ELECTRICAL SERVICES

ELECTRICITY :-- Electricity is a general term that encompasses a variety of phenomena resulting from the presence and flow of electric charge .

Electrical distribution and protection equipments :--

1. Fuses :-

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-conducting and non-combustible housing.

Protect electrical devices and components from overcurrent and short circuits that occur during inproperly operating circuits.

When fault current reaches a predetermined magnitude for a fixed period of time,current flow is interrupted through melting of an internal element.

Performance rating include voltage rating, current rating, rated breaking capacity.

Performance characterstic : Fast acting and time lag.

The fuse element is made of zinc, copper, silver, aluminum, or alloys to provide stable and predictable characteristics.

Fuse Types :-

1. Miniature fuse :- Commonly available in dimensions of

5 x 20 mm and 6.3 X 32 mm

2. Sub-miniature or micro :-

Compact circuit board layout.

Mainly 13-32 inch diameter fuses.

3. Automotive Fuse :-

Automotive fuses are a class of fuses used to protect the wiring and electrical equipment for vehicles. They are generally rated for circuits no higher than 24 volts direct current, but some types are rated for 42-volt electrical systems. They are occasionally used in non-automotive electrical products.

4. Blade Type Fuses :-

Plug-in fuses (also called blade or spade fuses), with a plastic body and two prongs that fit into sockets, are mostly used in automobiles .

Used in low voltage and high current applications.

Type Dimensions L x W x H Ampere ratings

Mini 10.9 x 3.6 x 16.3 mm2A, 3A, 4A, 5A, 7.5A, 10A, 15A, 20A, 25A, 30A

Low-Profile Mini 10.9 x 3.81 x 8.73 mm2A, 3A, 4A, 5A, 7.5A, 10A, 15A, 20A, 25A, 30A

Regular 19.1 x 5.1 x 18.5 mm1A, 2A, 3A, 4A, 5A, 7.5A, 10A, 15A, 20A, 25A, 30A, 35A, 40A

Maxi 29.2 x 8.5 x 34.3 mm20A, 30A, 40A, 50A, 60A, 70A, 80A, 100A

FUSE HOLDER :- Fuse holder are devices for containing,protecting and mounting fuses.

1. Open fuse holder :- Open fuse holder types are fuse claps,

fuse blocks, socket and plug on cap varieties.

2. Fully enclosed :- Fully enclosed variety may use a fuse carrier that is inserted into a holder or have other means to fully enclosed the fuse.

Circuit Breaker :- Circuit breaker are switching device capable of making, carrying and breaking current under normal circuit conditions and making, carrying for a specific time, and breaking current under specified conditions such as a short circuit.

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.

Actuator lever - used to manually trip and reset the circuit breaker. Also indicates the status of the circuit breaker (On or Off/tripped).

Actuator mechanism - forces the contacts together or apart.

Contacts - Allow current when touching and break the current when moved apart.

Terminals

Bimetallic strip

Calibration screw - allows the manufacturer to precisely adjust the trip current of the device after assembly.

Solenoid

Arc divider / extinguisher

Circuit Breaker

TyPES OF CIRCUIT BREAKER :-

Low voltage circuit breaker:--

1. MCB [miniature circuit breaker]:- rate current more than 100 A.

Trip characterstic normally not adjustable. Thermal or thermal – magnetic operation.

2. MccB [molded case circuit breaker] :- rated curent up to 1000 A. Thermal or thermal magnitude operation. Trip current may be adjustable in large rating.

WIRES :- A wire is a single, usually cylindrical, string of metal. Wires are used to bear mechanical loads and to carry electricity and telecommunications signals. Wire is commonly formed by drawing the metal through a hole in a die or draw plate .

Classified based on material :-

Copper :- Very good conductor and is easy to mold and bend.

Most commonly used.

Reasonable Price.

ALUMINIUM :- Cheaper and easy to shape and bend,

A less conductive material.

Electrical safety is an issue.

Heating occurs.

ALLOYS :- An alloy made from aluminium and copper to take advantage of both.

SILVER WIRES :- Best conductor of electricity .

It is too expensive.

CLASSIFICATION BASED ON USE :-

1. Triplex Wire :- It is arial cable uses to fed the power pole.

Wire ties to the wires sticking out of the weather

head.

2. Main Feeder wires :- These wires are usually type THHN wire and rated for 125% of the load required. These are usually black insulated wires coming out of the service weather head.

Panel Feed Wires :- These wires are also type THHN like the main feeder . A typical 100 A servicewould have a THHN set of wires. They would then be rated at 125 A. This would protect the wires if the amperage was at full 100 A.

Non-metallic sheathed wire :- This wire commonly called Romax. Is a plastic coated wire that has either 2 or 3 conductors.

Single Strand wires :- when your home is piped you will have to have another type of wire. Single strand wire is insulated and many of these can be pulled into the same pipe.

Bus Bars :- An aluminium or copper conductor supported by insulators that interconnects the loads and the source of the electrical power in an electric power system.

1. Rigid bus bars :-Low,medium and high voltage.

Sulphur hexafluoride.

Switches :- Devices used to allow electrical current to flow. When closed and when opened,they prevent current flow.

Common Switch Types :-

Push button

Rocket Rock

Toggle

Dual line

Rotary

Keylock

Slide

Snap action

Reed

Wiring :- Electrical wiring in general refers to insulated conductors used to carry electricity, and associated devices.

Types of wiring :-

1 . Cleat Wiring:-Types of wiring to be adopted is depends upon various factors,duarability,safety,appearance,cost,consumers budget etc

This system uses insulated cables sub protected in porcelain cleats.

Recommended only for temporary installations.

Cleats are made in pairs having bottom and top halves.

initially top and bottom cleats are fixed according to the layout. Then the cable is drawn , tensioned and cleats are tightened by screw.

Types :- Having 1,2 or 3 grooms to receive 1,2, or 3 wires.

Advantages :-

Cleat wiring is one of the cheapest wiring.

More suitable for temporary installation

When not required the wiring could be dismanteled without damaging cables,cleats and accessories.

Disadvantages:-

Wiring is exposed chnces of fire are there.

Not appealing

Less durable

B.I.S recommendations for cleat wiring :-

Not employed for wiring on damp walls or ceiling unless precautions are adapted for affectively preventing dampness.

Class of cables :- vulcanised rubber insulated cables, pvc and poluthene insulated cables, insulated cables could be used without any further protection.

Cleats :- All cleats should consist of two parts a base piece and a cap. Cleats shall be fixed at a distace more than 60 cm apart and at regular intervals.Cleats shall be inserted either with varnished wood fillets or varnished wood clamps.

Fixing of cleats :- IN ordinary cases cleats shall be attached. Cleats shall be such that conductor distance shall not be less than 2 cmfor pressure upto 250 volts

Branch load :- 2.5 cm apart

Sub-mains :- 4 cm apart

Batten wiring :- Tough rubber sheathed or pvc sheathed cabled are suitable to sum on teak wood battens

Metal sheathed wires are used.

teakwood shall be seasond and wel finished from all sides. Shall not be less than 10 mm in thickness

battens shall be painted with vanish prior to erection.

Battens shall be fixed to wallas using wall plug or wooden plug not more than 75 cm

Cables are held on battens.

Link Clip :- use to family clipping the cables in position.

Link Clip :- use to family clipping the cables in position.

link clips are of two types.

made of tin or brass coated tin.

ADVANTAGES :- easy to install.

widely used for indoor installations.

DISADVANTAGES :- Wires are exposed more chances of damage.

Chances of spreading fire are more.

not much appealing.

Cassing caping wiring :- For low voltage installation.

cables like vulcanised rubber,insulated cables,plastic insulated cables are used and carried within the wood casing enclosure

Not to be used in un ventilated or dap places . Unless precautions are taken.

Material and pattern of casing :-

all casing shall be of fust glass, seasoned teak wood or any other approved hardwood.

all sides well varnished,both inside or outside shealed varnish.

Advantages :- Wires not fully enclosed ,less chances of damage.

chances of fire spreading are less

better asthetically appealing.

Disadvantages :-Expensive.

only used in dry places.

Conduit wiring :- conduit is defined as a tube or channel.

Tubular conduit is most commonly used installation.

Types of conduit :-

Rigit steel conduit.

rigid non-mettalic conduit.

Flexible steel conduit.

Flexible non mettalic conduit.

Surface conduit :- conduit shall be finished with galvanised or stone surface.

Conduit accesories shall be threaded type and conduit shall be fixed using screwed couplers and accessories at a distance not more than 1 m and 30 cm in case of bends.

Diameter not less than 16 cm

For long runs : use inspection type couplers.

Advantages :- Fire protection

Water Proof

easy replacement of defective wires.

Disadvantages :- Expensive wiring

mostly used in factories only.