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Electrical safety 

    Electrical hazards

Electricity  is a useful form of energy  but it can also be very dangerous. There are lots of ways in which we can be electrocuted including: 
  • Touching uninsulated electrical cables.
  • Overheating cables or  overloaded circuits.                                 
  • Short circuit due to worn, damaged or incorrectly wired plugs 
  • allowing water or wet objects to enter plug.
  • pushing metal objects into plug sockets.

  Electrical Safety:
  • Insulation. 
  • Plugs.
  • Fuse.
  • Circuit breaker (RCCB).
Insulation 

A flexible coating of an insulator is often applied to electric wire and cable,

 this is called insulated wire.

Since air is an insulator, in principle no other substance is needed to keep power where it should be. High-voltage power lines commonly use just air, since a solid (e.g., plastic) coating is impractical. 

However, wires that touch each other produce cross connections, short circuits, and fire hazards.

 Finally, wires that expose voltages higher than 60V can cause human shock and electrocution hazards. Insulating coatings help to prevent all of these problems.


Electric Plug 

Electrical circuits, cables, plugs and appliances are designed to reduce the chances of receiving an electric shock. You should know the features of a correctly wired three-pin mains electricity plug and be able to recognize errors in the wiring of a plug.

A mains electricity cable contains two or three inner wires. Each has a core of copper, because copper is a good conductor of electricity. The outer layers are flexible plastic, because plastic is a good electrical insulator. The inner wires are colour coded:

Colours of inner wires within a cable and the plug

          Color             Wire                                               Function                                           
 Brown Live Is held as a voltage of 230 V and provides the current 
 Blue Neutral  Completes the circuit 
 Green & Yellow Earth  A safety wire to stop the appliance becoming live, It is connected to a copper conductor buried in the ground.



  The features of a plug are:

  • The case is made from tough plastic or rubber, because these materials are good electrical insulators.
  • The three pins are made from brass, which is a good conductor of electricity.
  • There is a fuse between the live terminal and the live pin.
  • The fuse breaks the circuit if too much current flows.
  • The cable is secured in the plug by a cable grip. This should grip the cable itself, and not the individual wires inside it.
The blue neutral wire goes to the left, the brown live wire to the right and the green and yellow striped earth wire is on top. The fuse fits next to the live wire.

The inside of a plug

The diagram shows the key features of a correctly wired three-pin mains plug.

Where does each wire go?

There is an easy way to remember where to connect each wire. Take the second letters of the words blue, brown and striped. This reminds you that when you look into a plug from above:

blue goes left, brown goes right and striped goes to the top.


 Why electrical appliances are earthed?

Earthing

close up of the cooker shows the live, neutral and earth wires going into the mains, and an extra wire coming from the earth socket connecting to the casing

Earthing of an electric cooker:

Many electrical appliances have metal cases, including cookers, washing machines and refrigerators. The earth wire creates a safe route for the current to flow through if the live wire touches the casing.

You will get an electric shock if the live wire inside an appliance, such as a cooker, comes loose and touches the metal casing. However, the earth terminal is connected to the metal casing so that the current goes through the earth wire instead of causing an electric shock. A strong current surges through the earth wire because it has a very low resistance. This breaks the fuse and disconnects the appliance.




Some appliances, such as vacuum cleaners and electric drills, do not have an earth wire. This is because they have plastic casings, or they have been designed so that the live wire can not touch the casing. As a result, the casing cannot give an electric shock, even if the wires inside become loose. These appliances have double insulation.


 

Fuses


The fuse breaks the circuit if a fault in an appliance causes too much current flow. This protects the wiring and the appliance if something goes wrong. The fuse contains a piece of wire that melts easily (has a low melting point). If the current going through the fuse is too great, the wire heats up until it melts and breaks the circuit.

Fuses in plugs are made in standard ratings. The most common are 3A, 5A and 13A. The fuse should be rated at a slightly higher current than the device needs:

·        if the device works at 3A, use a 5A fuse

·        if the device works at 10A, use a 13A fuse

A 13A fuse with a low melting point wire

Cars also have fuses. An electrical fault in a car could start a fire, so all the circuits have to be protected by fuses.



Circuit breaker (RCCB)


Fuse & RCCB



What is RCCB?
 Residual Current Circuit Breaker, or RCCB in short, could prevent any unnecessary and unfortunate death in your family. RCCB is a device in your house that detects and measures current leakage. It is installed in the electrical distribution box inside your house. RCCB is a device that detects leakage current, which is why, it safeguards you from fire hazards, electric shocks, or even worse, electrocution. However, as an electromechanical device, RCCB may subject to failure after a period of time.http://www.neweysonline.co.uk/neweys/images/site/products/large/044_1008_SC03_RMG250302_large.jpg


How does RCCB work? 
RCCB is a device that detects leakage current, During the leakage, some of the electric current will pass through the human body so there will be a difference in the current value between the live and the neutral, the RCCB detects that automatically and open the circuit. That is why, it safeguards you from fire hazards, electric shocks, or even worse, electrocution. 
So we can say that it is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit.

       Unlike the fuse, which operates once and then must be replaced when melted (blown), the circuit breaker can be reset (manually or automatically) to resume the normal operation after the repair.



How does a Residual Current Circuit Breaker Work?

This type of circuit breaker works by comparing
the current going in to an appliance with the current coming out.
When an appliance is working correctly
all of the current entering the appliance through the live wire
is returned to the power supply through the neutral wire.
In this picture the strength of the magnetic field is the
same in both coils because they both have the same current.


 
If something goes
wrong with the appliance
some of the electric current will flow through the earth wire.
The amount of current flowing through the neutral wire
decreases and now there is a difference between the
current entering the appliance through the live wire and the
current returned to the power supply through the neutral wire.
This difference is called the residual current.
The coil connected to the neutral wire now has a
weaker magnetic field than the coil connected to the live wire.
The iron rocker turns about the pivot and the
contacts are disconnected which switches off the
appliance and makes it safe. See the picture below.

The RCCB acts to switch off




A summary on Domestic electrical components and devices


Fuse, Plug, RCCB



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