Most 240 volt power tools have a three-pin plug that allows the tool to plug into the mains power system. Each pin is connected to a wire - active, neutral or earth.

The active and neutral wires provide the circuit that lets electricity flow through the tool. The earth wire is there in case of an electrical fault inside the tool, so that the power can flow straight to 'earth' instead of through the person holding the tool.

Another safety device used to guard against electrical problems is a circuit breaker or fuse on the active wire. If there is a surge in power, the fuse is designed to 'blow', or the circuit breaker to 'trip', which cuts off the power in that circuit. This allows you to find the fault and fix it before you replace the fuse or turn the circuit breaker back on again.

Below is a simple diagram of an electrical circuit for a power tool. At the supply end, the electricity is delivered via power lines which come from the power station. At the tool end, the three pin plug connects the active, neutral and earth wires to the circuit via a power point.

Some of the wires are left out of this circuit. See if you can connect them up by clicking on one terminal and then the other terminal that the wire would run between.

The first wire is done for you. It runs from the terminal block (connected to the powerlines) to one end of the circuit breaker.