Mains Electricity

Mains Electricity

Mains Supply

  • UK mains supply uses an alternating current (AC) of approximately 230 V and frequency of 50 Hz.
  • Mains electricity can be extremely dangerous and can cause fatal electric shocks and fires.
  • Live, neutral, and earth are the three types of wires used in a UK mains plug.
  • The live wire carries the voltage, the neutral wire completes the circuit, and the earth wire is a safety wire to prevent electrical shocks.

Circuit Breakers and Fuses

  • Fuses and circuit breakers are devices used to protect circuits and appliances from damage. They work by breaking the circuit if too much current flows.
  • A fuse is a piece of wire which is designed to melt and break when the current flowing through it exceeds a certain level.
  • A circuit breaker is an automatic switch that stops the current if it exceeds a certain level.

Power and Energy Use

  • A device’s power rating represents the maximum amount of power the device can handle safely. It is measured in watts (W) or kilowatts (kW).
  • The energy used by an appliance can be calculated using the formula: Energy (in kWh) = Power (in kW) x Time (in hours).
  • Efficiency is a measure of how well an appliance converts input energy into useful output. It can be calculated as: Efficiency = (Useful power out ÷ Total power in) x 100%.

Energy Transfer and Work Done

  • When electric charges move through an electrical device, work is done and the energy transfer takes place.
  • In an electrical circuit, energy is transferred from the power source (battery or mains) to the components in the circuit (for example a bulb, resistor, or motor).
  • The formula for work done is: Work done = Force x Distance. In an electrical context this is: Work done (Joules) = Energy transferred (Joules)

Safety Precautions

  • Various safety features are part of the UK mains plug including: the casing is made of insulating plastic to prevent electric shock, it has a built-in fuse to prevent overheating, and the earth wire provides an alternative path for electric current to flow in case of a fault.
  • Double insulation is a safety measure found in electrical appliances where the live parts are surrounded by two separate layers of insulation to prevent electrical shock.
  • Always switch off and unplug electrical appliances before working on them.

Alternating and Direct Current

  • In direct current (DC), charges always flow in the same direction, such as in a battery-operated device.
  • In alternating current (AC), charges continuously change the direction of flow. The UK mains supply is an example of this.