Electrical Safety

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L&T SWITCHGEAR
SAFE & SURE

ELECTRICAL SAFETY

E S P SERVICE MANUAL

GENERAL

Electricity is good servant but bad master. It can prove to be very dangerous if circuits are not properly protected. The major fault that appears in electrical network or equipment is termed as short circuit. In short circuit, the supply phase and neutral or earth is short circuited accidentally due to foreign metallic substance coming in contact with phase & neutral or earth or due to overload thereby damaging the insulation resulting in short circuit i.e. directly connected resulting in heavy current flow called "short circuit current". This high current heats up the terminations, switches, plugs & cable due to which temperature rises to such a high degree that it is sufficient to generate sparking which further leads to fire.

PROTECTION OF CIRCUITS : In order to restrict the short circuit currents and also to.cut off or isolate the faulty circuit from electric supply so that high short circuit current is interrupted before fire starts, appropriate protective devices need to be used as given below : Rewirable Fuses : It is strongly recommended that fuse wires of correct current rating should be used. DO NOT INCREASE THE FUSE CAPACITY FOR PREVENTING OR ELIMINATING FREQUENT FUSE BLOW-UPS. It is essential to locate the causes and eliminate the same. Replacing fuse wires of higher capacity may invite troubles in the form of fire & damage to supply system and surroundings. HRC Fuses : High Rupturing Capacity (HRC) fuses are capable of clearing short circuit & arcs. However, they are much more costlier and hence, application is mostly restricted to commercial & industrial wiring or higher capacity loads. MCBs : Miniature Circuit Breakers are gaining increasing prominence in household and distribution wiring in shops & commercial establishments as it effectively forms combination of switch & fuse with specified level of fault clearing capacity. It can be used to protect individual circuits. It has an advantage since no replacement is required and it can be reset on elimination of fault and switched on again.

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ELECTRICAL ACCIDENTS

Electrical accidents are caused mainly by careless use of electricity, such as : 1) Lack of knowledge about functioning of equipment. 2) Using faulty electrical cords/sockets. 3) Use of extension cords without taking proper precautions. 4) Improper earthing of the device. 5) Faulty designs/inter-locks. The major factor which plays a vital role in severity of electric shock is amplitude of current, and part of human body through which it passes. For accident to happen, current of sufficient magnitude must flow through vital organ thus impairing its function. When a person accidentally touches a live wire, the severity depends upon the skin resistance of that person, which varies from 1 K Ohm to 11 M Ohms. Generally current amplitude more than 30 milli Amps is sufficient to give shock which can be fatal.

METHODS OF ACCIDENT PREVENTION Grounding : • It has been observed that in many industrial, domestic and commercial premises, grounding system has become unreliable. It is essential that earth resistance should be as low as possible. It is specified that for protective purpose, the same should not exceed 0.2 Ohms. Under no circumstances, earthing wire in the house/flats should be connected to water pipes. This not only gives shock in your premises but to someone else also. Water pipes are coming down from terrace and are not earthed.



Isolation transformers: Use of isolation transformers reduces the amount of leakage current considerably.

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ELECTRICAL FIRES

Electrical supply is available at the tip of the finger. As a source of power in some ways, it is less hazardous than steam or other prime movers. Failure to take proper precautions in its use creates conditions which can result in injury, fatality or damage to property. Elimination...
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