CAA NZ AME Electrical key terms

A low-resistance conductor joining two metallic aircraft structures so they sit at the same electrical potential, preventing sparking and static build-up between them.

A measurement, usually with a four-wire milliohm meter, confirming that the resistance between bonded structure points is within the limits set in the maintenance manual.

The deliberate interconnection of aircraft structure, components and plumbing to form a continuous conductive path, providing fault current return and lightning or static protection.

A small high-resistance wick fitted to trailing edges that bleeds accumulated static charge into the air, reducing radio interference and the risk of corona discharge.

Instrument applying a high DC test voltage to measure insulation resistance of a circuit or winding, used to detect moisture, contamination or breakdown before returning equipment to service.

The opposition offered by cable insulation or winding insulation to leakage current, measured in megohms and compared against a minimum value stated by the manufacturer.

A check, typically with a low-voltage ohmmeter, confirming that a conductor or connection provides an unbroken low-resistance path where one is intended.

The maximum electric stress an insulating material can withstand without breakdown, usually expressed as kilovolts per millimetre and verified by a high-potential test.

An overvoltage test applying a specified AC or DC voltage to insulation to prove it can withstand operating and transient stress without flashover or damage.

A wire end fitting attached by controlled mechanical deformation using a calibrated crimping tool, giving a gastight joint that must meet pull-out and resistance requirements.

Removal of insulation from a conductor end to a specified length without nicking or scoring the strands, since damaged strands reduce current capacity and promote fatigue failure.

A conductor made of many fine wires bundled together, giving flexibility and resistance to vibration fatigue, and requiring correct strand count after termination.

The relationship stating that current through a conductor equals voltage across it divided by resistance; the basis for calculating loads, voltage drop and fault currents.

The principle that the total current entering a junction equals the total current leaving it, used to analyse parallel branches and return paths in aircraft distribution.

The principle that the algebraic sum of voltages around any closed loop is zero, so source voltage equals the sum of the individual voltage drops.

A circuit in which components are connected end to end so the same current flows through each, and total resistance is the sum of individual resistances.

A circuit in which components share the same voltage across common nodes, with total current equal to the sum of branch currents and total resistance lower than any branch.

The reduction in potential along a conductor caused by its resistance carrying current; excessive drop at a load causes dim lamps, slow motors and unreliable avionics operation.

The property of a coil or conductor that opposes any change in current by developing a back EMF, important when switching relays and motor windings.

The ability of two separated conductors to store charge when a potential difference exists between them, measured in farads and used for filtering and suppression.

The total opposition to alternating current from resistance, inductive reactance and capacitive reactance combined, expressed in ohms and dependent on frequency.

A voltage induced in a conductor or coil that opposes the change producing it, seen when a motor spins or when a relay coil is de-energised.

A supply arrangement of three alternating voltages displaced by 120 electrical degrees, giving constant power delivery and rotating fields in induction motors.

An AC generator producing alternating output from a rotating magnetic field, used on aircraft with a rectifier or as a direct AC source for high-power systems.

Electronic unit that regulates generator voltage, monitors output for overvoltage, undervoltage and overfrequency, and controls connection of the generator to the bus.

A hydraulic or mechanical unit maintaining a constant output speed to an alternator despite engine speed changes, so that AC frequency stays within limits.

A unit combining a constant speed drive and an oil-cooled alternator in one housing, commonly used on transport aircraft to produce fixed-frequency AC power.

An AC generation scheme delivering power at a fixed frequency, typically 400 Hz, through a constant speed drive or inverter so frequency-sensitive equipment operates correctly.

An AC generation scheme whose output frequency varies with engine speed; equipment must tolerate the variation or be fed through a converter.

Assembly converting AC bus power to low-voltage DC using a transformer and rectifier bank, supplying DC buses and charging the aircraft battery.

A device converting DC into AC at a controlled frequency and waveform, used to supply AC equipment when engine-driven AC is unavailable, such as on battery power.

A contactor or breaker connecting two or more electrical buses, allowing a failed generator's loads to be supplied by a healthy source and enabling split-bus operation.

A distribution bus wired to supply critical loads such as flight instruments and radios, arranged so it remains powered after loss of a main generator.

A heavy-duty relay connecting the aircraft battery to the DC bus, controlled by the flight crew and opened automatically during certain fault conditions.

A resettable protective device that opens a circuit automatically on overload, and on aircraft must be reset only by approved personnel under defined conditions.

A slow-acting protective device similar to a fuse, used in high-current aircraft feeder circuits to clear sustained overloads that a circuit breaker would not handle.

A diode connected across an inductive load such as a relay coil to provide a path for collapsing current, protecting switching contacts and electronics from induced voltage spikes.

A calculation comparing connected and probable simultaneous electrical loads against available generator capacity, used to justify dispatch and modification approvals.

An approved document specifying which equipment may be inoperative for dispatch under stated conditions, including electrical items with defined operating limitations.

A mandatory instruction issued by the regulator to correct an unsafe condition, requiring inspection or modification within a stated compliance time.

Manufacturer-issued information recommending inspection, modification or part replacement; it becomes mandatory only when made so by an airworthiness directive or operator requirement.

A certification, signed by authorised personnel, stating that maintenance has been completed and the aircraft or component is fit for return to service.

The study of how human capabilities and limitations affect maintenance performance, covering fatigue, complacency, distraction and error management in engineering tasks.

A commonly taught list of twelve human-factor precursors to maintenance error, including fatigue, pressure, distraction, complacency, lack of knowledge and poor communication.

A technician's accurate perception of the current task, environment and aircraft state, enabling anticipation of hazards such as live circuits or unrecorded work.

Selection of conductor cross-section so that normal current, voltage drop and fault heating remain within limits, accounting for bundling, ambient temperature and altitude.

A drawing showing electrical connections between components by function rather than physical location, used for fault-finding and understanding circuit paths.

A simplified drawing using standard symbols to show how a system functions electrically, without representing the physical layout of wires or components.

Alphanumeric code printed along aircraft wire identifying circuit function and segment, enabling correct tracing against the wiring diagram during maintenance.