I.S. 10101 / ET101 Wiring Rules key terms

The stated boundary describing which electrical installations, voltages and locations the standard applies to, and which installations or equipment are excluded from its requirements.

The core safety objectives an installation must satisfy: protection against shock, thermal effects, overcurrent, and safe operation, before any detailed rule is applied.

A person who has the training, knowledge and experience needed to carry out the work safely and to recognise and avoid the hazards involved.

A person who is adequately advised or supervised by a competent person to enable them to avoid hazards that electricity can create.

Protection against direct contact, achieved by insulating live parts, using barriers or enclosures, or placing live parts out of reach.

Protection against indirect contact, achieved by earthing and automatic disconnection, or by double insulation, extra-low voltage, or equivalent measures.

A protective measure in which a fault causes the protective device to open the circuit within a required time, removing dangerous touch voltage from exposed metalwork.

The total impedance of the path taken by fault current from the point of fault through the protective conductor and earth back to the source, which must be low enough to trip the device.

The maximum permitted duration for which a protective device may allow fault current to flow before opening the circuit, set by the standard for the circuit voltage and type.

A protective device that continuously compares current in the live and neutral conductors and trips when the imbalance, indicating earth leakage, exceeds its rated residual operating current.

The rated value of earth leakage current at which a residual current device is designed to operate, commonly 30 mA, 100 mA or 300 mA.

Supplementary protection, typically by a 30 mA residual current device or supplementary equipotential bonding, used in addition to and never instead of basic and fault protection.

A current exceeding the rated value of a conductor or device, arising either from overload, where the circuit is healthy but overburdened, or from short circuit.

An operating condition in which a circuit carries current above its rating but the circuit remains electrically sound, so protection must operate before harmful heating occurs.

The current that flows when a low-impedance path bypasses the normal load, typically very large and limited only by the impedance of the source and circuit conductors.

The current that would flow at a given point if a short circuit of negligible impedance occurred there, used to select devices with adequate breaking capacity.

The maximum fault current a protective device can safely interrupt without damage to itself or danger to its surroundings.

Selection of protective devices so that the device nearest a fault operates first, limiting the outage, while conductors and devices remain protected against overload and fault current.

Deliberate time or current grading between protective devices so that only the device closest to a fault trips, leaving upstream devices closed.

A device installed to limit transient overvoltages from lightning or switching and divert surge current, protecting equipment and insulation in the installation.

The maximum current a conductor can carry continuously under stated conditions without its temperature exceeding the rated limit for its insulation.

A multiplier applied to a tabulated current rating to account for installation conditions such as ambient temperature, grouping of circuits, or thermal insulation.

The presence of several circuits or cables run close together, which restricts heat dissipation and requires derating of each cable's current-carrying capacity.

The reduction in voltage along a circuit caused by conductor impedance under load, which must stay within permitted limits so connected equipment operates correctly.

The measured area of a conductor's metal, usually in square millimetres, which determines its current-carrying capacity and resistance.

A conductor provided for safety purposes, such as earthing exposed conductive parts or bonding, and not intended to carry load current in normal service.

Connection of the installation's exposed conductive parts and the supply neutral point, where required, to the general mass of earth to limit touch voltage.

The way the supply is earthed, such as a separate earth connection, a combined neutral and earth, or an installation earth electrode, which determines the protective measures permitted.

A buried conductor or metal element in contact with the ground that provides an electrical connection to earth for earthing or bonding purposes.

Connecting together conductive parts so they sit at substantially the same potential, preventing dangerous voltage differences between them.

Local bonding of exposed and extraneous conductive parts in a location, used to reduce touch voltage where automatic disconnection alone may not give adequate protection.

The terminal or bar that connects the earthing conductor, circuit protective conductors and main bonding conductors together at the origin of the installation.

Cutting off supply from all live conductors of an installation or circuit for safety, with the means secured against inadvertent reconnection.

A device that isolates all live conductors of a circuit or installation, clearly identified and capable of being locked in the off position.

A procedure or device that secures an isolating switch in the open position, often with a padlock and warning label, so supply cannot be restored accidentally.

A physical guard or housing that prevents contact with live parts and, for enclosures, also protects equipment against external influences.

A two-digit classification of an enclosure's protection against ingress of solid objects and water, such as IP44 for splash-proof equipment.

An installation in a location with increased risk, such as a bathroom, construction site or agricultural building, where additional or modified requirements apply.

A defined region around a bath, shower or similar fitting within which strict rules govern the equipment permitted and the protection required.

The overall process of inspection, testing and certification carried out to confirm a new or altered installation complies with the standard before it is put into service.

Routine inspection and testing of an existing installation at defined intervals to confirm it remains safe and compliant, resulting in a condition report.

A test confirming that protective and bonding conductors form an unbroken low-resistance path, usually performed with a low-resistance ohmmeter.

A test applying a raised DC voltage between live conductors and earth to confirm insulation is sound and free of damaging leakage paths.

A formal document recording the results of verification and declaring that the installation, as far as inspected and tested, complies with the standard.