Type of Earthing

Low Voltage Connections (up to 1000V)

The three most common low voltage arrangements are described below: 
 
Protective Multiple Earthing (PME)

PME, known as TN-C-S within BS7671 (Requirements for Electrical Installations, IEE Wiring Regulations) is the most common form of earthing provided at new installations.  We utilise a single conductor for neutral and earthing functions and provide an earth terminal at the customer’s installation. The customer’s earthing may be connected to this terminal providing all relevant requirements within BS7671 and National Engineering Recommendation G12 are satisfied.

In some cases we are unable to provide PME facilities, either due to the nature of the distribution system or due to the type of installation itself.

Cable Sheath Earthing / Separate Continuous Earth Wire

Cable sheath earthing and separate continuous earth wire arrangements are referred to as TN-S within BS7671 and are often available within older properties, or occasionally where PME facilities are unavailable.  In such cases we utilise separate conductors for neutral and earthing functions and provide an earthing terminal at the customer’s installation. The customer’s earthing may be connected to this terminal providing all relevant requirements within BS7671 are satisfied.

Direct Earthing

Direct earthing, known at TT within BS7671 is common within older properties and is also used where PME cannot be provided. In this case we do not provide an earth terminal and customers installation must include it's own earth electrode system (buried earth rods and conductor).

In older properties direct earthing is often provided by bonding the protective conductors to an incoming metal water pipe, owned and operated by the local water company. Whilst a metal water pipe can act as a reasonable earthing system, it is likely that this will, at some stage in the future, be replaced by plastic piping. For this reason a separate dedicated earthing system should also be provided.

Where direct earthing is employed the installation normally has to be protected by a residual current device (RCD) in order to comply with BS7671.

High Voltage Connections (above 1000V)

Information on earthing at high voltage connections can be provided, on request. New Connections