Earthing and bonding are essential safety components of an electrical installation. To identify whether or not the earthing and bonding system is intact in an electrical installation, a test is often required. At ShineTech Electrical, our electricians can identify any issues related to earthing and bonding in your electrical installation, and fix any problems identified.
Difference between Earthing and Bonding
Before we talk about earthing and bonding in-depth, we need to be familiar with two terms: exposed conductive part and extraneous conductive parts.
Exposed conductive parts are generally metal parts of electrical equipment, which can be touched and which are not meant to be conducting electricity when the equipment is functioning normally. However, they can be live if there is a fault.
For example, the metal housing of an oven, microwave or washing machine, metal light switches or metal sockets. The housing of such equipment must always be earthed.
Extraneous conductive parts are metal parts within a building, which do not form part of the electrical system. For example, metal water mains and gas pipes, or steel structural elements in a building. These conductive parts within a building could carry a live current if there is a fault, and must be bonded together.
- All extraneous conductive parts must be bonded.
- All exposed conductive parts must be earthed.
The purpose of earthing in an electrical installation is to provide an adequate alternate path for a fault current to flow to the earth or ground. This will then trigger the automatic disconnection of the power supply to the affected circuit by causing the fuse to blow or the circuit breaker to trip.
The earthing system does not have a significant role in the normal functioning of an electrical installation. However, in terms of electrical safety, earthing is an essential component of any electrical installation.
Without an adequate earthing system in place, when a fault does develop, the fuse won’t blow or the circuit breaker won’t trip. In this situation, the faulty electrical equipment may have live touchable parts. If you touch those live parts, the electricity will flow to the earth through your body instead of through the earthing conductor. This is where you get an electric shock.
Interestingly, for anything to get an electric shock, the current must flow through the body to the earth. That’s why birds can dance on 400kVA overhead transmission lines and yet not get electrocuted!
There are several types of electrical faults. But, when we talk specifically about an earth fault, this is commonly known as a short circuit between the live (Line or Neutral) and the earthing conductors.The two primary causes of earth faults are:
- Faulty electrical accessories or appliances (mainly class I electrical equipment – which includes most of your kitchen appliances) and
- Damaged cables that compromise the insulation between conductors.
Both of these electrical faults are equally dangerous. An unearthed faulty class I electrical appliance can pose a risk of electrocution. A damaged cable can be the source of an electric fire as well as pose the risk of electrocution.
There are two types of bonding: main equipotential bonding and supplementary bonding.
Main equipotential bonding
Main equipotential bonding only applies to premises with metal (not plastic) gas and water mains pipes and/or steel building structures.
With main equipotential bonding, also known as main protective bonding, all extraneous conductive parts (e.g. gas and water mains) must be connected to the main earthing terminal, so that if a damaged live electrical cable were to come into contact with those parts, they wouldn’t become live.
Supplementary bonding usually applies in bathrooms, en-suites and some other special locations.
With supplementary bonding all the metal parts in a single location are connected together with a supplementary bonding conductor. This ensures that there is no difference in earth potential between two separate metal parts. (For example, the radiator pipes, hot and cold water pipes, metal bathtub, electric shower unit, etc.) This is to reduce the risk of electric shock if a fault develops.
If all the circuits serving the location have RCD protection, then supplementary bonding is not required.