Electrical wiring and safety and protection

Course: Diploma

Subject: Basics of Electrical Engineering

Unit: V

Connectors and switches• An electrical connector is an electro-

mechanical device for joining electrical circuits as an interface using a mechanical assembly. Connectors consist of plugs (male-ended) and jacks (female-ended). The connection may be temporary, as for portable equipment, require a tool for assembly and removal, or serve as a permanent electrical joint between two wires or devices. An adapter can be used to effectively bring together dissimilar connectors.

Factors affecting electrical wiring

1.Durability:-Type of wiring selected for particular application must be sufficiently durable .It should fulfill the requirement of the consumer. It should be according to proper specification.

2.Safety:-As there is danger of loosing life in case of electric shocks, safety must be observed strictly.

3.Accessibility:-There should be certain prevision for future expansion.

4.Cost:-There must be proper balance between convenience and look of the wiring from installation cost point of view.

Cont..

5.Maintainance:-The maintainance cost of wiring should be as low as possible.There should be scope for further extension of wiring . Renewal of wiring should be easily possible.

Types of Wiring

1)Cleat wiring

2)CTS wiring or "FRS wiring or batten wiring

3)Metal sheathed wiring or lead sheathed wiring

4)Casing and capping

5)Conduit wiring

1)Cleat Wiring:• Introduction• The types of wiring to be adopted is dependent on

various factors, viz, durability, safety, appearance, cost, consumer's budget etc.

• Cleat Wiring• This System uses insulated Cables sub protected in

porcelain cleats.

Cont..

• Cleat wiring is recommended only for temporary installations. The cleats are made in pairs having bottom and top halves. The bottom half is grooved to receive the wire and the top half is for cable grip. Initially the bottom and top cleats are fixed on the wall loosely according to the layout. Then the cable is drawn, tensioned and the cleats are tightened by the screw. Cleats are of three types, having one, two or three grooves, so as to receive one, two or three wires. Two types of cleats.

Cont….

• Cleat wiring is one of the cheapest wiring considering the initial cost and labor, and is most suitable for temporary n :ring. This wiring can be quickly installed, easily inspected and altered. When not required, this wiring could be dismantled without damage to the cables, cleats and accessories.

Cont..

Fig 1

• Care should also be taken ensure that grooves f porcelain cleats are essential and the difference in size shall be reasonable. Care should also be taken ensure that grooves of porcelain cleats do not compress the insulation nor be too wide for a loose fit. Under no circumstances two wires shall be placed in one groove of the porcelain cleats.

• Batten Wiring

• Advantages:

I) Easy installation.

Materials can be retrieved for reuse.

Flexibility provided for inspection, modifications and expansion.

Relatively economical.

Skilled manpower not required.

Disadvantages:

Appearance is not good.

Open system of wiring requiring regular cleaning.

Higher risk of mechanical injury.•

• In this wiring symant. wires •harathed In tough nahlter are used which are quite nesIble. They are c. on wooden I eeeee ns with brass clips Oink or Jolts° and nays. on to Me walls or re iiiii us by nat hand saran.

• IS/T RS WIRING• h cables are moisture and chemical proof. 'I hey Sr., •ultahle

fur• damp ell 00000 but not •ullable for outdoor use In sunlight.lkS

wiring Is mailable for lighting In low voltage Installations.

Cont…

• Metal Sheathed or Lead Sheathed wiring: The wiring is similar to that of CTS but the conductors (two or three) are individually insulated and covered with a common outer lead-aluminum alloy sheath. The sheath protects the cable against dampness. atmospheric extremities and mechanical damages. The sheath is earthed at every junction to provide a path to ground for the leakage current. They are fixed by means of metal clips on wooden battens. The wiring system is very expensive. It is suitable for low voltage installations.

•

• Lead-sheathed electrical wiring in Pilot quarters

• Precautions to be taken during installation: The clips used to fix the cables on battens should not react with the sheath.

• Lead sheath should be properly earthed to prevent shocks due to leakage currents.

• Cables should not be run in damp places and in areas where chemicals (may react with the lead) are used.

• Advantages: Easy installation and is aesthetic in appearance.

• Highly durable.• Suitable in adverse climatic conditions provided the

joints arc not exposed.• Disadvantages:• Requires skilled labor-• 'Very expensive.• Unsuitable for- eilcolicfli industries.

• Casing and Capping:• It consists of insulated conductors laid inside rectangular,

teakwood or PVC boxes having grooves inside it. A rectangular strip of wood called capping having same width as that of casing is fixed over it. Both the casing and the capping are screwed together at every 15 crns- Casing is attached to the wall. Two or more wires of same polarity are drawn through different grooves- The system is suitable for indoor and domestic installations.

• Cheaper than lead sheathed and conduit wiring.

• Provides good isolation as the conductors are placed apart reducing the risk of short circuit.

• Easily accessible for inspection and repairs.• Since the wires are not exposed to atmosphere, insulation

is less affected by dust, dirt and climatic variations.

Domestic wiring system• Accessories required for domestic wiring:-

a)Wire and cable

b)Flexible cords

c)Switch:-They are classified in two types:-

I)Tumbler switch

II) Flush switches According to operation required they are classified as

One way switch Two way switch Centre off switch Double pole switch push button switch Table lamp switch Bed switch

Electricity

The main advantage of electrical energy is that it can be transported over large distances to our homes.

Wires carry electricity from power stations to our homes/schools/offices.

Electric Shocks

Electricity is dangerous and can kill!!

An electric shock can:

You can get an electric shock from anything which is plugged in or connected to the mains supply.

• Affect your muscles.

• Affect your nerves.

• Paralyse you.

• Stop your heart beating.

Electrical SafetyThe wires which carry electricity consist of two parts:

• The metal wires.

• The plastic coating round the metal wires.

Electrical Safety

The metal wires act as a conductor of electricity.

The plastic coating acts as an insulator which prevents people from being electrocuted.

Conductors are materials which allow electricity to pass through them easily.

Insulators are materials which do not allow electricity to pass through them easily.

The PlugElectrical cables allow you to:

• Plug appliances into the mains supply.

• Draw electricity from the mains supply.

The PlugMost electric cables normally contain three wires:

Each of these three wire have different colours of insulation.

• The live wire.

• The neutral wire.

• The earth wire.

The PlugYou have to remember the names and colours of each of these three wires. You also have to remember the position of each of these three wires in a standard plug.

Wire Insulation Colour

Location

LIVE BRown BR – bottom right

NEUTRAL BLue BL – bottom left

EARTH Green/Yellow Centre

Electrical Safety

Appliances have three safety devices:

• The fuse.

• The earth wire.

• The switch.

These devices are designed to stop you from being electrocuted and to prevent the appliance from being damaged.

The Fuse

A fuse is a thin piece of wire which will melt when too much current passes through it.

A 3A fuse will melt when the current is greater than 3A.

When a fuse has blown, the wire inside it has melted.

Current is a flow of electricity and is measured in amps (A).

Example

The Fuse

When the wire melts, all current is stopped from reaching the appliance and switches it off.

The fuse stops a large current from flowing through the appliance which could cause wires to overheat, melt or catch fire.

The SwitchTogether, the fuse and switch control the amount of electricity that enters an appliance.

The fuse and the switch are connected to the live wire.

Electricity comes in through the live wire.

If the fuse is blown, or the switch is off, then the electricity cannot reach the appliance.

What can go wrong!The most dangerous thing that can happen is that the live wire can become loose inside an appliance and touches the casing.

This makes the casing LIVE!

If you touch the LIVE casing, you could be electrocuted as you are providing a path for the electricity to flow.

PreventionTo prevent electrocution, the earth wire is connected to the casing of the appliance.

If the live wire touches the casing, the earth wire provides a path for the electricity to flow.

This blows the fuse and switches the appliance off, leaving you safe.

Fault SpottingFault What could happen!

bare wires showing Danger of electrocution.

live and neutral wiresreversed

The appliance will stillwork but when it isswitched off it can stillelectrocute you.

wrong fuse used The fuse will not blowwhen it should and there isa danger of overheatingand/or fire.

References-Images1.https://www.google.co.in/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&ved=0CAcQjRw&url=https%3A%2F%2Flaw.resource.org%2Fpub%2Fin%2Fbis%2FS05%2Fis.sp.30.2011.svg.html&ei=Q7SjVJfnLcqMuASS2oHYCQ&bvm=bv.82001339,d.c2E&psig=AFQjCNG0L1rrS9lF1F2U1T3lSNW4cPGkiQ&ust=1420101016860706