UNIT-VI

ELECTRICAL INSTALLATIONS AND SAFETY PROCEDURES

COMPONENTS OF SWITCH GEAR:

The apparatus used for switching, controlling and protecting the electrical circuits and

equipment is known as switchgear.

The term ‘switchgear’ is a term related with a wide range of products like circuit

breakers, switches, switch fuse units, earth leakage circuit breakers (ELCBs), etc...

A switchgear essentially consists of switching and protecting devices such as switches,

fuses, isolators, circuit breakers, relays, control panels, lightning arrestors, current

transformers, potential transformers, and various associated equipments.

FUSE :

A fuse is a short piece of wire or thin strip which melts when excessive current flows

through sufficient time. whenever the current flowing through fuse element increases

beyond its rated capacity then short circuit or overload occurs. This raises the

temperature and the fuse element melts, disconnecting the circuit is protected by it.

SWITCH FUSE UNIT (SFU):

It is Switched Fuse Unit. It has one switch unit and one fuse unit.

When we operate the breaker, the contacts will get close through switch and then the

supply will passes through the fuse unit to the output.

Whereas in Fuse Switch Unit there is no separate switch and fuse unit. There is only fuse

unit which act itself as a switch.

MCB(miniature circuit breaker):

MCB is an electromechanical device which guards an electrical circuit which

automatically switches off electrical circuit during abnormal condition of the network

means in over load condition as well as faulty condition. Nowadays we use an MCB in

low voltage electrical network instead of fuse. The fuse may not sense it but the miniature

circuit breaker does it in a more reliable way. MCB is much more sensitive to over

current than fuse.

Handling a MCB is electrically safer than a fuse. Quick restoration of supply is possible

in case of fuse as because fuses must be re- wireable or replaced for restoring the supply.

Restoration is easily possible by just switching it ON.

The normal current rating is ranges from 0.5-63 A with a symmetrical short circuit

breaking capacity of 3-10 KA, at a voltage level of 230 or 440V.

Characteristics of MCB

The characteristics of an MCB mainly include the following

Rated current is not more than 100 amperes

Normally, trip characteristics are not adjustable

Thermal magnetic operation

Earth Leakage Circuit Breaker (ELCB)

Early earth leakage circuit breakers are voltage detecting devices, which are now switched by

current sensing devices (RCD/RCCB). Generally, the current sensing devices termed as RCCB

and voltage detecting devices named as Earth Leakage Circuit Breaker (ELCB).

An ECLB is one kind of safety device used with high earth impedance to avoid shock.

These devices identify small voltages of the electrical device on the metal enclosures and

isolate the circuit if a dangerous voltage is identified. The main purpose of Earth leakage circuit

breaker (ECLB) is to stop damage to humans & animals due to electric shock.

If ample voltage seems across the ELCB’s sense coil, it will turn off the power, and

remain off until manually rearrange. A voltage sensing ELCB doesn’t detect fault currents from

human or animal to the earth.

Types of Earth Leakage Circuit Breaker (ELCB)

There are two types of Earth Leakage Circuit Breaker (ELCB)

Voltage Operated ELCB

Current Operated ELCB

Characteristics of ELCB

This circuit breaker connects the phase, earth wire and neutral

The working of this circuit breaker depends on current leakage

MCCB(Molded case circuit breakers):

Molded case circuit breakers are a type of electrical protection device that is commonly used

when load currents exceed the capabilities of miniature circuit breakers. They are also used in

applications of any current rating that require adjustable trip settings, which are not available in

plug-in circuit breakers and MCBs.

A molded case circuit breaker, abbreviated MCCB, is a type of electrical protection

device that can be used for a wide range of voltages, and frequencies of both 50 Hz and 60 Hz.

MCCBs tend to be much larger than MCBs. As with most types of circuit breakers, an MCCB

has three main functions:

1) Protection against overload – currents above the rated value

2) Protection against electrical faults – During a fault such as a short circuit or line fault, there

are extremely high currents that must be interrupted immediately.

3)Switching a circuit on and off – This is a less common function of circuit breakers.

MCCBs are available with current ratings that range from low values such as 15 amperes, to

industrial ratings such as 2,500 amperes. This allows them to be used in both low-power and

high-power applications.

Types of wires and cables:

Wire is a single electrical conductor, whereas a cable is a group of wires swathed

in sheathing.

The main requirements of the insulting materials used for cable are:

1. High insulation resistance.

2. High dielectric strength.

3. Good mechanical properties i.e. tenacity and elasticity.

4. It should not be affected by chemicals around it.

5. It should be non-hygroscopic because the dielectric strength of any material goes very much

down with moisture connect.

TPES OF CABLES

A brief description of the various cables used in domestic wiring is given here.

Rubber in its natural form is highly insulating but it absorbs moisture readily and gets

oxidized into a resinous material; thereby it loses insulating properties. When it is mixed with

sulphur alongwith other carefully chosen ingredients and is subjected to a particular tempera-ture

it changes into vulcanized rubber which does not absorb moisture and has better insulating

properties than even the pure rubber. It is elastic and resilient.

The electrical properties expected of rubber insulation are high break-down strength and

high insulation resistance. In fact the insulation strength of the vulcanized rubber is so good that

for lower voltages the radial thickness is limited due to mechanical consideration.

The physical properties expected of rubber insulation are that the cable should withstand

normal hazards of installation and it should give trouble-free service.

Vulcanized rubber insulated cables are used for wiringof houses, building and factories

for low power work.

PVC (Polyvinyl chloride) cables.

These are thermoplastic insulating materials and not used for high temperature as it gets

softened and flows down to heat. These are therefore, not used for heating appliances. PVC is

harder than rubber, hence a thin layer of PVC insulation is good enough. In fact, its thickness is

decided by mechanical reasons rather than electrical. The PVC insulated cables are lesser in

diameter as compared to TRS and more number of wires can be placed in conduit as compared to

TRS wires. These are used upto 1.1 kV voltages especially in concealed wiring system.

Tough Rubber Sheathed (TRS) or Cab Type Sheathed (CTS) Cables.

This cable is used where humidity is high and it does not deteriorate even during long

duration of exposure to moisture. As the name suggests these cables are provided with outer

protective covering of tough rubber over normal insulation. These are available as single, twin

and three cores with an earth continuity conductor. These are used on 250/500 volt circuits.

Earthing

Definition: The process of transferring the immediate discharge of the electrical energy

directly to the earth by the help of the low resistance wire is known as the electrical earthing.

The electrical earthing is done by connecting the non-current carrying part of the equipment or

neutral of supply system to the ground.

Mostly, the galvanised iron is used for the earthing. The earthing provides the simple

path to the leakage current. The shortcircuit current of the equipment passes to the earth which

has zero potential. Thus, protects the system and equipment from damage.

In almost every electrical installation made, earthing is used. The earthing system, also known as

the grounding system.

Importance of Earthing or advantages of earthing:

The earthing is essential because of the following reasons

The earthing protects the personnel from the shortcircuit current.

The earthing provides the easiest path to the flow of shortcircuit current even after the failure of

the insulation.

The earthing protects the apparatus and personnel from the high voltage surges and lightning

discharge.

Types of Electrical Earthing

The electrical equipment mainly consists of two non-current carrying parts. These parts are

neutral of the system or frame of the electrical equipment. From the earthing of these two non-

current carrying parts of the electrical system earthing can be classified into two types.

Neutral Earthing

Equipment Earthing.

Neutral Earthing

In neutral earthing, the neutral of the system is directly connected to earth by the help of the GI

wire. The neutral earthing is also called the system earthing. Such type of earthing is mostly

provided to the system which has star winding. For example, the neutral earthing is provided in

the generator, transformer, motor etc.

Equipment Earthing

Such type of earthing is provided to the electrical equipment. The non-current carrying part of

the equipment like their metallic frame is connected to the earth by the help of the conducting

wire. If any fault occurs in the apparatus, the short-circuit current to pass the earth by the help of

wire. Thus, protect the system from damage.

Factors Affecting Earthing Installations

Several factors can play a role in the earthing installations. The kind of soil is important for

determining the effectiveness of the earthing. The earth’s resistance, moisture level in the soil,

salts in the soil, etc. will play a significant role in determining the way the earthing is made. The

soil composition is also another factor that needs to be taken into consideration. For e.g., rocky

soil has to be treated very differently to wet soil.

Electric shock

An electric shock happens when an electric current passes through your body. This can burn both

internal and external tissue and cause organ damage.

A range of things can cause an electric shock, including:

power lines

lightning

electric machinery

household appliances

electrical outlets

Aside from the source of the shock, several other factors affect how serious an electric shock is,

including:

voltage

length of time in contact with the source

overall health

electricity’s path through your body

type of current (an alternating current is often more harmful than a direct current because it

causes muscle spasms that make it harder to drop the source of electricity)

symptoms of an electric shock

The symptoms of an electric shock depend on how severe it is.

Potential symptoms of an electric shock include:

loss of consciousness

muscle spasms(muscle contraction)

numbness (timmiri)

breathing problems

headache

problems with vision or hearing

burns

irregular heartbeat

First Aid:

If you receive an electric shock, it might be difficult for you to do anything. But try to start with

the following if you think you’ve been severely shocked:

Let go of the electric source as soon as you can.

If you can, call 911 or local emergency services. If you can’t, ask for someone else around

you to call.

If the shock feels minor ,See a doctor as soon as you can, even if you don’t have any

noticeable symptoms. Remember, some internal injuries are hard to detect at first.

In the meantime, cover any burns with sterile gauze(శుభ్రమైన గాజుగుడ్డ). Don’t use

adhesive bandages or anything else that might stick to the burn.

If someone else has been shocked

If someone else receives a shock, keep several things in mind to both help them and keep

yourself safe:

Don’t touch someone who has been shocked if they’re still in contact with the source of

electricity.

Turn off the flow of electricity if possible. If you can’t, move the source of electricity away

from the person using a non-conducting object. Wood and rubber are both good options. Just

make sure you don’t use anything that’s wet or metal based.

Stay at least 20 feet away if they’ve been shocked by high-voltage power lines that are still

on.

Call 911 or local emergency services if the person was struck by lightning or if they came into

contact with high-voltage electricity, such as power lines or if the person has trouble

breathing, loses consciousness, has seizures, has muscle pain or numbness, or is feeling

symptoms of a heart issue, including a fast heartbeat.

Check the person’s breathing and pulse. If the person is showing signs of shock, such as

vomiting or becoming faint or very pale, elevate their legs and feet slightly, unless this causes

too much pain.

Cover burns with sterile gauze if you can. Don’t use Band-Aids or anything else that might

stick to the burn.

Keep the person warm.

Treatment for electric shock

Even if the injuries seem minor, it’s crucial to see a doctor after an electric shock to check for

internal injuries.

Depending on the injuries, potential electric shock treatments include:

burn treatment, including the application of antibiotic ointment and sterile dressings

pain medication

For severe shocks, a doctor may recommend staying in the hospital for a day or two so they

can monitor you for any heart issues or severe injuries.

Types of batteries

Cells and Batteries:

A device which is used as a source of e.m.f. and which works on the principle of conversion of

chemical energy into electrical energy is called a cell.

But practically the voltage of a single cell is not sufficient to use in any practical application.

Hence various cells are connected in series or parallel to obtain the required voltage level. The

combination of various cells, to obtain the desired voltage level is called a battery.

Types of Cells

The two types of cells are,

1, Primary Cells: The chemical action in such cells is not reversible and hence the entire

cell is required to be replaced by a new one if the cell is down. The primary cells can

produce only a limited amount of energy. Mostly the non electrolytes are used for the

primary cells. The various examples of primary cells are zinc-carbon dry cell, zinc

chloride cell, alkaline cells, mercury cell etc.

2 Secondary Cells: The chemical action in such cells is reversible. Thus if cell is down, it

can be charged to regain its original stale, by using one of the charging methods. Such

cells, the electrical energy is stored in the form of chemical energy and the secondary

cells are also called storage cells, accumulators or rechargeable cells. The various types

of secondary cells are Lead-acid cell. Nickel-cadmium alkaline cell etc.

Primary cells

(1) Dry Zinc-Carbon Cell

(2)Mercury Cell

Secondary Cells

(1)Lead Acid Battery

Characteristics:

(2)Alkaline Cells

(i)Nickel-iron cell

(ii)Nickel – cadmium cell

Battery backup

A battery backup device is an electronic device that supplies secondary power in the absence of

main power, such as during a power outage. The battery backup will supply power when it

detects an outage.

Battery backup devices can also protect electronic hardware from power spikes,

dirty electricity and power outages.

They make battery backup devices in all sizes and power capacities, and depending on what

devices you are looking to protect, this will affect the size and capacities you will require.

unit 6

Elementary calculations of Energy consumption calculations

STEP I : Calculate Watts Per Day

In this step, simply multiply your device’s wattage by the number of hours you use it in a day. This will give you the number of watt-hours consumed each day.

For example, say you use a 125-watt television for three hours per day. By multiplying the watts (125) by the hours used (3), we find that the

television is consuming 375 watt-hours per day.

125 watts X 3 hours =

375 watt-hours per day

STEP II : Convert Watt-Hours to Kilowatts

Electricity is measured in kilowatt-hours on your bill, not watt-hours. One kilowatt is equal to 1,000 watts.

so to calculate how many kWh a device uses, divide the watt-hours from the previous step by 1,000. Using our previous example, this means you would divide 375 watt-hours by 1,000, resulting in 0.375 kWh.

375 watt-hours per day / 1000 =0.375 kWh per day

STEP III : Find Your Usage Over a Month

Now that you know the kWh used per day, multiply that by 30 to find your approximate usage for the month.

So, if your daily usage is 0.375 kWh, your monthly usage would be 11.25 kWh.

375 watt-hours per day X 30 days =

11.25 kWh per month

For refrigerator, for instance, runs 24 hours a day. Most refrigerators

consume anywhere between 300 to 780 watts of electricity. Let’s say your

model only uses 300 watts.

300 watts X 24 hours = 7,200 watt-hours per day

7,200 watt-hours per day / 1000 = 7.2 kWh per day

7.2 kWh per day X 30 days = 216 kWh per month

216 kWh per month x ₹3 per kWh = 648 per month

STEP III : Find Your Usage Over a Month

Now that you know the kWh used per day, multiply that by 30 to find your approximate usage for the month.

So, if your daily usage is 0.375 kWh,

your monthly usage would be 11.25 kWh.

375 watt-hours per day X 30 days =

11.25 kWh per month