When a cable is damaged we actually want an earth fault to happen because the electricity will switch off and become safe.

If a damaged cable is touching some metal, we could get a shock if we touch the metal too. But, if we connect the metal to the earth, the electricity will escape to the earth and we will be safe. We use a green and yellow wire to make this very important connection.

When a live wire touches metal that is connected to earth, lots of electricity will flow through the wires. This is called an earth fault. Just like a short circuit, the fuse or circuit breaker notices the big change and switches off the power to make it safe. 

Electricity normally stays in the live wires but it really wants to get out and find a way to the earth. When we say earth, we mean the actual ground.

Sometimes when the electricity leaks out of a damaged cable it finds that the best way to go to the earth is through you. Usually, because you or something you are touching is on the ground. Because the leaked electricity always finds its way to earth we call this an earth leakage fault.

How do we protect against earth leakage? Enter the RCD. The ‘Residual Current Device’ constantly monitors the Line and Neutral live wires; these wires are brown and blue. The RCD checks that electricity is coming and going as normal. If some electricity is missing then it could be leaking and giving someone an electric shock. The RCD notices this small leak and will instantly switch off the power to make it safe.

 

 

If a wire provides too much electricity for too long, it can get hot and become damaged or even cause a fire. This usually doesn’t happen because the electrician who installed the wires has designed the cable correctly. Sometimes if we plug in too many high power items we can cause an overload to occur.

Overload protection is designed to match the cable that is used. This is an important aspect of electrical design because the circuit breaker must be sensitive enough to switch off the power before the cable becomes damaged.

When a fuse is replaced it is important to replace it with the correct size. Using the wrong fuse will cause the cable to burn before the circuit is automatically switched off.

When electricity jumps across the air it appears like lightning. This is called an Arc. Arc faults can cause fires especially if the cable is near other items that could catch fire easily. There are two main types of arc fault:

1. Series Arc Fault. This happens when there is damage to one wire in a cable or if cable connections are loose. The electricity struggles to get through and it tries to jump across the gap.
2. Parallel Arc Fault. This happens when there is damage to two wires and the electricity jumps from one to the other.

Sometimes the fuse, circuit breaker or RCD will switch off parallel arc faults. Both series and parallel arc faults can be detected by an AFDD or ‘Arc Fault Detection Device’. These devices are not yet commonly used but are becoming more common where the risk of fire is high.

 

Electronics are often sensitive to power surges. If the voltage increases too much due to nearby lightning strikes or other conditions, our expensive electronic devices could become nothing more than a fancy paperweight. Adding levels of surge protection to an installation will remove the extra electricity and send it straight to earth.