Electrical Installation Practice - Basics

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SAFETY

Installation of electrical equipment to fullfill a specific purpose is known as electrical installation.

In dealing with the electrical installation, it is necessary to ensure the safety of personnel as well as the

protection of equipment from electrical faults.

Types of faults in domestic systems are

(a) the short circuit faults (phase to neutral faults) – as a result of which large currents will flow and

damage may occur to wires, insulators, switches, etc., due to over heating; and

(b) insulation failure (fault between the phase conductor and non-current carrying metallic parts)

of an electrical equipment - as a result of which high voltages may appear on the frames of

equipment and may be dangerous to a person coming in contact with it.

Therefore, all electrical wiring systems and all electrical apparatus associated with wiring must be

protected against excess currents and earth leakage.

The most popular methods of protection are

(i) earthing or grounding of equipment

(ii) use of fuses or circuit breakers (such as the Miniature Circuit Breaker – MCB)

(iii) use of earth leakage and residual current circuit breakers. The earth leakage protectiondevice is commonly known as Trip Switch by electricians.

Electrical Injuries

Electrical shock

Electrocution (death due to severe electrical shock)

Burns (from an arc flash)

Falls (an electrical shock might cause you to lose your balance, pull back, jump, or fall off a

ladder)

Electric Shock If an electric current passes through the human body, the effects could be an electric shock or

even death. The degree of danger of electric shock depends on the value of the body current and the time

for which the current flows.

Zone 1 - No sensationZone 2 - Perceptibility

of current, but noharmful effect (10 mA

is the threshold of let-go)Zone 3 - Muscular

contractions anddifficulty in breathing.

Usually no danger of

ventricular fibrillation(0.5% probability)Zone 4 - Probability of ventricular fibrillation

increases a - up to 5%, b - up to 50%, c -greater than 50%



IEE Wiring Regulations/British Standard BS 7671Rules and regulations have been framed to ensure that all electrical installations provide adequate

degree of safety from fire and shock risks, to those who operate the installations and their associatedapparatus, equipment and machines. 16th Edition (1992) of IEE Wiring Regulations is used in Sri Lanka.

Following are some important information available in these regulations:

The Regulations are designed to protect persons, property and livestock from electric shock, fire, burnsand injury from mechanical movement of electrically actuated equipment.Prevention of electric shock is carried out by Insulation of live parts.

Safety requirement of IEE regulations

http://en.wikipedia.org/wiki/British_Standard






• Testing includes continuity of live, neutral and protective conductors, the resistance of earth

electrodes,

insulation resistance of all live conductors to earth, insulation resistance between live conductors,

polarity to ensure all switches are connected in phase conductors and not neutral; phase earth loop

impedance tests, operation of residual current devices.

The regulations are in seven parts as

Arrangement of the 16th Edition Parts

Part 1 - Scope, objects and fundamental requirements for safety

Part 2 - Definitions

Part 3 - Assessment of general characteristics

Part 4 - Protections for safety

Part 5 - Selection and erection of equipment

Part 6 - Special installation or locations – particular requirements

Part 7 - Inspection and testing

[514-06-03] is the third Regulation in the sixth group or subsection of Section 4 of Chapter 1 in Part 5



SYMBOLS: Cables, number of conductors and cable crossovers





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Electrical Installation Practice - Basics