Engineer Electric Work key terms

The relationship stating that voltage across a conductor equals current through it multiplied by its resistance, written V = I × R, and the basis for calculating any one quantity when the other two are known.

The property of a material that opposes current flow, converting electrical energy to heat, measured in ohms and depending on resistivity, length, and cross-sectional area of the conductor.

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; low values increase current for the same useful power.

Power that oscillates between source and reactive loads such as inductors and capacitors without doing net work, measured in volt-amperes reactive, and needed to sustain magnetic fields in motors and transformers.

The product of root-mean-square voltage and current in an alternating-current circuit, measured in volt-amperes and equal to the vector sum of real and reactive power.

An alternating-current supply arrangement using three voltages of equal magnitude displaced by 120 electrical degrees, which delivers constant power to a balanced load and uses conductors more efficiently than single-phase systems.

The order in which the three phase voltages of a supply reach their positive maximum values, which determines the direction of rotation of three-phase motors and must be verified before paralleling sources.

The reduction in voltage along a conductor or circuit caused by impedance carrying current, calculated from current, conductor resistance and reactance, and limited by code to keep equipment terminal voltage adequate.

Steady-state sinusoidal components of a waveform at integer multiples of the fundamental frequency, produced by nonlinear loads such as rectifiers and variable-speed drives, causing overheating and neutral overloading.

A static device with two or more coupled windings that transfers energy between alternating-current circuits by electromagnetic induction, changing voltage and current levels while preserving frequency and, ideally, power.

The number of turns on a transformer winding divided by the number on another winding, which approximately sets the ratio of voltages and the inverse ratio of currents between those windings.

The brief, high-magnitude current drawn when a transformer is energized, caused by core saturation and lasting from a few cycles to seconds, which must be considered when setting overcurrent protection.

An alternating-current machine in which current induced in the rotor by the rotating stator field produces torque, operating at a speed slightly below synchronous speed and widely used for industrial drives.

The difference between synchronous speed and actual rotor speed of an induction motor, usually expressed as a percentage of synchronous speed, increasing with load and necessary for torque production.

The rotational speed of the magnetic field in an alternating-current machine, equal to 120 times frequency divided by the number of poles, and the speed at which a synchronous machine runs in steady state.

The process of matching voltage magnitude, frequency, phase angle, and phase sequence of a generator or source before connecting it in parallel with an energized system to avoid damaging currents and mechanical stress.

The maximum current a conductor can carry continuously under stated conditions without exceeding its rated temperature, determined from conductor material, size, insulation, ambient temperature, and installation method.

Reducing a conductor's or equipment's tabulated current rating to account for adverse conditions such as elevated ambient temperature, multiple current-carrying conductors in a raceway, or continuous loading.

A load expected to operate at maximum current for three hours or more, which under installation codes generally requires circuit conductors and overcurrent devices sized at 125 percent of the load.

The intentional use of fuses or circuit breakers to automatically interrupt current exceeding a safe value, protecting conductors and equipment from overheating and fault damage while permitting normal starting currents.

A protective relay that operates when current exceeds a set threshold, often with inverse time characteristics, used to detect overloads and short circuits and to trip associated circuit breakers.

The selection of protective device ratings and settings so that the device nearest a fault clears it first, minimizing outage extent and preventing unnecessary tripping of upstream devices.

A scheme that compares currents entering and leaving a protected zone, such as a transformer or busbar, and trips when the difference indicates an internal fault, providing fast and selective clearing.

The intentional connection of exposed conductive parts and the system neutral to earth, together with low-impedance bonding between metalwork, to limit touch voltage and provide a fault current path.

Connecting conductive parts together so they remain at substantially the same potential, preventing dangerous voltage differences between simultaneously accessible metalwork during normal operation or a fault.

A protective device that monitors the vector sum of currents in circuit conductors and trips when a small imbalance indicates current flowing to earth, protecting people against electric shock.

A formal procedure in which energy sources are isolated, locked, and tagged by each worker before work begins, ensuring equipment cannot be re-energized until every lock and tag is removed.

A dangerous release of energy caused by an electric arc between conductors or to earth, producing intense heat, light, pressure, and molten metal, and requiring arc-rated clothing and safe working distances.

A defined distance from exposed energized parts within which only qualified persons may enter, with further restricted and prohibited zones limiting work activities according to voltage and shock risk.

A documented authorization issued for hazardous or high-risk work that records the scope, hazards, isolation points, precautions, and sign-offs, and must be closed out when the job finishes.

A structured process of identifying hazards, estimating the likelihood and severity of harm, and deciding on controls, used before electrical work and reviewed when conditions change.

The ranking of risk controls from most to least effective: eliminating the hazard, substituting it, engineering controls, administrative controls, and finally personal protective equipment.

A computer analysis of a power network that calculates voltage magnitudes, angles, and power flows on each branch for specified generation and demand, used to check voltages and equipment loading.

An analysis calculating prospective fault currents at points in a system, used to select protective devices, verify equipment interrupting ratings, and set relay coordination for safe fault clearing.

The degree to which supply voltage and current waveforms conform to expected sinusoidal characteristics, covering sags, swells, transients, harmonics, and flicker that can disturb or damage connected equipment.

A polyphase load in which the impedances of all phases are equal, so phase currents are equal in magnitude and evenly displaced, allowing simplified analysis and minimizing neutral current.

Delivering the same useful output, such as lighting or motor torque, using less electrical energy, achieved through higher-efficiency equipment, better controls, and reduced losses in distribution.

The professional obligation to hold public safety, health, and welfare paramount, practice only within one's competence, report accurately, avoid conflicts of interest, and sign only work one has supervised.

The project process of formally reviewing, approving, and documenting modifications to agreed deliverables, so that cost and schedule impacts are authorized rather than absorbed silently.