Electric work 02 -Electrical cables and fittings

Electrical cables 

Electrical cables are used to transmit electricity, and they are made up of two or more wires bonded together (through twisting or braiding). These wires are covered by protective and insulating material. There are many different types of electrical cables, and they are typically categorized depending on such factors as electrical conductivity, type of insulation, type of protector (or covering), weight, cost, and specific uses.


Other factors that determine the type of electrical cables include voltage rating, type of protective covering, fiber core size, cable weight and cable diameter.

• A cable is an assembly of one or more conductors (wires) with some flexibility.
• A lead is a complete assembly of cable and connectors.
• A wire is a single conductor which may have an outer layer of insulation (usually plastic).

Types of cables

• Single and multi-strand conductors

Solid wire, also called solid-core or single-strand wire, consists of one piece of metal wire. 

        Multi-strand wire                                                                Single –strand wire

Stranded wire or multi strand conductor is composed of a bundle wires to make a larger conductor.

Stranded wire is more flexible than solid wire of the same total cross-sectional area. Solid wire is cheaper to manufacture than stranded wire and is used where there is little need for flexibility in the wire. Solid wire also provides mechanical ruggedness; and because it has relatively less surface area which is exposed to attack by corrosives, protection against the environment. 

Stranded wire is used when higher resistance to metal fatigue is required. Such situations include connections between circuit boards in multi-printed-circuit-board devices, where the rigidity of solid wire would produce too much stress as a result of movement during assembly or servicing; A.C. line cords for appliances; musical instrument cables; computer mouse cables; welding electrode cables; control cables connecting moving machine parts; mining machine cables; trailing machine cables; and numerous others.

Single-cored and multi-cored cables

Single core

Single core cable is mostly used for industrial applications where it is run in conduits. In domestic wiring it is usually only used for certain situations such as for electric fittings. 

Multi Core

Colours used for the cable insulation 

Electrical wires have markings stamped or printed on the outside sheath of the cable. These markings tell what type and size of wire that you have. And also the color of the wires inside of the sheath reveals that different color wires serve different purposes.

Purpose	Colour
Protective earth (PE)	Green/yellow bi-colour
Neutral (N)	Blue
Single phase: Live (L) Three phase: L1	Brown
Three phase: L2	Black
Three phase: L3	Grey

Flexible cables colour code

No. of cores	Colours
2 core	Brown , Blue
3 core	Brown , Blue , Green and yellow
4 core	Brown , Blue , Green and yellow , Black or grey
5 core	Brown , Blue , Green and yellow , Black or grey , Black or grey

Basic types of electrical accessories used for domestic single phase circuits.

Mounting Box

Mounting boxes protect connections between two or more wires or between wires and switches or fixtures. Mounting boxes are available with different sizes and made of different materials such as ABS, plastic , PVC and etc…

Switches

An electrical switch controls the flow of power in an electrical circuit. It provides an open circuit in the off position and acts as a closed circuit in the on position.

Types of switches

·        

Single Pole Switches  

This is the simplest type of switch. Most residential switches are single pole switches.

	Single pole switch with neon indicator		Single pole switch without neon indicator

 

·       Double Pole Switches

 

These types of switches are often used to switch mains electricity because it can isolate both the live and neutral connections at once.

Socket outlet

Socket outlets are used when temporary electrical connections are required. eg : for connecting table lamp , table fan , radio ,etc……There are two types of socket outlets available in the market.

       I.            Two pin type (live, neutral)

    II.            Three pin type ( live , neutral and earth)

As all appliances connected by flexible leads should be earthed, two pin type is outdated today. The 3 pin type is standardized for domestic wiring and use at 2,5,13 and 15 A rating.

Ceiling rose

Ceiling rose is used to connect pendant lamps, ceiling fans and etc… to the supply system. Ceiling rose consist of two main parts called base and cover. Both the parts are made up of Bakelite or porcelain. Terminals are provided on the base and a hole is made in the cover to take out the flexible wire.

 

Junction box

Junction boxes are used in electrical installation to join some conductor and provide different paths for different conductors. Most of the junction boxes are made of plastic.

Cable clips

Cable clips are used to attach electrical cables to a wall or baseboard. Based on the cables that are used, suitable type of cable clips should be selected.

  

    

           

Read More

Electric work01 -Hand Tools

             
          Hand tools are the tools which are used by human in a workshop for various electrical installation related works and also for various maintenance works.







Types of hand tools

1. Screw driver
A hand tool used to fix and remove screws. Used in assembling work and maintenance work. Available in three main types:

a) Flat type – Point of the screw driver is flat shape used for straight slot screws.
b) Pozidriv type (Philips type) - Point of the screw driver is special shape (x shape) to match with             the slot in pozidriv slot screw. Used for Pozidriv slot screws.
c) Offset screw driver – Designed for use in confined areas where it is impossible to use a standard         screw driver.


2. Pliers

A hand tool, used to hold smaller components for various activities such filing, drilling etc. We can cut wires pulled out tighten small components by using pliers.

3. Hammer
A hand tool used for delivering blows (force) in chipping using chisel, bending, straightening and other operations. Hammers are forged from high carbon steel. Hammer sizes are specified by their weight. Main types of hammers are:

a) Ball pein hammer – Most commonly used hammer. Consists of flat face for general work and ball         pein for peining or riveting.
b) Cross pein hammer – Used for sheet metal forming
c) Straight pein hammer – Used for sheet metal work


4. Tape measure

 A tape measure is a portable measurement device used to quantify the size of an object or the distance between objects. The tape is marked along the tape edge in inches and fractional inches, typically in quarter-, eight-, and sixteenth-inch increments. Some tape measures are marked in millimeters, centimeters, and meters on one edge.
The most common tape measures are 12 feet, 25 feet, or 100 feet in length.


Portable power tools suitable for drilling walls

• Hand drilling machine
 Manually hand operated drilling machine. Used for rough and smaller diameter hole drilling.(Up to about 5mm dia.) Mostly used to drill soft materials.

• Portable electric Drilling machine 
 Electrically operated hand drill. Used for rough and small diameter hole drilling (up to about 18mm dia.)Spindle is driven by the electric motor and feeding of drill is done by human hand. Can drill metals also.

• Hammer drill

 A hammer drill has a specially designed clutch that allows it to not only spin the drill bit, but also to punch it in and out (along the axis of the bit). Hammer drills are more expensive and more bulky than regular drills, but are preferable for applications where the material to be drilled—concrete block or wood studs—is unknown. For example, an electrician would use a hammer drill for attaching items (such as an electrical box) to either wood studs (if used as a conventional power drill) or masonry walls (if used as a hammer drill).

Drill bit
The cutting tool used on a drilling machine is known as a Drill bit ( Drill). The most common type of drill is Twist Drill.
Twist drill
Twist drill is consists of 2 main parts:
i) Body – A cylindrical part make with 2 helical flutes to provide the cutting lips and cutting point to remove the chips. To  reduce the friction of the body and the point against the walls of the hole and for better guiding of the tool, only a part of the cylindrical surface is left project and form what are called the lands.
ii) Shank – The part of the drill which to the machine. Depend on the method of applied to securing the drill, the shank available as
a) Straight or Cylindrical type – Available as drills which are less than 12.7mm in diameter. When fixing the straight shank drills to a drilling machine a Drill chuck or a Collet chuck is used.
b) Taper Shank – Consists of standard Morse taper shank. Available as drills which are more than 12.7mm in diameter. When fixing the taper shank drills to a drilling machine the Morse tapered spindle hole or Morse tapered sleeve is used.


Types of twist drill

• General purpose drill – a drill with standard helix angle or Rake angle of 60°. Used to drill mild steel, cooper alloy etc.
• Slow helix drill – A drill with larger helix angle , Used to drill hard materials
• Quick helix angle - A drill with smaller helix angle , Used to drill  soft materials
• Straight flute drill – Flute which take straight shape. Used to drill very soft material
• Flat drill – A drill without a point. Used to drill sheet metal

Read More

Plumbing work02 -Basic Types of Pipe and Fittings

       
                  Pipes are used in water supply systems to deliver water from one place to another. Water flaws through pipes by:
Gravity or
Force pumping

For efficiency, pipes must deliver water with least friction. For this reason pipes are usually circular and the inner surface is made smooth. Man has used many materials for the manufacture of pipes. In the first instance bamboo trunks were used as pipes by boring through the nodes. Then pipes were made by twisting lead sheet around circular timber. Later hot drawn, cold drawn or seam welded pipes were manufactured from metals like copper, steel, stainless steel, aluminum and brass etc. In large water supply installations pipes made out of:-
Cast iron
Black iron
Concrete
Asbestos were used.

A major disadvantage of these pipes was that they are heavy and joining was complicated. During World War 2 the necessity for a more flexible and convenient pipe type was felt and the result was the synthetic polymer pipe.

Polymer Pipes - The advantages of polymer pipes are:
a) Easily moulded to any shape or size
b) Easy to work with and are light weight
c) High resistance to weathering and corrosion
d) Almost maintenance free
e) Good electrical, sound and heat insulation
f) Withstand moisture, oils and acids.

Plastics (polymers) are mainly divided into 02 groups:-

• Thermoplastics - which become soft on heating and returning back to its original form on cooling

• Thermosetting plastics - which undergo chemical changes on heating and do not return to original form on cooling

Polymer (plastic) pipes are a petroleum bi-product. Two main plastics are used in the manufacture of pipes namely:-
– PVC (Poly Vinyl Chloride)
– HDPE (High Density Polyethylene)

PVC is identified as a rigid pipe while HDPE is identified as a flexible pipe. Polymer pipes are manufactured by extrusion or moulding.

Pipe Fittings
Pipes cannot always be installed as straight runs. They need to:-
a) Change direction
b) Branch off
c) Reduce or enlarge in size
d) Connect to appliances

These need special pipe components which are named pipe fittings. There are various pipe fittings used for the different requirements and locations:
Bends (90˚ or oblique), Elbows, Reducers, Tees (equal/unequal), Sockets (Plain/valve/faucet), Union couplings

 

Union coupling                                               Elbow 

                            

Tee                                                                  Bend

‘Y’ junction

Valves and Taps (or faucets)

Valves and taps (faucets) are required in pipe systems to control flow. Flow control includes - Increase flow, Decrease flow, Stop flow or Open flow.

•      Different types of valves are used.

                     

Gate Valve                                                                          Bib Tap

             

Working mechanism – Bib tap                                                                      Globe valve

                  

Working mechanism – Globe valve                       Working mechanism – Gate valve

Read More