Retrospective Design: Why are electrical installations non-compliant?

September 25, 2017

Old wiring installation

When the initial installation was installed it would have been designed to the standards of the day. It has always been the requirement that appropriate documentation identifying and detailing the factors and conclusions of the procedure must be provided.

However, as changes are made to the installation, this documentation is rarely updated and maintained. Although condition reports will have been produced at various intervals confirming that the disconnection times within BS 7671 have been achieved, they do not determine that the initial installation’s fundamental design requirements regarding the voltage drop requirements etc have been maintained.

This can have disastrous consequences and possibly result in non-payment of insurance claims etc.


“As the installation increases in size then the voltage drops within the installation change. An increase in load in one section may adversely affect the conditions in another section causing motors to stall, lighting to fail and other equipment to malfunction.”


To understand in detail why so many installations are now non-compliant it is necessary to look back at how they have evolved, how changes to the installation have been managed and if/how design work has been undertaken at the time.

At the handover of a completed new installation it has been confirmed by inspection and testing that the design and the installation are in compliance with both BS 7671 and the EAW Regulations. The operation and maintenance of the installation then becomes the responsibility of the “Duty Holder”.


Completion and handover of original installation

Upon completion of an electrical installation, BS 7671 requires that an Electrical Installation Certificate be completed and a copy given to the client for their retention.

The Certificate usually requires three signatures for a larger type of installation and possibly one signature for smaller type installations such as domestic and small commercial installations.

Each signature represents the responsibilities for that which the signatory has undertaken i.e. the design of the installation, the installing of the component parts of the installation and the verification of the installation. On smaller installations the responsibility of the design installation may be carried by one specific individual. The certificate to be completed is usually referred to as a Single Signature Electrical Installation Certificate.

Once the installation has been completed and verified that it has been designed and installed to the requirements of BS 7671, the responsibility of the upkeep of the installation then becomes the client’s responsibility.

The Electricity At Work (EAW) Regulations place a “duty of care” upon the person responsible for the upkeep of the installation, usually referred to as the “Duty Holder”. They also place duties on employers, employees and self-employed personnel to design, install, operate and maintain electrical equipment in a safe condition.

The EAW memorandum (available online) requires that: All systems (installations) shall at all times be of such construction as to prevent, so far as is reasonably practicable, danger and... As may be necessary to prevent danger, all systems (installations) shall be maintained so as to prevent, so far as is reasonably practicable, such danger.


The original installation

“The installation, upon completion is in compliance with the appropriate regulations. However, minimum sized cabling may have been used.”

The term “such construction” covers several factors, one being that all installed equipment should be suitable for the voltage ranges that it will be connected to i.e. within the parameters laid down by the manufacturer. The voltages available at the terminals of all equipment will have been calculated by the designer in the early stages of the design process.

However, it is usual in most cases to install the minimum size cables provided that conformity with the appropriate regulations has been achieved. This generally happens due to financial constraints placed upon designers in conjunction with the people who are responsible for the placing of tenders etc.

Installing the minimum size cable has potential to cause problems in the future.


As time passes

“As time passes, additions and alterations are commonly made to existing installations. When this happens it is often the case that the design parameters identified and calculated by the original designer will have been compromised.”

Circuits added to or installed at the remote end of a large installation will cause a reduction in the voltage at the incoming distribution board thereby influencing the voltage at the other equipment’s terminals to reduce. This in effect may cause equipment to fail, rotating machinery to stall and high bay lights may not function correctly etc.

The consequences of the items described above may result in "danger". The installation, therefore, may not comply with the requirements of BS 7671 and, therefore, the requirements of the EAW Regulations may have been breached with possible disastrous consequences.

It is a requirement to verify the voltage drops within the installation to satisfy the requirements contained within BS 7671. It is also a requirement to identify any departures from the original design or from the requirements of BS 7671.


Testing installation voltage drops

Although there are two methods of confirming that the installation voltage drops are compliant they are extremely complex, time consuming and it is difficult to confirm the validity of the obtained results.


Disconnection times

It must be kept in mind that BS 7671 requires that the installation be periodically tested to confirm so far as is reasonably practicable that the installation is in a satisfactory condition for continued use. This involves a detailed examination (inspection) supplemented by testing to confirm that the disconnection times have been satisfied.


Identifiying departure from design

On larger installations it is possible that distribution cable ratings may now be overloaded due to additions and alterations etc. and the previously acceptable voltage drops at board and equipment terminals may now be inadequate and may not be sufficient to provide the safe functioning of equipment etc

By retrospectively designing older installations using ProDesign, we can identify quickly and where necessary rectify any issues relating to the design criteria.

Find out more about how ProDesign can help you manage existing installation here.

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