Why are domestic electrical appliances earthed?
You may have noticed that most electrical items have three wires within them, a live wire, a neutral wire and an earth wire. Have you ever wondered what the different wires do? You might also have heard the term “earthing” too when having electrical work done on your home. But what do these terms mean? And why are electrical appliances earthed?
Read on to find out more.
What is earthing?
Earthing is a safety feature of domestic installations and appliances. It allows electrical currents to discharge into the earth away from users, keeping them safe from shock. You can tell that a domestic appliance is earthed, as it will have three wires, rather than two.
Electricity will always want to return to earth. It’s why lighting hits the ground. This is to do with how electricity works. The negative electrons (microscopic particles) flowing through a circuit that makes up electricity are attracted to the positive charge of the earth. The electrons will always be attracted to the positive charge (opposites attract, after all!), and will flow as quickly as possible to that point.
An electrical installation should have a means of earthing. In the UK there are 3 main types of earthing systems. 2 of them (TN-C-S and TN-S) are provided by the electricity board and another (TT) refers to the homeowner having a metal stake inserted into the ground. This is known as an Earth Rod.
What happens when they aren't connected?
If an appliance isn't earthed when it should be, it's possible that it will cause harm to people who touch it.
Imagine your ceiling light had a fault inside it that you didn't know about; the live wire has become disconnected somehow and is touching the metal cover of the light. If that ceiling light had no earth wire, and you accidentally touched the metal cover, the electricity would flow through you, giving you an electric shock.
An earth wire provides a way for the electricity to flow out of the device without going through you.
Why do some appliances not have earthing wires?
If an appliance has a metal chassis, then it will act as a conductor. This means that any electric current flowing through the appliance will flow into the earth. However, if there is no metal chassis, the appliance acts as a resistor. This means that the current will not flow into the earth. Instead, it will continue to flow through the appliance until it reaches a point where it cannot go any further. At this point, the current stops flowing.
If an appliance acts like a resistor, it is unlikely that you will get an electrical shock from touching the object. Therefore, these appliances often do not have earth wires. Some appliances and accessories do have a metal case, but because they are Class 2 appliances, they don’t require earthing due to already being double insulated.
How to check if your appliance is earthed.
Appliances that have three wires are earthed. Some appliances have labels on them if they do not require earthing. In which case these should be Class 2 appliances. In the UK an appliance will either require earthing or be Class 2.
The best way to ensure that your whole electrical circuit is earthed properly though is to ask an electrician to survey your whole system. They will ensure that earthing is in place and can advise if there is an issue.
PAT testing
PAT testing (Portable Appliance Testing) is the electrical safety test required for all appliances to ensure that they are properly earthed and safe to use. If you live in a rented property, your Landlord should conduct PAT testing on each appliance he leaves for you.
Earthing keeps us safe
Remember, earthing is a very important safety feature, designed to protect everyone in your home. Make sure that you only purchase appliances from reputable manufacturers, and check they have safety features and certificates. For more information on having your circuit tested, don't hesitate to get in touch with us and we will be happy to assist you.
