Every electrical installation, shall, during erection and on completion, before being put into service, be inspected and tested to verify, so far as is reasonably practicable, that the requirements of the Regulations have been met.

Fixed equipment or appliances are more difficult to inspect and test because of the nature of their attachment to the building fabric and their connection to the fixed wiring of an installation. However given the prominent nature of some of these equipment types, they should receive a full combined inspection and test at relevant intervals.

All fixed electrical installations and equipment should be verified in accordance with BS 7671.

Periodic inspection and testing is necessary because all electrical installations deteriorate due to a number of factors such as damage, wear, tear, corrosion, excessive electrical loading, ageing and environmental influences.

Periodic inspection and testing of every electrical installation must be carried out in order to determine, as far as reasonably practicable, whether the installation is in a satisfactory condition for continued service. Wherever possible, the documentation arising from the initial certification and any previous periodic inspection and testing shall be taken into account. Where no previous documentation is available, investigation of the electrical installation shall be undertaken prior to carrying out the periodic inspection and testing.

Guidance on the initial frequency and subsequent frequencies at which periodic inspections should be performed are given in the IET’s Guidance Note: 3 (GN3) Inspection and Testing. It also provides information on the necessary competence of those carrying out the inspections and any testing.

A number of factors need to be considered when determining the time interval between periodic inspection and testing of an electrical installation. These include the type of installation and equipment, its use and operation, any known maintenance and the external influences to which it is subjected.

GN3 recommends a maximum initial period between inspection and testing of 3 years for industrial installations and 5 years for offices / laboratories, with an annual routine check of all installations. These periods can be amended by the Authorising Engineer after a risk assessment of the electrical installation (specified on their letter of appointment) has been completed.