Red Seal Industrial Electrician key terms

A formal procedure in which energy sources are isolated, locked and tagged before work begins, so equipment cannot be re-energized while a worker is servicing or repairing it.

The amount of thermal energy per unit area that would reach a worker at a stated distance from an arcing fault, used to select protective clothing and set arc flash boundaries.

A shock-protection distance around exposed energized parts that unqualified persons may not cross unless escorted; qualified workers crossing it still need suitable personal protective equipment.

A written authorization required before justified work on or near energized equipment; it records the hazards, the safeguards to be used and the signatures of those approving the work.

A protection method that limits the electrical energy and surface temperature of circuits in a hazardous location to levels too low to ignite the surrounding flammable atmosphere, usually using barriers or galvanic isolators.

The model installation code published by CSA Group as CSA C22.1 and adopted with local amendments by Canadian jurisdictions, setting minimum requirements for the safe installation of electrical equipment.

The ratio of the maximum demand of a system, or part of it, to the total connected load, used when sizing feeders, services and associated equipment.

The maximum current, in amperes, that a conductor can carry continuously under the stated conditions of use without exceeding its rated conductor temperature.

The relationship stating that the current through a resistor equals the voltage across it divided by its resistance, commonly written as I equals V divided by R.

The ratio of real power in watts to apparent power in volt-amperes in an AC circuit; a value of one means voltage and current rise and fall together.

The total opposition a circuit presents to alternating current, combining resistance and reactance into a single value measured in ohms and denoted by Z.

The effective value of an alternating current or voltage; it produces the same heating effect in a resistor as an equal direct current or voltage would.

The loss of voltage along conductors caused by current flowing through their resistance and reactance, usually expressed in volts or as a percentage of the source voltage.

A conductor installed to ensure electrical continuity between metal parts so they remain at substantially the same potential and form part of the effective ground-fault current path.

A device that compares current in the ungrounded and grounded conductors and trips when a small difference shows current is leaking to earth through a person or equipment.

The percentage of a raceway's internal cross-sectional area occupied by conductors, limited by code to control heat build-up and allow conductors to be pulled without damage.

The number of primary winding turns divided by the number of secondary turns; in an ideal transformer this equals the ratio of primary voltage to secondary voltage.

A three-phase transformer arrangement with a delta primary and a wye secondary, providing a neutral point for grounding and line-to-neutral loads along with a 30-degree phase shift.

The maximum current a system can deliver at a given point during a short circuit, determined by source impedance, transformer size and the impedance of upstream conductors.

The speed at which the magnetic field of an AC machine rotates, calculated as 120 times the supply frequency divided by the number of poles.

The difference between the synchronous speed of the rotating magnetic field and the actual rotor speed of an induction motor, usually stated as a percentage of synchronous speed.

A test that applies a steady direct voltage between a winding or conductor and ground and measures the resulting resistance, revealing moisture, contamination or degraded insulation.

A motor starter that applies full supply voltage directly to the motor through a contactor, together with overload protection and usually a disconnecting means.

A protective device that senses motor current and opens the control circuit when sustained current above the motor rating would otherwise overheat the motor windings.

An electronic controller that changes the frequency and voltage supplied to an AC motor so that its speed and torque can be matched to the process requirement.

A switching technique that turns a DC supply on and off rapidly with a varying duty cycle so the average output approximates a desired waveform such as a sine wave.

An industrial digital computer that reads input signals, repeatedly executes a stored control program and drives output devices to operate machines and processes.

The continuously repeated sequence in which a PLC reads the status of all inputs, solves the user program from memory and then updates all of its outputs.

A graphical programming language in which contacts, coils and function blocks are arranged in rungs between power rails to imitate traditional relay control circuits.

A PLC module that converts a continuous voltage or current signal into a digital number that the processor can scale and use in its control program.

An analog signalling standard in which a transmitter varies loop current from 4 mA at zero to 20 mA at full scale; a reading near 0 mA indicates a broken wire or lost supply.

A closed-loop control method that sums three responses to the error between setpoint and measured value: proportional action, integral action and derivative action.

A temperature sensor formed by joining two dissimilar metals; the junction produces a small voltage that increases as the temperature difference between junction and reference changes.

A temperature sensor, commonly a platinum element, whose electrical resistance rises in a predictable way with temperature, giving stable and accurate measurement.

A circuit of diodes or thyristors that converts alternating current into direct current, usually followed by filtering to smooth the resulting output.

A two-terminal semiconductor device that allows current to flow easily in one direction and blocks it in the other, used for rectification and surge protection.

A system that keeps supplying power to a load from batteries or another stored energy source when the normal supply fails or fluctuates outside acceptable limits.