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Contact us

Emergency information

0800 6783 105

General contact enquiries

0800 096 3080

Information for electrical installers

Please contact us to discuss your requirements  if you require one of the following:

  • a new electricity connection;
  • you are making significant changes to an existing; installation - for example, adding electrical equipment or altering earthing arrangements. 
We will undertake, on request, a small number of tasks on behalf of customers and their electrical installers. The tasks as listed below are primarily for domestic connections, but may also be applied to small commercial installations that utilise whole current metering.
 

De-energising and re-energising the customer's installation

In some cases it is necessary for the incoming electrical supply to be de-energised to allow an electrical installer to safely work on a customer's wiring and equipment safely.  You can arrange for the supply to be de-energised and re-energised by calling the customer's Electricity Supplier.  The Electricity Supplier's name, address and telephone number is shown on the customer's electricity bill. If you have any difficulty arranging for this to be carried out please contact us.

Provision of PME (Protective Multiple Earthing)

We provide PME (protective multiple earthing) facilities as standard at the vast majority of new electricity connections.  In some cases we can also install a PME earthing terminal at existing non-PME installations, although this does depend on the design of our electricity system and on the type of installation.

Installation of an Isolation Switch

We can install a 2 pole or 4 pole isolation switch that may be operated by the customer’s electrical installer, allowing them to de-energise and re-energise the customers’ installation themselves.

Replacement of meter box door

Where an external meter box is fitted, this is owned (and should be maintained) by the customer. If a meter box door has been damaged and needs replacement, we may make a charge for this work.

Fixed charges apply to each of the above standard tasks. For a list of our current charges please click here.

Connection characteristics

The electrical characteristics of an installation have to be considered when designing a new - or modifying an existing - electrical system. The following information is often required:

System voltage

Low voltage connections (up to 1000V)

The following standard voltages apply:

  • Single phase connections; 230V (phase-neutral)
  • Two and three phase connections; 230V (phase-neutral) and 400V (phase-phase)
  • Split phase connections; 230V (phase-neutral) and 460V (phase-phase)

The voltage should remain within +10% and –6% of these figures.

High voltage connections (above 1000V)

Large commercial or industrial installations are often connected at high voltage. A number of different standard voltages are in use within Western Power Distribution’s area, including:

  • 6600V (phase-phase)
  • 11000V (phase-phase)
  • 33000V (phase-phase)
  • 66000V (phase-phase)
  • 132000V (phase-phase)

The voltage should remain within ± 6% of the nominal connection voltage, with the exception of 132000V connections where the tolerance is ± 10%.

Number of phases

Low voltage connections (up to 1000V)

The number of phases provided at low voltage connections will vary depending on the capacity of connection and the nature of our electricity network. The following arrangements are typical: 

  • Single phase
  • Two phase (also known as two phase – four wire)
  • Split phase (also known as two phase – three wire)
  • Three phase

Where more than one phase is provided load must be balanced, as far as possible, between each of the phases.

High voltage connections (above 1000V)

Three phases are provided at high voltage connections.

System frequency

The statutory limit for frequency is 50 Hertz  ± 1%.

Maximum prospective short circuit current

The maximum prospective short circuit current is used to determine the short circuit rating requirement of electrical equipment.

Low voltage connections (up to 1000V)

The following values can be assumed at low voltage connections:

  • Single phase connection; 16kA
  • Two phase, split phase or three phase connection; 25kA

High voltage connections (above 1000V)

We can provide maximum prospective short circuit current information for high voltage connections upon request.

Maximum earth fault loop impedance

The maximum earth fault loop impedance is used to calculate the available earth fault current within an installation connected at low voltage (below 1000V).

The following values are typical for low voltage installations:

Earthing type Maximum earth fault loop impedance

Protective multiple earthing (TN-C-S)

0.35 ohms*

Cable sheath earth / Separate continuous earth wire (TN-S)

0.8 ohms*

Direct earth (TT)

Dependent on resistance of the customer’s earth electrode. Values exceeding 100 ohms can apply.

 

* These values are sometimes exceeded where the connection is derived from a long overhead line network or from a small pole mounted transformer.

Type and rating of WPD’s fuse or circuit breaker

The type and rating of our fuse or circuit breaker installed at the point of connection can be provided on request. In some cases it will be necessary for us to carry out a site check, and to de-energise the supply for a short time in order to check the fuse size.

Type of earthing

Low voltage connections (up to 1000V)

The three most common low voltage arrangements are described as follows.      

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 its 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 upon request.

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 upon request.