GCSE Physics Revision: Mains Electricity

12th April 2017

GCSE Science – Physics – Mains Electricity  

KEY STAGE 3 – GCSE Science Revision Guide – GCSE Physics


Use this Revision Guide to remember all the Key Study Points in the GCSE Syllabus and get Full Marks in your GCSE Physics Exam.

What is “Mains” Electricity?

The ‘main’ electricity supply to your home is referred to as the “Mains Electricity Supply”.

What voltage is the mains supply to your home?

By law, the ‘nominal voltage’ has to be 230 Volts (with a tolerance range of + 10% or -6%).

Is 230 Volts potentially dangerous?

YES, it can kill you!

But, there are ways to make the mains electricity supply safer.

For example:

Fuse Boxes / Circuit Breakers

  • The mains supply is normally supplied via/to a central point in the house and then distributed from there, this is commonly referred to as the ‘consumer unit’, ‘distribution board’ or ‘fuse box’:

    • The fuse box controls and distributes the electricity throughout the home

    • The fuse box contains three important safety features:

  • Main Switch: this turns on/off the entire mains electricity supply to the home.

  • Circuit Breakers: these operate as fuses and ‘break’ the circuit in the event of a potentially dangerous electrical surge (protecting us and any electrical devices from harm/damage).

  • Residual Current Devices (RCD): these are further safety features which offer more specific protection than fuses or circuit-breakers (they switch off the electricity supply immediately if there is a fault, for example if you cut a cable by mistake).


Insulated electricity cables and appliances

  • most cables in your home are made of copper wire, because copper is a good (and cost-effective) conductor

  • in order to protect us from the dangerous effects of electricity, the copper wire is sheathed (covered) in plastic or rubber (these are good insulators)

  • these insulators stop the electricity being conducted from the copper wire through our bodies (potentially resulting in injury or even death).

Wall sockets and plugs

  • In order to plug your television into the mains supply, you will have to ‘plug’ the appliance into a ‘wall socket’ and switch the supply on to allow current to pass into the appliance.

  • The ‘plug’ contains a fuse, which in a similar manner to a fuse box, will interrupt or break the electricity supply if there is an uncontrolled surge in power or a dangerous fault in the electrical appliance (e.g. television).


  • Enclosed in a plastic or rubber (insulators) case so that it can be handled safely

  • Three brass pins (brass is a good conductor and does not corrode easily)

  • Contains a fuse between the live pin and live terminal (the fuse acts as a circuit breaker if there is too much current or an unexpected surge)

  • In most plugs, a ‘cable grip’ secures the main cable and ensures there is no movement of the individual wires and that they do not become loose or detached from their connections.

NOTE: It is important that you know how to wire a plug!

  • ‘Mains electricity cables’ usually contain three smaller coloured wires:


    • BROWN = LIVE


Use this trick to remember HOW to wire a Plug:




Why do we ‘Earth’ mains plugs?

This ensures that the electricity has a safe route for current to flow through (into the earth) if there is a loose or defective cable which is touching a conductor (metal) belonging to the appliance

  • if there was no earth cable for the current to safely dissipate into and someone touched the metal part of a defective appliance, they could get quite an electric shock!





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