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UNIT-5

ELECTRICAL INSTALLATIONS

SARDAR VALLABHBHAI PATEL EDUCATION SOCIETY MANAGED

R. N. G. PATEL INSTITUTE OF TECHNOLOGY (RNGPIT)

(FORMERLY KNOWN AS FETR)

ISROLI-TAJPORE-BARDOLI.

PROF. KEVIN C. SHAH

ASSISTANT PROFESSOR,

ELECTRICAL ENGG. DEPT.,

9825367016

kcshah@rngpit.ac.in

ELECTRICAL CIRCUIT

PREPARED BY: MR. KEVIN C. SHAH

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PREPARED BY: MR. KEVIN C. SHAH

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** A fuse consists of a metal strip or wire fuse element, of small cross-section compared to the circuit conductors, mounted between a pair of electrical terminals, and (usually) enclosed by a non-combustible housing.

** The fuse is arranged in series to carry all the current passing through the protected circuit. The resistance of the element generates heat due to the current flow.

1 FUSE

DIFFERENT TYPES OF PROTECTIVE DEVICE

PREPARED BY: MR. KEVIN C. SHAH

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**HRC fuse link is a very common, simple and effective electrical protection device against over load and short circuit current. It is so simple device that even an un-skilled person can handle it.

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**The HRC (high rupturing capacity) fuse−links are used to protect transformers, capacitor banks, and cable and overhead lines against short−circuits.

2 HRC FUSE

PREPARED BY: MR. KEVIN C. SHAH

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• A miniature circuit breaker (MCB) is an electromechanical device which operates and disconnects the circuit when the current reaches a pre- determined value.
• To secure our household appliances to heavy electrical short circuit and overload current, MCB is used.

3 MINIATURE CIRCUIT BREAKER (MCB)

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PRINCIPLE OF OPERATION :

• MCB is a device which operate on the two principles for the protection against overload and short circuit.
• Thermal for normal overload protection.
• Magnetic for short circuit protection.
• The thermal operation is achieved by bimetallic strip, which deflects when heated by any over current flowing through it.
• In doing so releases the latch mechanism and causes the contacts to open. It possesses inverse time-current, characteristics i.e. greater the current shorter the time required to operate the MCB.

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• When the short circuit occurs, the rising current energizes the solenoid operating plunger to strike the trip level causing immediate release of the latch mechanism.

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• Rapidity of the magnetic solenoid operation causes instantaneous opening of contacts.

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• APPLICATION OF MCB :
• MCBs are required in homes, offices, shops distribution boards .

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• ADVANTAGES OF MCB :
• Easily identify the fault zone of an electrical circuit.
• Simple to resume supply.
• Electrically safer.
• More sensitive to current than the fuse.
• Less maintenance and replacement cost.

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• DISADVANTAGES OF MCB :
• Only disadvantage over fuse is, this device is costlier.

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** It is same as that of MCB. Its rated current is up to 2500 A. It is characterized in low voltage circuit breakers.

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Its operation is Thermal or thermal-magnetic operation. Its trip current may be adjustable in larger ratings.

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Low voltage power circuit breakers can be mounted in multi-tiers in low-voltage switchboards or switchgear cabinets.

4 MCCB (MOLDED CASE CIRCUIT BREAKER)

PREPARED BY: MR. KEVIN C. SHAH

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There are two types of ELCB’S:

1. Voltage earth leakage circuit breaker (Voltage ELCB)

2. Residual current circuit breaker (RCCB)

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5 EARTH LEAKAGE CIRCUIT BREAKER (ELCB)

PREPARED BY: MR. KEVIN C. SHAH

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1. Voltage earth leakage circuit breaker (Voltage ELCB)

Voltage-ELCB is a voltage operated circuit breaker. The device will function when the Current passes through the ELCB.

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2. Residual current circuit breaker (RCCB)

**Current-operated ELCBs are generally known as Residual-current Circuit Breaker devices (RCCB). These also protect against earth leakage.

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**Both circuit conductors (supply and return) are run through a sensing coil; any imbalance of the currents means the magnetic field does not perfectly cancel. The device detects the imbalance and trips the contact.

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1. Wires

TYPES OF WIRES AND CABLES

a) SINGLE CORE WIRE:

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• This is the one solid/flexible wire with a P.V.C. coating available in a wide variety of colors.

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• It is used for connection which will not be disturbed, for example links between points of a circuit board or a switch board.

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b) MULTI CORE WIRE:

• Multi core cables are the cables, having more than one core with insulating layer on the conducting wire of copper or aluminum.

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C ) STRANDED WIRE:

•  This types of wire consists of many fine strand of wire covered by another PVC coating or insulating material.
• It is flexible and can withstand repeated bending without breaking.
• It is used for wide range of connections in house as well as in industries.
• Single strand wire has only one conductor covered by the insulator. This type of wire can carry low current through it.
• A multi strand wire has more than one conductor in form of a group, covered by the insulator.
• It has higher current capacity than single core wire.

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2. Cables

Construction of Power Cable

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Main parts are as follows:

1. Core or Conductor
2. Insulation
3. Metallic sheath
4. Bedding
5. Armouring
6. Serving

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1. Core or Conductor:

• A cable may have one or more than one core (conductor) depending upon the type of service for which it is intended.
• For instance, the 3-conductor cable shown in Figure is used for 3-phase service.
• The conductors are made of tinned copper or aluminium and are usually stranded in order to provide flexibility to the cable.  

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2.Insulation:

• Each core or conductor is provided with a suitable thickness of insulation, the thickness of layer depending upon the voltage to be withstood by the cable.
• The commonly used materials for insulation are impregnated paper, varnished cambric or rubber mineral compound.

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3.Metallic sheath:

• In order to protect the cable from moisture, gases or other damaging liquids (acids or alkalies) in the soil and atmosphere, a metallic sheath of lead or aluminum is provided over the insulation as shown in Figure.

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4. Bedding:

• Over the metallic sheath is applied a layer of bedding which consists of a fibrous material like jute or hessian tape.
• The purpose of bedding is to protect the metallic sheath against corrosion and from mechanical injury due to armouring. 

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5. Armouring:

• Over the bedding armouring is provided which consist of one or two layers of galvanized steel wire or steel tape.
• Its purpose is to protect the cable from mechanical injuries while laying it or handling it.
• Armouring may not be done in the case of some cables.

6. Serving:

• In order to protect armouring from atmospheric conditions, a layer of fibrous material like jute similar to bedding is provided over the armouring. This is known as serving.

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Armouring and serving are only applied to the cables for the

protection of conductor insulation and to protect metallic sheath from mechanical injury.

TYPES OF WIRING SYSTEMS

• Wooden casing and capping wiring
• Cab tyre sheathed wire
• Cleat wiring
• Metal sheathed wire
• Conduit wiring

WOODEN CASING AND CAPING WIRING

• In this system of wiring, the conductor used is either V.I.R or P.V.C. cable.
• The casing is fixed on the wall with the help of wooden screws and gutties already cemented in the wall.
• The casing is usually placed 3 to 3.5mm apart from the wall.
• The capping is screwed to the casing by means of wooden screws fixed at every 15cm on the center fillet.
• This type of wiring should be adoped only for voltages up to 250V in dry places and in places where there is no risk of fire.

• ADVANTAGES

1. It is easy to install and repair.
2. Conductor are strongly insulated.
3. Capping provides protection against mechanical injury.
4. It gives better appearance than cleat wiring.
5. Its cost is quite low as compared to other systems of wiring except cleat wiring.
1. DISADVANTAGES
1. It is not suitable in damp situation.
2. There is risk of fire.
3. This type of wiring can be used only on surface and cannot be concealed in plaster.
4. To make the job good looking, highly skilled labour is required. Hence labour cost more.

CAB TYRE SHEATHED WIRE

• This type of wiring is also used for house wiring and is quite cheap.
• C.T.S. or T.R.S. conductors are employed.
• The wires are run on the teak wooden buttons which are fixed on the wall.
• their thickness should not be less than 10mm and their width will depend upon the number of conducting wires to be run over this batten.
• C.T.S or T.R.S Cables are used for this type of wiring are not much affected by chemicals, water or steam, they are affected by lubricating oil.
• This type of wiring has long life, better appearance, less risk against fire.

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• ADVANTAGES

1. It is easy to instal and repair.
2. It is fire proof upto a certain limit.
3. It is cheaper than other types of wiring except cleat wiring.
4. The conductors have strong insulation therefore it has longer life.
5. Chemicals do not affect the conductors installation.
1. DISADVANTAGES
1. The conductors are open and liable to mechanical injury,therefore,this type of wiring cannot be used in workshop,etc.
2. Its use in places open to sun and rain is restricted.
3. Good workmanship is required to make a sound job in TRS wiring.

CLEAT WIRING

• This wiring is normally used for temporary wiring purpose. such as for functions, marriages etc.
• In this type wiring vulcanized Indian rubber or polyvinyl chloride insulated wires are used as conductors.
• wires are held to the walls and ceilings with the help of porcelain or plastic cleats which are placed 6mm off the walls.
• Grooves are provided in the base portion of the cleat for accommodation of the wires.
• It can be completed quickly and the wiring materials can be recovered easily while dismentling.
• Cleat wiring is not permitted in damp places and also for permanent job.

• ADVANTAGES

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1. A little skill is required to lay the wiring.
2. This wiring can be installed very quickly.
3. It is the most suitable for temporary wiring.
4. Inspection, alteration and additions can be made easily.
5. The wiring can be dismelted very quickly and whole of the material is recover.
6. It is cheapest system of wiring.
1. DISADVANTAGES
1. It gives a rubish look.
2. It is rarely employed for permanent jobs.
3. Oil and smoke are also injurious to V.I.R.
4. Mechanical injuries may damage the conductor since there is no protecting cover.

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METAL SHEATED WIRING

• This system of wiring is similar to C.T.S. Wiring.
• Only difference is that ,V.I.R.conductors covered with lead alloy sheath are used.
• The metal sheathed cables are run on the wooden batten. the batten is fixed on the wall by means of screws and gutties already cemented into the wall.
• This type wiring is also adopted for low voltage installations.
• Protection against mechanical injury, dampness and atmospheric conditions is much better in this system compared to all the earlier system of wiring.
• This system of wiring can be used in damp places or in place exposed to sun and rain.

• ADVANTAGES

1. The conductors are protected against mechanical injury.
2. It has longer life.
3. Conductors are protected against chemicals.
4. It can be installed in open space.
5. It gives better appearance.
1. DISADVANTAGES
1. The metal sheathed cables are costlier than C.T.S. or T.R.S. wires.
2. In case of leakage, there is every risk of shock.
3. Skilled labour and proper supervision is required.
4. It is not suitable for places where chemical corrosion may occur.

CONDUIT WIRING

• Conduit wiring system is the best for domestic and commercial installations.
• Galvanized or zinc – conduit are used in exposed position, damp or humid atmosphere,etc.
• The size of conduit is stated as per its outer diameter and the standard size are 12,16,19,25,31,38,50 and63mm.
• Conduits are available in standard lengths of about 4m.
• Conduit is made of mid-steel, specially annealed so that it can be easily bent or set without breaking.
• The life of this installation is sufficiently long.
• Standard conduits are supplied with black enamel coating on its internal and external surface.
• modern practice is to conceal the conduit in the plaster of the wall, so that the appearance of the house or the building remains unaffected.

• ADVANTAGES

• Conduit provides protection against mechanical injury.
• Conduit provides protection against chemicals.
• Conductors are safely secured from moisture.
• It has longer life.
• The whole system is water proof.
• It is shock proof also if earthing and bonding is properly done.
• DISADVANTAGES
• It is very costly system of wiring.
• It requires more time for erection.
• It requires highly skilled labour.
• Internal condensation of moisture may cause damage to the insulation unless the system outlets are properly drained and ventilated.

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Why Earthing is important ?

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Earthing is important to ensure:

**Safety of personnel

**Safety of equipment

** The process of transferring the immediate discharge of the electrical energy directly to the earth by the help of low resistance wire is known as the electrical earthing.

**Prevent or at least minimize damage to equipment as a result of flow of heavy currents

**Improvement of the reliability of the power system.

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Pipe Type Earthing

In this method hot dip GI pipe of size 40 mm dia × 2.5 meter is being used for equipment earthing. This pipe is perforated at each interval of 100mm and is tapered at lower end. A clamped is welded with this pipe at 100 mm below the top for making connection with hot dip GI strip of size 40mm × 3mm of required length as per the site location up to the equipment earth / neutral connection. On its open end funnel is being fitted for watering purpose. The earth pipe is placed inside 2700 mm depth pit. A 600mm dia “farma“ of GI sheet or cement pipe in two halves is are placed around the pipe. Then the angular space between this “farma” and earth pipe is back filled with alternate layer of 300mm height with salt and charcoal. The remaining space outside “farma” will be backfilled by excavated earth. The “farma” is gradually lifted up as the backfilling up progresses. Thus the pit is being filled up to the 300mm below the ground level. This remaining portion is covered by constructing a small chamber of brick so that top open end of pipe and connection with main earth pipe will be accessible for attending when necessary. The chamber is closed by wooden/stone cover. Water is poured into the pipe through its open end funnel to keep the earthing resistance within specific limit.

Type of Earthing

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• Applications :
• It is mostly used for
• Residential areas.
• Commercial areas.

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• Advantages :
• Simple design.
• Easy to install in good soils.
• Hardware readily available.

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• Disadvantages :
• High impedance.
• Hard to install in rocky soil.

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Plate Type Earthing

• In this, cast Iron plate of size 60 cm × 60 cm × 6.35 mm thick plate is being used as earth plate. This is being connected with hot dip GI main earth strip of size 50mm breadth × 6mm thick × 2.5 meter long by means of nut, bolts and washers of required size. The main earth strip is connected with hot dip GI strip of size 40mm × 3mm of required length as per the site location up to the equipment earth / neutral connection. The earth plate is back filled and covered with earthing material (mixture of charcoal & salt) by 150mm from all six sides.

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• The remaining pit is back filled with excavated earth. Along with earth plate, rigid PVC pipe of 2.5 meter long is also provided in the earth pit for watering purpose for to keep the earthing resistance within specific limit.

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• Applications :
• It is mostly used for
• Industrial areas.
• Generators.
• UPS.
• Transformers.
• Advantages :
• Can achieve low resistance contact in limited area.
• Easy to install good soils.
• High Efficiency.

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• Disadvantages :
• Most difficult to install.
• Should be installed vertically.

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