Complete information on the Concept of Electrical Safety

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The world over, the concept of safety of household electrical appliances implies that it should ensure safety of the persons and surroundings when used under conditions:

(a) Specified for the purpose

(b) Normally met with in actual practice though different from the specified conditions of negligent use ignoring the given precautions, instruction and of improper or willful wrong use

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These conditions should be satisfied not only when it has been in use for some time.

To enable manufacturers to incorporate all the above features in the appliances produced in India. The ISI has made available IS: 302-1973. The standard was first published in 1951.

IS-302-1973 provides guidance or important constructional features; methods o test and requirements for individual appliances have been covered in separate specifications which in all cases refer to IS-302-1973 for details.

Safety criteria and stipulations:

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Keeping in view the possibilities of the use of the appliances under different conditions, provisions have been incorporated in IS 302-1973 to ensure safety of the personnel during operation and handling.

Some of the major stipulations made in the standard along with methods to verify the prescribed features event at the design prototype stage are discussed in the paras who follow Protection against electric shock –

An electric shock results from contact with a live part. It is, therefore, important to check openings to prevent accessibility to the live parts which may become live under defective conditions.

The checking as effected with the help of standard test probes as given in IS 302-1973 the specifications, guards apertures, etc., shall be so designed that it will not be possible to make a contact with-live part with the standard test finger.

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To ensure safety to the operator and surroundings IS 302-1973 stipulates that appliances as well as their surroundings shall not attain excessive temperature in normal use. The standard fixes for the temperature-rise of various parts including external enclosures of the appliances, handles grips, knobs, etc.

Electrical insulation is the heart of an electrical appliance. It gives an inherent protection against electric shock in addition to serving other functional requirements. Excessive leakage current which is responsible for electric shock also damages the insulation due to slow heating thus reducing the safe operating life of an appliance.

It is important that the insulating materials used must be free from voids and other kinds of defects. These features are checked by leakage current and high voltage test specified in IS 302-1973.

Moisture resistance:

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While considering safety it is implied that any appliance designed to perform its assigned duties should perform those duties safely and reliably not only when it is new but also during its extended use. An electric kettle is likely to be subjected to spillage of liquids in normal use.

There, is likelihood of dripping of water in water heaters installed in bathrooms. The design of the appliances should be such that even in case like this safety is not impaired and that there is no likelihood of getting a shock if one touches/handles these appliances.

Furthermore, during rainy season, humidity in closed places, particularly kitchens and bathrooms, may go as high as 95 per cent and appliances should be able to function satisfactory under such conditions as well. IS: 302-1973 specifies the tests that are to be carried out on different types of appliances to ascertain their moisture resistance. For this purpose, the appliances are subjected to humidity treatment at 95 per cent relative humidity for a specified period.

Abnormal Operation:

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It is quite likely that a housewife may put on an electric kettle for making tea may forget to add water or pull off the kettle after use.

A similar situation:

It arise in the case of other appliances also like electric irons and immersion heaters Further, one may switch on a food mixer but may either forget to put the ingredients in the food mixer jar or may overload it beyond its capacity.

Incidents of these types are certainly not among the recommended use but they are not uncommon. Operation of an appliance in such situation is called abnormal or careless or an attempt to operate defective equipment can also not be ruled out.

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