Electrical safety concepts

• The following concepts and terms have to be understood:
• Short circuit
• Overloading
• Earthing
• Fuses
• Three pin plug
• Two pin plug

Short circuit

• this is when a wire breaks and comes in contact with the metal casing of an appliance e.g. of a stove
• Current will flow to the casing making it live
• Current flows along the path of least resistance (short circuit)
• Metal casings and appliances must be earthed
• to prevent current from flowing through the person holding the appliance and electrocuting the person

Overloading

• Is when too many appliances are plugged into one power-point/plug
• drawing too much current
• The circuit gets overloaded and
• the wires carrying the current might get hot
• A fuse can be used to prevent overloading

Earthing

• A lot of household and industrial appliances are earthed
• They are connected with a three-core flex wire
• Sockets have a third socket to which the earth wire is attached
• This wire is connected to the metal casing of the appliance
• If there is a fault in the appliance and a short circuit occurs current will flow to the earth via this earth wire
• More current will flow through the earth wire than the neutral wire
• And the fuse will blow due to overloading
• This breaks the circuit
• The wires are run in PVC conduits/pipes
• The earth wire is grounded using a thick wire in the earth
• When steel conduits are used (this is now very rare) they are earthed by grounding them as well

Fuses

• Fuses are made up of a thin wire
• Each wire have its amperage rating for example 13A
• The fuse is then attached to the live wire in a circuit
• In the event of a power surge or an overload the fuse wire blows as it cannot handle any current that exceeds its rating
• For example a 13A fuse will only be able to handle 13A and any current exceeding that will result in the fuse blowing
• When it blows it breaks the circuit

Three pin plug

Three pin plug. Image credit physicsnet.co.uk

• These plugs carry power from a household socket to the appliance
• EAch wire in the power circuit makes contact with wires in the appliance
• The live wire is connected to the live wire in the appliance and
• The neutral wire makes contact with the neutral wire in the appliance
• the wires are also colour coded
• The live wire is brown
• The neutral wire is blue
• the earth wire is green and yellow
• Three pin plugs also have a plug

Two pin plug

A two pin plug

• Some electrical appliances have two pin plugs instead
• These only have the live and neutral wires
• They have no fuse
• They usually draw only a little current
• They are also well insulated and usually made of plastic
• There is no risk of the user being electrocuted

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