City & Guilds 2391-51 key terms

Statutory regulations in Great Britain placing duties on those responsible for electrical systems at work to keep them safe, properly maintained and worked on by competent people. Breaching them is a criminal offence.

The British Standard covering the design, erection, inspection and testing of electrical installations. Following it is the accepted way of showing that legal duties, such as those in the Electricity at Work Regulations, have been met.

An IET publication explaining in detail how to inspect, test and certify installations to BS 7671. It is the standard reference for inspection and testing practice and for completing certificates and reports.

The Building Regulations requirement, applying in England and Wales, that electrical installation work in dwellings is safe. Notifiable work must be certified by a registered competent person or by building control.

Someone with enough technical knowledge, skill and experience to carry out the work safely and prevent danger or injury. Their competence must be appropriate to the particular task being done.

A formal sequence of identifying the circuit, switching off, isolating, locking off and proving dead, then confirming the correct circuit was isolated. It protects the worker from electric shock and arc flash.

Using a proven voltage indicator to confirm zero voltage between all live conductors, and between each live conductor and earth, immediately before touching the isolated conductors.

A known voltage source used to check that a voltage indicator is working correctly before and after proving a circuit dead. Some indicators have a built-in self-test instead.

A lock and warning label fitted to an isolator or protective device so that an isolated circuit cannot be re-energised by someone else while work is in progress.

A formal written document authorising specific work under stated safety conditions. It is used for high-risk tasks such as live working or work on complex or hazardous installations.

Scheduled inspection and testing of an existing installation at intervals during its life, to assess its condition and compliance with BS 7671. The findings are recorded in an Electrical Installation Condition Report.

The agreed description of which parts of an installation will be inspected and tested and what will be left out, recorded so readers know exactly what the report does and does not cover.

Inspecting and testing a representative selection of the installation rather than every item, chosen to give reasonable confidence in the condition of the whole. Any parts not sampled must be recorded as limitations.

A careful examination of the installation, without dismantling beyond what is needed, to find damage, deterioration, overheating, incorrect identification, poor workmanship and departures from BS 7671.

A departure from BS 7671 or another applicable standard found during inspection. It must be recorded as an observation and classified according to the risk it presents.

The decline in condition of installation parts through ageing, wear, corrosion, heat or damage, such as cracked insulation or loose connections, which increases the chance of fault or danger.

Inspection and testing of a new installation, or of new work, carried out before it is put into service, to confirm that it matches its design and complies with BS 7671.

The certificate issued after initial verification of a new installation or major alteration, declaring that the work has been designed, constructed, inspected and tested in accordance with BS 7671.

A certificate used for small additions or alterations that do not add a new circuit, covering the design, construction, inspection and testing of that particular piece of work.

The purpose and coverage of the report, agreed with the client before work starts, including the extent, limitations, sampling and any special requirements such as a change of occupancy.

Measuring the resistance of protective, bonding and circuit conductors to show they are continuous and correctly connected. Results are compared with expected values calculated from conductor size and length.

The measured resistance of a circuit's line conductor plus its circuit protective conductor, taken with the supply isolated. It is added to the external loop impedance to give the earth fault loop impedance.

A test of a ring final circuit using end-to-end resistance readings of line, neutral and protective conductors, then a cross-connected reading. The cross-connected value should be roughly a quarter of the end-to-end line-to-neutral value.

Confirming that line, neutral and protective conductors are connected to the correct terminals throughout, so that switches and single-pole devices are in the line conductor and earthing remains effective.

A dead test applying a DC voltage, usually 500 V for 230/400 V circuits, between live conductors and earth and between live conductors, to confirm the insulation is sound. Results must meet the minimum values in BS 7671.

The total impedance of the path taken by fault current from the point of fault, through the protective conductor and back to the supply source. It determines whether the protective device disconnects within the required time.

The impedance of the fault path outside the installation, measured at the origin with the main switch off. It is used together with a circuit's R1+R2 to calculate Zs.

The current that would flow if a short circuit or earth fault occurred at a particular point, measured or calculated at the origin. It is used to check that protective devices and equipment can withstand it.

Using an RCD tester to confirm that a residual current device trips within the required time at its rated residual operating current and at five times that current.

Operating switches, isolators, RCD test buttons, interlocks, emergency lighting and similar equipment to confirm they work as intended as part of the inspection and testing process.

The observation code for a danger present with risk of injury, where immediate remedial action is required and the installation, or the affected part, must be made safe or isolated straight away.

The observation code for a potentially dangerous condition: a defect that could become dangerous and that needs urgent remedial action.

The observation code for an improvement recommended: a departure or non-compliance that is not dangerous but would improve safety if it were put right.

A code used where a problem has been found but cannot be fully assessed without further investigation, for example where part of the installation is hidden or badly deteriorated.

The findings from the inspection and testing, each written up with its location and given a classification code. They form the main body of the condition report and drive the recommendations.

The report produced after a periodic inspection, recording the extent, limitations, test results and observations, with an overall assessment and the date by which the next inspection is due.

The overall assessment on a condition report: satisfactory where no C1 or C2 observations are recorded, and unsatisfactory where any C1 or C2, or an unresolved further investigation, is present.

The form, part of a certificate or condition report, on which measured results such as continuity, insulation resistance, Zs, prospective fault current and RCD operating times are recorded circuit by circuit.