SG PPE Electrical key terms

The relationship stating that current through a conductor is directly proportional to voltage across it and inversely proportional to resistance, expressed as V = I × R.

The electrical potential difference between two points, measured in volts (V), that drives current through a circuit.

The rate of flow of electric charge through a conductor, measured in amperes (A).

The opposition to the flow of electric current in a material, measured in ohms (Ω).

The total opposition to alternating current flow in a circuit, combining resistance and reactance, measured in ohms (Ω).

The ratio of real power (watts) to apparent power (volt-amperes) in an AC circuit, indicating how effectively electrical power is used.

Electric current that periodically reverses direction, typically in a sinusoidal waveform, as supplied by the mains.

Electric current that flows consistently in one direction, such as from a battery or rectified supply.

The number of complete cycles of an alternating current per second, measured in hertz (Hz).

A conductor that is energised in normal service and carries current to the load, typically coloured brown in single-phase systems.

A conductor connected to the star point of the supply and intended to carry current under normal conditions, typically coloured blue.

A protective conductor that connects exposed conductive parts to the earth, typically coloured green-and-yellow, to provide a path for fault current.

An individual conductor within a cable, consisting of stranded or solid metal, insulated from other cores.

Non-conductive material surrounding a conductor to prevent electric shock and short circuits between conductors.

The outer protective covering of a cable that provides mechanical and environmental protection to the insulated cores inside.

A automatic switch that opens a circuit to interrupt fault current, protecting against overload and short circuit, and can be reset.

A protective device containing a wire or strip that melts and breaks the circuit when current exceeds a rated value, requiring replacement after operation.

A protective device that disconnects a circuit when it detects a difference between live and neutral currents, indicating earth leakage.

A condition where current exceeds the rated value of a circuit or device for a prolonged period, causing overheating but not necessarily a short circuit.

An unintended low-resistance connection between live conductors or between live and earth, causing excessive current flow.

A fault where a live conductor comes into contact with earth or an exposed conductive part, allowing fault current to flow to earth.

The connection of exposed conductive parts and the supply system to the general mass of earth to ensure fault current can flow and protective devices operate.

The connection of conductive parts to ensure electrical continuity and equal potential, reducing the risk of electric shock.

Connecting together all exposed and extraneous conductive parts to maintain them at substantially the same potential, preventing dangerous voltage differences.

A metal rod or plate buried in the ground to provide a direct electrical connection to the earth.

The total impedance of the path taken by fault current from the point of fault through the earth and back to the supply, determining disconnection time.

The maximum current that would flow if a short circuit occurred at a given point in an installation, used to select protective devices.

Contact of a person with a live conductor that is normally energised, such as touching a bare live wire.

Contact of a person with an exposed conductive part that has become live under fault conditions, such as a metal casing.

Measures that prevent contact with live parts under normal conditions, such as insulation, barriers, and enclosures.

Measures that protect against electric shock when a fault occurs, such as earthing and automatic disconnection of supply.

The process of disconnecting an electrical supply from an installation or circuit to ensure it is safe to work on, often using a lock-off device.

A safety procedure that uses locks and tags to ensure electrical equipment remains de-energised during maintenance or repair work.

A step-by-step method to ensure a circuit is dead before work, including identifying, isolating, locking off, proving dead, and proving the tester.

The process of using a voltage indicator to confirm that a circuit or conductor is not live before starting work.

A device used to detect the presence of voltage on a conductor or circuit, essential for proving dead during safe isolation.

A test that applies a high DC voltage between conductors and earth to measure the resistance of insulation, verifying it is adequate.

A test that verifies a low-resistance path exists between two points, such as for protective conductors and bonding.

A test that confirms live, neutral, and protective conductors are connected in the correct positions throughout an installation.

Current that flows from a live conductor to earth through an unintended path, such as through a person or faulty insulation.