a needless luxury. In some other countries, heating system will not be useful during most of the time of the year.

AC systems

1)     Window air conditioner: This is the most commonly used air conditioner for single rooms. In this air conditioner all the components, namely the compressor, condenser, expansion valve or coil, evaporator and cooling coil are enclosed in a single box. This unit is fitted in a slot made in the wall of the room.

2)     Split air conditioner: The split unit is comprised of two parts: the outdoor unit and the indoor unit. The outdoor unit, fitted outside the room, houses components like the compressor, condenser and expansion valve. The indoor unit comprises the evaporator or cooling coil and the cooling fan. Further, the present day split units have aesthetic looks and add to the beauty of the room. The split air conditioner can be used to cool one or two rooms.

                          

                                                                       

3)     Central air conditioning system: The central air conditioning system is used for cooling big buildings, houses, offices, entire hotels, gym, cinema hall, factory etc. If the whole building is to be air conditioned, HVAC engineers find that putting individual units in each of the rooms is very expensive initially as well in the long run. The central air conditioning system is comprised of a huge compressor that has the capacity to produce hundreds of tons of air conditioning. Cooling big halls, malls, huge spaces, galleries etc is usually feasible with central conditioning units only.

Central HVAC systems
While there are many different HVAC system designs and operational approaches to achieving proper system functionality, and every building is unique in its design and operation, HVAC systems generally share a few basic design elements:

• Outside air intake
• Air handling unit—a system of fans, heating and cooling coils, air-flow control dampers, air filters, etc.
• Air distribution system
• Air exhausts system.

Function

In general, outside (“supply”) air is drawn into a building’s HVAC system through the air intake by the air handling unit (AHU). Once in the system, supply air is filtered to remove particulate matter (mold, allergens, dust), heated or cooled, and then circulated throughout the building via the air distribution system, which is typically a system of supply ducts and registers.

In many buildings, the air distribution system also includes a return air system so that conditioned supply air is returned to the AHU (“return air”) where it is mixed with supply air, re-filtered, re-conditioned, and re-circulated throughout the building. This is usually accomplished by drawing air from the occupied space and returning it to the AHU by ducted returns, wherein air is collected from each room or zone using return air devices in the ceiling or walls that are directly connected by ductwork to the air-handling unit; Finally, some portion of the air within is exhausted from the building. The air exhaust system might be directly connected to the AHU and/or may stand-alone.Because the central air conditioning unit is located outside the home, it offers a lower level of indoor noise than a free-standing air conditioning unit.

Electricity supply to the buildings

Mains Supply

Mains is the general-purpose alternating current (AC) electric power supply. Worldwide, many different mains power systems are found for the operation of household and light commercial electrical appliances and lighting. The different systems are primarily characterized by their

• Voltage
• Frequency
• Plugs and sockets (a.k.a. receptacles or outlets)

In Sri Lanka, We use 230V/50Hz system.

Electrical distribution within the house

A consumer’s electrical installation begins at the connection of the meter. From the meter 230V supply is run to the consumer’s installation, which includes consumer’s unit and the necessary separate circuits for lighting, heating and power.

Consumer Unit

A consumers unit is one factory made unit consists of a switch for isolation (Main Switch), circuit breaking devices (fuses) and distribution of supply to the various circuits. An earthing connection block is fixed adjacent to the consumer’s unit.

Figure  – Consumer Unit

Isolation Main Switch

Isolation is the word used to describe the function of a device that effectively cuts off all voltages to the whole of an electrical installation. For a single face supply a double pole switch is included in the consumer’s unit for safety, to make a break in both the face in live and neutral conductors by the operation of manual switch.

Distribution

The three distribution conductors housed in the consumer’s unit are connected separately to the phase and neutral of the supply and to the earth conductor made through the earth connection block. From three distribution conductors the supply to each separate circuit is run from the face conductor through an over current protective device (fuse) and directly from the neutral and earth conductor to each circuit.

Main Earthing Terminal

This provides the necessary earth connection to the various circuit protective conductors, commonly called earth, to protect the installation against damage and danger of fire shock to persons.

Over current protective device

In the live conductor to each circuit cable run from the distribution conductor, is a fuse or circuit breaker as protection against current greater than that which the circuit can tolerate. The purpose of these devices is to cause a break in a circuit as protection against damage to conductors and insulation by overheating caused by excessive currents.  

 

Fuse

The fuse is a type of over current protection device. Its essential component is a metal wire or strip that melts when too much current flows, which breaks the circuit in which it is connected, thus protecting the circuit's other components from damage due to excessive current. The fuses are available in two types;

1.      Rewirable fuse

2.      Cartridge fuse

               Re-wirable fuse

This consists of a porcelain fuse holder through which the fuse wire is threaded and connected to the two brass terminals. The fuse is pushed in to position in the fuse block to make electrical contact. When the fuse wire has blown, the holder is pulled out, a new fuse wire fitted and the fuse pushed back in to place.

                 Cartridge fuse

   A cartridge fuse consists of a fuse wire in a tube with metal end caps to which the wire is connected. The fuse wire is surrounded by closely packed granular filler. When a circuit over current occurs the wire heats, ruptures and breaks the circuit, the energy released being absorbed by the granular filler without damage to the fuse carrier.

Miniature Circuit Breaker (MCB)

A circuit breaker is an automatically-operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow. Unlike a fuse, which operates once and then has to be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation.

Residual Current Circuit Breaker (RCCB)                     

A residual current device (RCD), similar to that of a residual current circuit breaker (RCCB) also popularly known as Earth Leakage Circuit Breaker (ELCB)., is an electrical wiring device that disconnects a circuit whenever it detects that the electric current is not balanced between the energized conductor and the return neutral conductor. Such an imbalance is sometimes caused by current leakage through the body of a person who is grounded and accidentally touching the energized part of the circuit. Poorly insulated equipment, faulty wires and incorrect use of an electrical device cause currents to flow through the wrong path (i.e., through the insulation) to the earth. A shock can result from these conditions. RCDs are designed to disconnect quickly enough to mitigate the harm caused by such shocks although they not intended to provide protection against overload or short-circuit conditions.                  

 Building wiring

In most countries, household power is single-phase electric power, with two or three wired contacts at each outlet.

• The live wire (also known as phase, hot or active contact), carries alternating current from the power grid to the household.
• The neutral wire completes the electrical circuit.
• The earth wire or ground connects cases of equipment to earth ground as a protection against insulation failures. Electromagnetic interference filters and surge protectors dispose of unwanted electric charges via the earth wire.

Various earthing systems are used to ensure that the ground and neutral wires have the correct voltages, to prevent shocks when touching grounded objects.Circuit breakers and fuses are used to detect short circuits between the live and neutral wires, or the drawing of more current than the wires are rated to handle to prevent overheating and fire. These protective devices are usually mounted in a central panel in a building.

Final Circuits

Final circuits are the circuits of a consumers installation that complete a circuit for the flow of current back to the supply neutral. Consumer’s unit will provide distribution terminals for the number of separate final circuits used.

Ring Circuit

The ring circuit makes a big loop or ring from one outlet to the next, round all the outlets and back to the consumer’s unit. Ring Circuits are commonly used for socket outlets that provide electrical supply to portable equipment such as vacuum cleaners, electric fires and kitchen equipments, through a socket outlet and a plug top.

  

A radial circuit is the name given to a circuit run through outlets  and which is not wired in the form of a ring but terminates at the last outlet. This arrangement is mainly used for lighting. In each radial circuit the phase conductor runs in the form of a loop from the circuit through a switch back to the light fitting that the switch control.

Plug and sockets

An electric plug is an electrical connector with contact prongs to connect mechanically and electrically to slots in the matching socket.

Wall sockets (power points, electrical outlets) are electrical connectors that have slots or holes which accept and deliver current to the prongs of inserted plugs. Sockets are designed to accept only matching plugs and reject all others. To reduce the risk of injury or death by electric shock, some plug and socket systems incorporate various safety features and design aspects.

                                   

Switch

A switch is an electrical component which can break an electrical circuit, interrupting the current or diverting it from one conductor to another. The most familiar form of switch is a manually operated electromechanical device with one or more sets of electrical contacts. Each set of contacts can be in one of two states: either 'closed' meaning the contacts are touching and electricity can flow between them, or 'open', meaning the contacts are separated and non-conducting.

Switches have been built in a wide range of sizes and types, from subminiature devices up to industrial plant switches that regulate megawatts of power on high voltage distribution lines.

Light Fixtures

A light fixture is an electrical device used to create artificial light or illumination. A wide variety of special light fixtures are created for use in the building construction industry.

Safety Requirements

For safety, the wiring requirements recommend good workmanship in the running of cables to avoid damage to insulation and conductors, and the making of connections and sound judgment in the selection of materials to prevent danger from shock to persons and the possibility of fires from overheating of conductors due to current overload by short circuit.

Short circuit

A short circuit is a fault in a circuit where a live conductor comes in to contact with another, by breakdown of insulation to provide a path of least resistance to flow with consequent greater current than allowed for in the circuit design. A short circuit may cause over heating of conductors and break down of insulation and so damage the insulation. It is to limit such occurrences that over current protective devices such as fuses and MCBs are fitted.

Earthing

The wiring regulations include regulations for protection against the dangers of electric shock to persons, damage to installations and the danger of fire from over currents and earth faults. The earth conductor on cables and the earthing connections to conductive metals provide an alternative path for unplanned flows of electrical energy.