ESAA Intermediate Level Exam key terms

The relationship stating that voltage equals current multiplied by resistance (V = I × R). It lets you calculate the third quantity when two are known, and it underlies nearly every circuit troubleshooting measurement you will make.

An AC supply arrangement using three conductors whose voltages are 120 electrical degrees apart. It delivers constant power flow, smaller conductors per kilowatt, and rotating fields that start and run induction motors without auxiliary windings.

The ratio of real power (watts) to apparent power (volt-amperes) in an AC circuit. A value below one means reactive current is present, increasing conductor and transformer loading without producing useful work, which is why utilities may penalize low values.

Power that oscillates between a source and a reactive load such as a motor winding or capacitor, measured in volt-amperes reactive. It does no net work but is needed to build magnetic fields, and it is the component that drives power factor below unity.

A group of capacitors connected to a bus to supply reactive power locally. It reduces the reactive current drawn from the utility, raises power factor, and relieves transformer loading, but must be switched in steps to avoid overcorrection.

The reduction in voltage along a conductor caused by its impedance carrying current. Excessive drop at motor terminals causes overheating, poor starting torque, and nuisance trips, so feeder sizing considers both ampacity and length.

The potential difference measured between any two phase conductors of a three-phase system. It is the value normally stated on motor nameplates and drive input ratings, and it equals line-to-neutral voltage multiplied by the square root of three.

The order in which the three supply voltages reach their peak values. Reversing any two conductors reverses rotation, which reverses the direction of a three-phase motor, making rotation checks essential before connecting driven equipment.

The ratio of primary to secondary winding turns, which sets the ratio of primary to secondary voltage. It also inversely determines current ratio, so a step-down transformer raises available secondary current while lowering voltage.

An AC motor in which current is induced in the rotor by the rotating stator field, so no brushes or slip rings are needed. It is the workhorse of industry because it is rugged, inexpensive, and available in standard frame sizes.

The rotational speed of the stator magnetic field, calculated as 120 times frequency divided by the number of poles. A four-pole motor on 60 Hz has a synchronous speed of 1800 rpm and runs slightly slower under load.

The difference between synchronous speed and actual rotor speed, usually expressed as a percentage of synchronous speed. Slip increases with load and is the mechanism by which an induction motor develops torque.

The current an induction motor draws at rated voltage with its shaft held stationary. It is typically five to eight times full-load current and is the figure used to size overload protection and evaluate starting methods.

A multiplier on a motor's nameplate horsepower indicating how much continuous overload it can carry under stated conditions. A 1.15 service factor allows 15 percent extra load, but only when voltage, temperature, and altitude limits are met.

A letter designation (commonly B, F, or H) defining the maximum allowable winding temperature for a motor. It governs how much thermal margin exists, and running a Class B motor at Class F temperatures shortens winding life substantially.

A contactor arrangement that connects a motor directly to full supply voltage at start. It is simple and cheap but produces the highest inrush current, so it suits smaller motors or supplies with ample capacity.

A protective device that trips when motor current exceeds a set level for a set time, modeling the thermal damage curve of the motor. It protects against sustained overloads, not short circuits, and must be coordinated with upstream fuses.

An electronic controller that rectifies incoming AC to DC and inverts it back to adjustable-frequency, adjustable-voltage AC. Varying frequency changes motor speed, which allows energy savings on pumps and fans and controlled acceleration.

The relationship a drive maintains between output voltage and output frequency to keep motor magnetic flux constant. Too low a ratio weakens torque; too high saturates the iron and overheats the motor.

The switching rate of the transistors inside a drive, typically several kilohertz. Higher settings produce smoother current and quieter motors but increase switching losses and common-mode currents that stress motor insulation and bearings.

Voltage or current at integer multiples of the fundamental frequency, generated by nonlinear loads such as drive rectifiers. It heats transformers and capacitors, trips breakers, and is summarized by a total harmonic distortion index.

The voltage doubling effect that occurs when a drive's fast switching pulses travel down a long motor cable and reflect at the motor terminals. On long leads it can exceed insulation ratings, so filters or inverter-duty motors are used.

A programmed time over which a drive reduces output frequency when stopping. If set too short, the motor regenerates energy into the drive's DC bus and causes an overvoltage trip, so braking resistors or longer ramps are needed.

The internal direct-current link between a drive's rectifier and inverter sections, smoothed by capacitors. Its voltage rises during regeneration and falls during heavy acceleration, making bus measurement a key diagnostic step.

A temperature sensor made of two dissimilar metals joined at a measuring junction, producing a small voltage proportional to temperature difference. It is rugged and wide-ranging but needs cold-junction compensation and shielded extension wire.

A resistance temperature detector, usually platinum, whose resistance rises predictably with temperature. It is more stable and accurate than a thermocouple at moderate temperatures but requires lead-wire compensation and a stable excitation current.

An analog signaling standard in which 4 mA represents the zero or live-zero value and 20 mA the full-scale value. The offset allows detection of broken wires, since a failed loop reads below 4 mA rather than a valid zero.

The DC supply, typically 24 volts, that energizes a two-wire transmitter over the same pair of wires carrying its 4-20 mA signal. Understanding where the supply lives is essential when tracing a dead or erratic measurement.

A digital communication method superimposed on a 4-20 mA signal, allowing configuration and diagnostics without interrupting the analog value. It requires a minimum loop resistance and a communicator or asset management tool.

The correction applied to a thermocouple reading for the temperature of its connection terminals. Without it, the measured voltage reflects the difference between hot and cold junctions rather than the process temperature alone.

An industrial computer with rugged I/O, a deterministic scan cycle, and a programming environment for controlling machinery. It reads inputs, executes ladder or structured logic, and updates outputs repeatedly in a fixed sequence.

The repeating sequence in which a controller reads inputs, solves the program, and writes outputs. Scan time affects response to fast events, so short pulses may be missed unless latched by hardware or interrupt routines.

A graphical programming language drawn as rungs between power rails, with contacts and coils mirroring relay circuits. It remains the most common controller language because electricians can read it intuitively.

A controller input channel that reports only two states, on or off, from a switch, limit, or proximity sensor. It is wired as sinking or sourcing, and mismatching that arrangement is a common cause of inputs that never change state.

A channel that converts a continuous signal, such as 4-20 mA or 0-10 V, into a scaled numeric value in the controller. Its resolution and scaling determine how small a process change the program can detect.

A dangerous release of energy caused by an electrical fault through air, producing intense heat, pressure, and molten metal. It is the reason for energized-work permits, arc-rated clothing, and incident energy labels on equipment.

The thermal energy per unit area that would reach a worker at a given distance during an arc flash, expressed in calories per square centimeter. It determines the arc rating of protective clothing required for a task.

Defined distances around energized equipment that restrict who may enter. The arc flash boundary marks where incident energy equals the threshold for second-degree burns, while shock boundaries depend on voltage.

A procedure for isolating energy sources with locks and tags before maintenance, ensuring equipment cannot be re-energized. It requires verifying absence of voltage and addressing stored energy such as capacitors and springs.

The practice of verifying a conductor is de-energized with a proven, properly rated tester immediately before contact. The tester itself must be checked on a known live source both before and after the test.

Unintended current flowing from a live conductor to earth or to grounded metal. It is detected by sensing the imbalance between outgoing and returning current, and it is the target of equipment and personnel protective devices.

The intentional connection of metal parts to establish electrical continuity and a low-impedance fault path. Bonding lets fault current trip protective devices quickly and keeps touch voltages between surfaces low.

The maximum fault current a piece of equipment can withstand without damage or hazard. The rating must meet or exceed the available fault current at its installation point, a check often missed after service upgrades.

The maximum continuous current a conductor can carry under stated conditions without exceeding its temperature rating. It depends on material, insulation, ambient temperature, and the number of current-carrying conductors bundled together.

A measurement of each motor phase winding's resistance, compared phase to phase and to prior records. Large imbalance or a change over time signals loose connections, shorted turns, or damaged windings before failure occurs.

An insulation resistance measurement made with an elevated DC voltage, checking for moisture, contamination, or degradation. Readings are trended rather than judged against one number, because temperature and humidity strongly affect results.

Using accelerometer measurements and spectral analysis to identify mechanical faults such as imbalance, misalignment, and bearing defects. Specific frequency patterns point to specific causes, allowing repair before damage becomes catastrophic.

Infrared imaging of energized equipment to find abnormal heating from loose connections, overloaded conductors, or failing components. It is performed under load, since a lightly loaded circuit may reveal no temperature difference.

A structured method for tracing a failure back to its underlying cause rather than the surface symptom. Techniques such as the five-whys or fault trees help prevent repeat failures instead of repeatedly replacing the same part.