INTRODUCTION:

Electricity has now become basic need of mankind.  Life without it cannot be imagined.  Inventions of various electrical gadgets have made life easy and beautiful. But at the same time electricity has to be handled with utmost care. Ignorance towards electrical safety has claimed many lives and loss of property.

It has been reported that more than 75% of fires take place due to short circuits in electrical installations. Many human beings have lost their lives due to electrocution. As per the National Crime Record Bureau statistics for the year 2015 a total of 10,200 number of electrocution cases with 364 and 9986 persons injured and died respectively are reported.  This article is devoted mainly to safety aspects of electrical installation in residential premises.

BASIC PRINCIPLES:

• The installation shall be carried out inconformity with relevant Indian standards mainly, IS-732 and provisions of Central Electricity Authority regulations related with safety.
• All materials, fitting, equipment and appliances should conform to Indian Standards.
• All electrical installation should be done under the supervision of a person holding license issued by competent authority.
• Discussion with Architect/ Civil Engineer about the positioning of concealed conduits, ducts if any should be held at the initial stage.
• Calculation of total connected load in consultation with the owner of the premises.
• Positioning of various electrical appliances in consultation with the owner and Designer.

DESIGN CRITERIA:

            The most important aspect of designing electrical installation is protection of human beings and property and also the proper functioning of electrical installation. The following factors therefore are very important:

• Characteristics of incoming supply to the premises. (Whether single or three phase)
• Demand factor of the total load. (Generally 60% of the connected load in residential premises)
• Emergency lights.
• Environmental conditions.
• Size of the wires/cables to be used.
• Type of wiring and method of installation.
• Protection devices.

PROTECTION FOR SAFETY:

• Protection against electric shock can be achieved by providing Residual Current Devices. The metal enclosure of any electrical equipment should be effectively earthed. The current carrying parts should not be exposed.
• The sizes of wires should be so chosen that there will not be any over load. The wattage of each equipment/gadget should be properly ascertained and then the size of the wire should be selected. Power plug points wiring should be done with independent wires of suitable sizes. Miniature Circuit Breaker (MCB) of suitable size should be installed for each circuit which shall take care of any over load and short circuit. Power consumption of some of the electrical equipment/gadgets are given below for ready reference:

Ref : National Building Code, 2016

• In case of three phase supply, proper color codes (Red, Yellow and Blue for power) of the wires to be used. Black and green color wires are used for neutral and earthing conductor respectively.
• It is to be ensured during testing that wires from one phase are terminated in one switch board.
• For preventing accidents, fires due to thermal effects of electricity, the equipment should be placed at such a position that there is no access to human beings and also chances of ignition with flammable material are minimum.
• The sockets installed in balcony for Diwali Lighting should have IP66 protection (IP 66 is the international protection for water proof and protection against the smallest dust particle.)
• Not less than one meter space has to be provided in front switch board in case of voltage more than 250 V as provided in CEA safety regulations clause no.37
• In bath room the switch board should be above the faucet level.
• The socket provided for geysers should be above the shower level. The switch board shall be sufficiently away from the shower.
• The switch boards should be generally kept at sufficient height away from small children.
• The sockets should have shutters under no –use condition.
• The main distribution board should not be installed more than 6 feet height. It should be easily accessible for operation and maintenance. No paintings or pics to be placed on it to hide it.
• The other utilities like Internet, telephone, audio system, TV cable should be placed away from electrical conduits. They should be laid in different conduits.
• Earthing connection to be provided at all the plug points.

WIRES USED FOR INSTALLATION:

Wires with Copper conductors are used for carrying load current  Following table shows current carrying capacities of wires of various sizes. Proper size of the wires are to be chosen depending on the load to be connected to it.

EARTHING – Earthing forms an integral part of any electrical installation as it protects the user from any leakage in the installation. Earthing conductor is green in color. It is connected to the outer metal frame/enclosure of any electrical appliance so that in case of any insulation failure the current will directly flow to the earth through the earthing conductor instead of flowing through the body of the user. RCCB (residual current circuit breakers) are used to protect from even a minor leakage. As per CEA safety guidelines for residential premises the sensitivity of the RCCB should be 30 mA. Similarly earthing connection is required to be provided to each power socket’s earthing terminal. The earthing conductor of each premises is connected to the main earthing terminal provided in the meter room.

INSPECTION AND TESTING –

• Regular physical inspection of accessible electrical installation is suggested.
• In case of new installation or installation kept disconnected for a period of more than six months, insulation resistance test should be carried out as provided in CEA safety regulations. The insulation resistance shall be done by 500 V DC insulation resistance meter. The value of the insulation resistance measured between each phase and earth should be more than 1 Mega Ohms.
• The resistance of this earthing plate has to be measured every two years. The value should be less than 3 OHMS for residential premises.
• As per CEA safety regulations the low voltage installation shall be tested by electrical inspector or by the supplier every five years. It means it is recommended that the installation should be tested every five years.
• Physical inspection of all the switches and switchgears should be checked. The MCBs may be made ON/OFF for their operation.
• RCCBs tripping shall be checked by pressing the plunger provided on the RCCB at the intervals mentioned on the RCCB.
• The TV or AC switch should be kept off when not in use or when the premises is unoccupied for longer period. It should not be operated only through remote control. Do not put on the mobile charger when the mobile phone is not connected to it. It is wastage of energy.
• If the insulation of any wire is found cut or peeled off, immediate action be taken for its replacement or proper protection be provided.
• There is no life expectancy for wires and cables, but they should be replaced if the insulation has become brittle.
• It is recommended that the electrical appliances shall be got tested by the manufacturer for its replacement if it has become old or is breaking down frequently.

Ref:  i)    The Central Electricity Authority (Measures Relating to Safety & Electricity Supply) Regulations, 2010

ii) Indian Standard – 732 : Code of Practice for Electrical Wiring Installations.