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Electrical Earthing & Bonding Explained

Earthing and bonding is a less 'glamorous' aspect of the work an electrician carries out in your home or workplace. You may not even notice it, but it is the most important part of an Electrical Installation.

Earthing and Bonding - Gas and Water
Typical Earthing and Bonding

Earthing and bonding work is carried out to ensure the electrical installation is safe and will protect People/Animals, Equipment and the Installation under a fault condition. If done incorrectly, the electrical current may not flow down the earth connection thereby increasing the risk of electric shock and even fires.

A Qualified, Registered Electrician will always ensure that the earthing and bonding is correct on your electrical installation, however this very important work is nearly always overlooked by an unqualified person.

What is Earthing?

This is the Main Earth for your Electrical Installation. It's job is to automatically disconnect the supply in the event of a fault.

Depending on the earthing arrangement of your property, it could be a green/yellow wire running from your Consumer unit to the Main Supply Head/Cable or from your Consumer unit to an Earth Rod/Matt Located outside (usually).

In modern Electrical Installations, the earth wire would typically be 16mm for a T-N-CS earthing arrangement.

T-N-S systems are now assumed to also be T-N-CS as over the years, DNO maintenance have converted the systems in the street.

For a TT system (Earth Rod), the Main Earth could be as little at 2.5mm, although it would usually be 10/16mm.

What is Bonding?

There are 2 main types of bonding.

  1. Main Equipotential Bonding

  2. Supplementary Bonding

Why do we bond to Gas & Water Pipes?

This is called Equipotential Bonding. Bonding is necessary in buildings with metal gas and water supply pipes, it also includes structural Steel, Oil pipes and lightning conductors.

This is because metal pipes have the potential to carry electrical currents or faults from outside into your home/business. This is very dangerous and can lead to all or some metallic items in your home becoming live, which could be fatal. Without bonding to the gas and water installation pipes, the pipework becoming live is greatly increased.

It is also a very important electrical regulation and your electrical installation cannot be certified without it.

How do I know if my Main Bonding is correct?

A quick way to find out if your property has correct earthing and bonding, take a look at your main gas meter. You should see a green and yellow wire (typically 10mm) attached to it. In addition, also take a look at your main water stopcock, you should see a similar connection. Earthing and bonding work are both visually similar in terms of the green and yellow colour identification. Do remember though that in order for an electrical installation to be deemed safe and satisfactory, bonding must be carried out within 600mm of the meter or stopcock or where the pipes enter the property.

In some cases, it may look like the bonding is connected but actually isn't. The only way to confirm this is by carrying out a continuity test.

So what about Supplementary Bonding?

Supplementary Bonding isn't as widely used anymore. It was mainly installed in bathrooms to provide what's called additional protection. With the use of RCD's this type of bonding is no longer required.

Want to know more about RCDs? Click here.

I'm not sure about my Electrical Earthing and Bonding...

Now is the time to call the professionals. We've covered the basics but only brushed the surface. If you have any doubts about the safety of you electrics, call a Qualified, Registered Electrician.

Here at Suresafe Electrical Services Ltd, we specialise in Electrical Safety.

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