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ELECTRIC SHOCK is the passage of current through the body of such magnitude as to have significant harmful effects. How, then, are we at risk of electric shock and how do we Protect against it?

There are two ways in which we can be at risk.

 

1.    Touching live parts of equipment or systems that are intended to be live. This is called direct contact.

2.    Touching conductive parts which are not meant to be live, but which have become live due         to a fault. This is called indirect contact.

The conductive parts associated with indirect contact can either be metalwork of electrical equipment and accessories and that of electrical wiring systems (e.g. metal conduit and trunking), called exposed conductive parts, or other metalwork (e.g. pipes, radiators and girders), called extraneous conductive parts.

 

How to protect yourself against direct contact:

 

How can we prevent danger to persons and livestock from contact with intentionally live parts? Clearly we must minimize the risk of such contact and this can be achieved by

• insulating any live parts

• ensuring any un-insulated live parts are housed in suitable enclosures

and/or are behind barriers.

 The use of a residual current device (RCD, inbuilt Distribution board breakers) cannot prevent direct

Contact, but it can be used to supplement any of the other measures taken, provided that its rating, is 30 mA or less and has a tripping time of not more than 40ms at an operating current of 5amps.

 

It should be noted that RCDs are not the panacea for all electrical ills, they can malfunction, but they are a valid and effective back-up to the other methods.

 

They must not be used as the sole means of protection.

How to protect against indirect contact:

How can we protect against shock from contact with live, exposed or extraneous conductive parts whilst touching earth, or from contact between live exposed and/or extraneous conductive parts?

 

The most common method is by earthed equipotential bonding and automatic disconnection of supply (EEBADS).

 

All extraneous conductive parts are joined together with a main equipotential bonding conductor and connected to the main earthling terminal, and all exposed conductive parts are connected to the

Main earthling terminal by the circuit protective conductors. Add to this, overcurrent protection that will operate fast enough when a fault occurs and the risk of severe electric shock is significantly reduced.

 

What is earth?

The thin layer of material which covers our planet – rock, clay,

chalk or whatever – is what we in the world of electricity refer to as

Earth.

So, why do we need to connect anything to it? After all, it is

not as if earth is a good conductor.

It might be wise at this stage to investigate potential difference

(PD).

A PD is exactly what it says is: a difference in potential

(volts). In this way, two conductors having PDs of, say, 20 V and

26 V, have a PD between them of 26 – 20 = 6 V. The original PDs

(i.e. 20 V and 26 V) are the PDs between 20 V and 0 V and 26 V and

0 V. So where does this 0 V or zero potential come from? The simple

answer is, in our case, the earth. The definition of earth is, therefore,

the conductive mass of earth, whose electric potential at any point is

conventionally taken as zero.

But sincerely we are getting bored already with all this explanation.

But if you feel little shock when touching the metal parts of your home appliances, {DVDs, home theater’s, TVs, washing machine, fridge etc}. Then you need to add one more trick to your sleeves, because in less than no time at all it might grow to become a great disaster.

See figure1 above.

 

We can help.

 

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