Earthing and Bonding. The Difference Between them

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1) What is earthing and bonding? 

Well, earthing provides a safe path for current to flow to in the event of a fault with your electrical system. 

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2) What is Earthing?

Earthing is the process of connection of any exposed conductive parts of an electrical installation to the main earthing terminal for the electrical installation. Earthing gives the electrical system a low resistance fault path for electrical faults to travel away from the installation and to enable protective devices to disconnect the power quickly enough to prevent electric shock, fire and damage to the wiring system. 

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3) What is Bonding?

Main equipotential earth bonding connects extraneous conductive parts in your home together to ensure that in the event of a fault, everything metal is at the same voltage meaning you shouldn’t receive a fatal shock. 

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4) What are Extraneous Conductive Parts?

This sounds complicated but its not. An extraneous part is something that is NOT part of the electrical system but presents a HAZARD when an electrical fault occurs. That is, an EARTH PATH. 

Think of the copper water pipe in older homes. These pipes typically went directly into the ground and were a reasonably good conductor of electricity. 

The problem with this is that its NOT THE EARTH that was intended to be used by the electrical system. Most electrical systems in our homes have an earth connection from the supplier which is a really good LOW RESISTANCE path to earth. 

Extraneous conductive parts such as copper pipework will potentially be a danger when electrical faults occur so we use thick copper wires to connect them to the earth that is provided for the electrical system to ensure that there is no difference in POTENTIAL between the live part we might touch and the metal pipework when faults occur.

That’s the basic explanation. Don’t worry though, we get it and we make sure that it is done right for you.

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5) Can my home work without bonding and earthing? 

Your homes electrical system will function perfectly well under most circumstances without the need for earthing and bonding. But that means problems. 

The issue is, if everything appears to be working correctly without issues or if “we have never had a problem” then no – one ever thinks to get anything checked out. 

The real issue arises when there is a fault. If there is no earthing and bonding or if the earthing and bonding has been carried out poorly then it is very possible that somebody could receive a fatal shock. 

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6) Safety Aspects

Earthing and Bonding is one of many safety aspects that electricians consider when we wire or rewire your home. Essentially, we want to make sure that if there ever is a fault with wiring, appliances, or electrical accessories in your home that your electrical system will detect the problem and shut off the circuit before anyone is hurt.

(Light fitting with no earthing)

There are other safety aspects that we use and consider when we design your electrical system. We use Electric Shock Prevention Devices (RCDs) which detect when there may be someone receiving a shock and switch off. Fuse in consumer units, plugs and incoming equipment are also there to disconnect the supply if a fault should occur. 

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7) Additional Work on Electrical Systems

Earthing and Bonding is a vital part of any electrical installation. Before any additional work can be carried out on an electrical system, your electrician should check the earthing and bonding and make sure that everything is safe to add extra wires, lights, or sockets on to. We can install earthing and bonding for you if it is needed. 

If you have any concerns about your home electrical system, have had minor shocks or tingles then please call us for a chat, you may need a safety inspection and fault finding carried out on your system to check for problems. 

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8) How thick should bonding be?

This does depend on a number of factors. In most cases electrical bonding should be 10mm copper cross sectional area. In some cases, it may need to be larger where longer cable runs are required. 

This protective conductor is absolutely vital to most electrical installations and we have to ensure that the copper is good and thick creating a highly conductive path to earth to prevent any difference in resistance between the Earthing Conductor and the Exposed parts. 

By doing this, we will absolutely minimise electrical current flow between the two parts and ensure that there are no potential differences (difference in voltage).

(Bonding Clamp Installed on a Gas Pipe)

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9) Can I install Main Bonding DIY?

Absolutely not unfortunately. 

There are requirements that have to be met for bonding arrangements in order to ensure electrical safety is maintained. These requirements include tests prior to the installation of the bonding to ascertain if the installation requires it.

In some cases, installing Main Equipotential Bonding actually INCREASES the electrical hazards if the parts that are bonded do not require bonding. For safety reasons, an electrician will determine through electrical testing if a metal part is an extraneous conductive part or not.

Only through correct testing and interpretation of the results can electrical earthing and bonding be installed to the required standard thereby minimising the risk of electric shock.

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10) What is an exposed conductive part?

Slightly different to an EXTRANEOUS conductive part. An exposed conductive part is PART OF THE ELECTRICAL SYSTEM, is conductive and can be touched. 

Think of the case of an electric oven. Most of these are exposed conductive parts that may become live during electrical faults. The front of a chrome or other metal socket or switch is also an exposed conductive part.

These parts are NOT required to be bonded but are required to be earthed.

The photograph shows a metal face plate that became live at 230 volts due to an electrical fault in the street. We were called to investigate total power loss and ended up calling the distribution network operator out to fix their potentially LETHAL issue.

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11) What is supplementary bonding?

Supplementary bonding is installed where different parts of an electrical installation need to reach the same earth potential. That is, where in the event of a fault, all exposed conductive parts and extraneous conductive parts should be at substantially the same potential. 

Think of a bathroom as an example, the taps, the radiator, the metal casing of a light fitting and other pipework all need to be connected together with earthing to ensure that there are no voltage differences. This is where supplementary bonding comes in. 
The supplementary bonding connects all accessible metal parts of electrical equipment and earthed non-electrical equipment together to ensure that when an electrical fault occurs, the risk of electrical shock hazards is minimised.

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12) Why would the circuit breaker not trip?

There are instances where a circuit breaker will not trip. A circuit breaker is an overload protection device and prevents any damage from occurring to cables under electrical overload conditions. 

A circuit breaker or MCB as it is known, would not disconnect the power to the electrical circuit under certain conditions and could leave a dangerous voltage present on earthed parts. With bonding and supplementary bonding, there is less risk of serious electrical shocks in the event that the circuit does not turn off.

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13) What about other Electric Shock Protection?

Aside from electrical grounding, main bonding, supplementary bonding and earthing metallic parts there are other devices that protect against electric shock. The bonding systems and earthing system can offer a great deal of protection but they will not disconnect the electrical circuit that has the fault. 

For disconnection of the electrical circuit, we often need an RCD (residual current device). What is an RCD? An RCD is a protective device that is installed on electrical circuits. The RCD protects people from a flow of electricity passing through their body. It monitors a single or several electrical circuits to check for any electric current leaking to earth. 

It does this by checking the electrical current flow on the LINE and NEUTRAL wire. The electric current should be the same in both and if there is any current leakage the RCD will trip.

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14) Summary

Earthing and Bonding is essential to ensure that there is no electrical potential between conductive parts. Correct bonding and earthing will mean that no fault current will flow through a human body thus preventing shocks. 

Any protective bonding conductor should be installed correctly and labelled as such to ensure that the connection is not removed. Whilst effective earthing and bonding are vital, RCD protection is also recommended in nearly all domestic circumstances. 

Speak with your electrician is you suspect that your metalwork, pipework, and other vital parts in your home are not bonded correctly.

 

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