Cables, Plugs and Power

Mar 18
In this free sample of the science revision tuition programme we look at the two types of electrical supply, alternating current (AC) and direct current (DC). 

Understanding AC and DC Electrical Supply
Two types of electrical supply, alternating current (AC) and direct current (DC), exist.
The potential difference does not change in direct current, so the current travels in one direction.

Alternating Current (AC) and its Properties
In an AC, the potential difference constantly changes direction or polarity, so the flow of electrons repeatedly changes direction. This is done 50 times a second, giving the frequency of the mains electricity in the UK of 50 Hz and 230 V. This is because of how generators make electricity.

Electrical Cable Types in Home Appliances
Most of the cables in our homes that connect appliances to plugs are three-core cables. Only appliances that have plastic housing and can’t conduct electricity to the user if there is a fault can have two-core cables.

Wiring System and Colours in UK Homes
Each of the three wires has a different colour and this shows the job in the circuit:
  • The brown wire is the live wire – remember brown burns; this provides the alternating potential difference at 230 V
  • The neutral wire completes the circuit and will still have a current flowing through it, although it has 0 V.
  • The Earth wire is green and yellow. This is a safety feature and stops the casing from becoming live. It only carries a current when there is a fault. It has 0 V.

Electric Shock and Earthed Objects
Your body is in contact with the ground – it is an earthed object. Your body also has 0 V, so if you touch a live wire, there is a large potential difference between the wire and yourself and the current will flow. This causes an electric shock.
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