TP EIMSA key terms

A deliberate conductive connection between exposed metalwork or a circuit point and the general mass of earth, providing a low-impedance path so protective devices operate and touch voltages stay safe.

The conductor that connects exposed conductive parts, extraneous conductive parts and the main earthing terminal to the earth electrode, carrying fault current only during a fault condition.

Connecting all simultaneously accessible metalwork and conductive parts together so they sit at substantially the same potential, preventing dangerous voltage differences between them during a fault.

The resistance measured between an earth electrode and remote earth; it governs how effectively fault current is dispersed into the ground and must be low enough for protective devices to trip.

The potential difference a person could bridge by touching two accessible conductive parts at the same time; it drives the shock current through the body and must stay within safe limits.

A protective device that continuously compares live and neutral currents and trips when their imbalance, representing leakage to earth, exceeds its rated residual operating current within a specified time.

Any current exceeding the rated current of a conductor or device, encompassing both overload current and short-circuit current, and requiring a protective device rated to interrupt it safely.

The current that flows when a low-impedance path bypasses the intended load, typically far above normal operating current and limited only by source impedance and circuit impedance.

The current that would flow at a given point in an installation if a short circuit occurred there, calculated or measured to confirm protective devices can safely interrupt it.

The maximum fault current a protective device can safely interrupt without damage or dangerous arcing, expressed in kiloamperes and compared against the prospective fault current at its location.

Selecting and setting protective devices so that the device nearest a fault operates first, isolating only the affected circuit while upstream devices remain closed and discrimination is preserved.

The total impedance of the fault-current path from the source through the live conductor, the fault and back via the protective conductor, used to verify automatic disconnection within the required time.

The resistance measured between live conductors and earth, or between separate live conductors, with test voltage applied; a low reading indicates degraded or damaged insulation.

A high-voltage withstand test applied to insulation, cables or equipment to prove it can endure elevated stress without breakdown, usually performed during commissioning or after major work.

A verification that live, neutral and protective conductors are connected to the correct terminals throughout a circuit, so switches and protective devices interrupt the intended conductor.

A low-resistance measurement confirming that a conductor or protective bonding path is unbroken end to end, typically made with a low-reading ohmmeter on a de-energized circuit.

The relationship stating that voltage equals current multiplied by resistance in a linear circuit, allowing any one quantity to be calculated when the other two are known.

The ratio of real power in watts to apparent power in volt-amperes in an alternating-current circuit, equal to the cosine of the phase angle between voltage and current.

An alternating-current supply using three sinusoidal voltages displaced by 120 electrical degrees, delivering constant total power and enabling smaller conductors for a given load.

Two ways of connecting three-phase windings or loads: star joins one end of each winding at a neutral point, while delta connects them end to end in a closed loop.

The reduction in voltage along a conductor caused by its impedance carrying load current; excessive drop impairs equipment operation and must be limited by correct conductor sizing.

Reducing a cable's tabulated current-carrying capacity to account for installation conditions such as ambient temperature, grouping, thermal insulation or burial depth.

Selecting conductor cross-sectional area so it carries design current continuously, limits voltage drop, withstands fault energy and coordinates with the chosen protective device.

A mechanical fitting that secures a cable to an enclosure or equipment, provides strain relief and, where required, maintains the earthing and ingress protection of the cable entry.

A rigid support system of metal or non-metallic sections carrying cables in an accessible, ventilated route, often requiring bonding and careful attention to grouping factors.

A two-digit classification, prefixed IP, stating the degree of protection an enclosure gives against solid objects and water, guiding selection for the environment of installation.

Electrical apparatus certified for use in explosive gas or dust atmospheres, marked with its equipment group, category, gas group and temperature class to match the hazardous zone.

The process of dividing a site into zones by the likelihood and duration of a flammable atmosphere, determining which equipment protection concepts and installation rules apply.

A formal procedure isolating energy sources, applying personal locks and warning tags, and proving isolation before work begins so equipment cannot be re-energized unexpectedly.

Confirming a circuit is de-energized by testing with a proven voltage detector on all conductors and phases before touching or applying earthing, never relying on indicators alone.

A documented authorization specifying the work, its hazards, isolations and controls, signed by the responsible person before high-risk activity starts and closed out on completion.

A written description of how a specific task will be carried out safely, covering sequence, personnel, plant, controls and emergency arrangements, usually issued with a risk assessment.

A combination of contactors, overload protection and control circuitry that safely starts, stops and protects a motor, often including reduced-voltage or star-delta starting arrangements.

A protection device that models motor heating with bimetallic elements or electronic sensing and trips the starter when sustained overload current exceeds a set threshold.

The structured process of inspecting, testing, energizing and proving an installation or system against design intent before handover, with results recorded and defects resolved.

A drawing revised to reflect the installation exactly as constructed, including routing, sizes and equipment locations, forming part of the handover documentation for future maintenance.

A structured investigation method, such as five-whys or fishbone analysis, used after a failure to identify the underlying cause rather than only the immediate symptom.

Using an infrared camera to reveal temperature differences in energized equipment, helping locate loose connections, overloaded conductors and failing components before they cause failure.

A portable instrument combining voltage, current and resistance measurement functions, selected by range and function switch and used with leads rated for the category of the circuit.