This is a common problem experienced by electricians and usually ends up with a higher installation cost in order to carry out the requested electrical work.
If you have decided to have electrical work done such as extra sockets, new lighting points, a new circuit installed to a cooker or shower, or any alterations to electrical circuits in your home, then a registered electrician is required, prior to starting work, to verify that the earthing and protective bonding arrangements are adequate.
After completion of the electrical installation work, the work that has been carried out shall be inspected and tested and a certificate issued. Part of this process is to verify that the earthing and bonding conductors are sized, installed and terminated correctly.
EARTHING AND BONDING EXPLAINED
Earthing is used to protect people from the risk of electric shock. If the earthing arrangements within your electrical installation were defective or inadequate, you could receive an electric shock
from the equipment or appliance metal casing.
The purpose of earthing is to provide a path for electric fault current to flow safely to earth to enable the circuit breaker or fuse to operate.
Bonding is the connection of the incoming metal gas and water pipes to the main installation earthing terminal and is vital for your protection from electric shock.
In a correctly earthed installation, any appliance or equipment developing a fault to the metal casing, will be quickly disconnected by the operation of the fuse or circuit breaker.
SUPPLEMENTARY BONDING EXPLAINED
Supplementary bonding is often found in bathrooms or any room containing a shower. This is to reduce the risk of electric shock where people may touch two separate metal parts, such as radiators and water pipes, should an electrical fault occur in the electrical installation.
In these locations, supplementary protective bonding conductors connect together the circuit protective conductors of electrical equipment e.g. electric shower to hot and cold metal water pipes and any metal radiators or towel rails.
As illustrated, this arrangement was common on installations up to June 30th 2008. With the introduction of new IEE Wiring Regulations BS7671 (2008), after this date the need for supplementary bonding has been reduced, as all electrical installations in rooms containing a bath or shower need to have their circuits additionally protected by a Residual Current Device (RCD).