Glossary of Terms
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Glossary of Terms


Adjustable Speed Drive (ASD) and Variable Speed Drive (VSD): Describes equipment used to control the speed of machinery. Where process conditions call for adjustment of flow from a fan or a pump, varying the speed of the drive may reduce energy consumption compared with other techniques for flow control. ASD allows speeds to be selected from several different pre-set ranges, whereas VSD allows the output speed to be changed without steps over a range. Both types can be purely mechanical, electromechanical, hydraulic, or electronic.

Actuator: A device that creates mechanical motion by converting various forms of energy to rotating or linear mechanical energy.

Affinity Laws: They predict how capacity, head and horsepower are affected by changes in the centrifugal pump impeller diameter or shaft speed.

Air Over (AO): Motors typically intended for fan or blower service; the motor is mounted in the air stream for cooling.

Alternating Current (AC): The current flow in the circuit that continuously alternates back and forth. It does this 60 times per second with 60 Hz power.

Ambient Temperature (AMB): The air temperature surrounding the motor.

Ampere (Amp): The amount of electrical current flowing in an electrical circuit.

A.N.S.I. Standard: The American National Standards Institute is a private nonprofit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States.

Armature: The rotating center part of a brush type direct current (DC) motor that comprise of the core, the winding, the commutator, and the shaft.


Base Plate: The foundation on which the pump or motor is mounted.

Bearings: Supports the rotating shaft and allows it to turn with a minimum amount of friction. There are two common types:

  • Sleeve: Common in residential motors and in blower applications where low noise levels are important.
  • Ball: Common in industrial and agricultural motors. 

B.E.P.: The best efficiency point. It is the point where the power coming out of the pump (water horsepower) is the closest to the power coming into the pump (break horsepower) from the driver. This is also the point where there is no radial deflection of the shaft caused by unequal hydraulic forces acting on the impeller.

B.H.P.: Break horsepower. The actual amount of horsepower being consumed by the pump as measured on a pony brake or dynamometer.

Blast Cooled: A term used to describe a motor having an external fan and cooling case that forces cooling air over the motor. Similar to totally enclosed fan cooled.

Bonderize: A process in which zinc phosphate is applied to the motor shaft to help the shaft resist corrosion.

British Thermal Unit (BTU): A measurement of how much energy an air conditioner uses to remove heat from indoor air. BTU typically shows how much heat an air conditioner can remove within one hour. 12,000 BTUS equals 1 ton air conditioning.

Brush: Current conducting material in a DC motor, usually graphite, or a combination of graphite and other materials. The brush rides on the commutator of a motor and forms an electrical connection between the armature and the power source.


Capacitor (or condenser): A device that stores electrical energy. Used on single phase motors.

Capacitor Start, Induction Run Motor: Provides high starting and break-down torque, medium starting current. Used on hard starting applications such as compressors, positive displacement pumps, farm equipment, etc.

Capacitor Start, Capacitor Run Motor: Provides a higher efficiency than Induction Run motors. Generally used in higher HP single phase ratings.

Centrifugal Pump: Moves liquid with centrifugal force.

CFM: Cubic Feet per Minute of air which the fan or blower is moving.

CHP: Combined heat and power.

Clockwise/Counter-Clockwise Rotation (CW/CCW): CW means clockwise rotation viewing the motor from the Shaft end; CCW means counter clockwise rotation.

Closed Control System (CCS): A system used to regulate a process using feedback control. This system responds to actual system conditions with a range of responses.

Commutator: The part of a DC motor armature that causes the electrical current to be switched to various armature windings. Properly sequenced switching creates the motor torque. The commutator also provides the means to transmit the electrical current to the moving armature through the brushes that ride on the commutator.

Continuity: A term used to describe a circuit that is complete, or is able to pass electric current.

Coupling: Used to connect the pump to the driver. It transmits torque and compensates for axial growth.

Cycling (tripping): An occurence when a motor overload interrupts power to the motor due to excessive heat rise.


Direct Current (DC): A current that flows in one direction only and is substantially constant in value.

Direct Torque Control: A VFD method that controls the torque of an AC electric motor.

Disaster Bushing: Used in A.P.I. glands to support the shaft in the event of a bearing failure, or to prevent a product from rushing to atmosphere after a seal failure.

Duty Cycle: The relationship between operating time and the resting time of an electric motor.

  • Continuous Duty: The operation of loads for over one hour.
  • Intermittent Duty: The operation during alternate periods of load and rest.

Dynamic Balancing: Identifies and corrects mass distribution in order to minimize vibration.


Efficiency: The ratio or comparison of power output to power input.

Enclosure: Term used to describe the motor body; the main types are:

  • ODP: Open Drip Proof, housing has openings in end shields and shell to allow air to cool the motor. Normally used in "clean" applications.
  • TEFC: Totally Enclosed Fan Cooled, housing has no openings. Motor is cooled by an external fan on the non-drive end of the motor shaft. Ideal for dirty or damp locations.
  • TENV: Totally Enclosed Non-Ventilated. Not equipped with an external cooling fan; depends on convection air for cooling.
  • TEAO: Totally Enclosed Air Over. Air flow from the driven or external device provides cooling air flow of the motor.

Encoder: A device that converts motion to an electrical signal that can be read by a control device in a motion control system, such as a counter or PLC.

End Bell / End Shield: The plates at each end of the motor.

End Play: This term refers to the in and out movement the rotor has in the motor. Excessive end play can result in problems such as fan blades hitting the fan guards or vibration. No end play can result in a tight motor.

Explosion Proof: The enclosure’s ability to prevent an internal spark or explosion from causing an external blast.


Field: The stationary part of a DC motor, commonly consisting of permanent magnets. Sometimes used also to describe the stator of an AC motor.

Frame: The external motor body; a frame size indicates certain measurements of the motor and shaft, such as shaft diameter and height from ground.

Free Air: The blower or fan blade operates at free air when there are no effective restrictions to air flow at the outlet or inlet.

Frequency: An expression of how often a complete cycle occurs. Cycles per second describe how many complete cycles occur in a given time increment. Hertz (hz) has been adopted to describe cycles per second so that time as well as number of cycles is specified. The standard power supply in the U.S. is 60hz.

Frett (or fretting): Damage or grooving caused by the removal of the protective oxide that is formed on most corrosion resistant metals.

Full Load Amperes (FLA): Amps drawn by a motor when operating at rated load, voltage, and frequency.

Full Load Torque: The torque a motor produces at its rated horsepower and full-load speed.


Gearless Mill Drive (GMD): A system consisting of a ringmotor and its associated equipment such as transformers and control systems.

General Purpose Motor: It is designed with standard operating characteristics and mechanical construction for use under usual service conditions. Has a service factor rating.

Generator: Any machine that converts mechanical energy into electrical energy.

Grounding: The connection of a motor to an earth ground to reduce the possibility of electrical shock.


Heating Degree Days: Each degree that the average temperature is below 65 degrees Fahrenheit produces one heating degree day.

Hertz: Frequency in cycles per second of an AC power supply. The U.S. operates on 60 hertz (H).

Hi Pot (High Potential): This is a motor test used to detect conditions where electrical conductors (i.e., lead wires, magnet wire) may have come in contact with the non-electrical parts of the motor (i.e., stator laminations, shell).

Horsepower (HP): The rating of a motor’s ability to do work.

HP= watts output / 746

HP= (RPM x Torque in ounce-inches) / 1,000,000.

One HP= 746 watts.

HVACR: Acronym for Heating, Ventilation, Air Conditioning, and Refrigeration.


Inch-Ounce: A measure of torque (twist). One inch-ounce is equal to one ounce of force applied 1” out away from center line of the shaft.

International Electrotechnical Commission (IEC): The worldwide organization that promotes international unification of standards or norms. Its formal decisions on technical matters express, as nearly as possible, an international consensus.

Impedance: The total opposition in an electric circuit to the flow of an alternating current. Expressed in ohms.

Impeller: Attaches to the end of the shaft to impart energy to the fluid being pumped.

Induction Motor: The simplest electric motor, it consists of a wound stator and rotor. The magnetic field in the stator winding creates an electromagnetic induction for the rotor, which rotates and produces torque.

Insulation: In motors, classified by maximum allowable operating temperature. NEMA Classifications include:
Class A=105C, Class B=130C, Class F=155C and Class H=180C.

Integral: Whole number. Used to describe horsepowers of motors over one horsepower.

Integral Horsepower Motor: A motor rated one horsepower or larger at 1800RPM. By NEMA definitions, this is any motor having a three digit frame, for example 143T.

Inverter: An electrical device for converting DC into AC power.


Jacket: Usually refers to the heating/ cooling jacket surrounding the stuffing box on some pumps.


Kilowatt: A unit of power equal to 1000 watts and approximately equal to 1.34 horsepower.


Leads: The connection wires brought out from the internal winding to make the external connections. Star and delta are the standard methods for three phase motors.

Load Factor: The work required of a motor to drive attached equipment. Expressed in horsepower or torque at a certain motor speed.

Lug: Mounting bracket extending from the motor shell, usually three or four.


Mechanical Duty: Cooling by means of a fan inside or outside the motor housing.

Metric: A decimal system of measurement.

Microfarad (MFD): Capacitor rating

Motor: A machine that converts electrical energy into mechanical energy.


NEC (National Electric Code): A national code written for the purpose of safeguarding persons and property from the hazards arising from the improper use of electricity. It is sponsored by the National Fire Protection Institute and used by insurance inspectors and by many government bodies regulating building codes.

NEMA (National Electrical Manufacturers Association): A non-profit trade organization, supported by manufacturers of electrical apparatus and supplies in the United States. NEMA standards for motors cover frame sizes and dimensions, horsepower ratings, service factors, temperature rises, and performance characteristics.


O.E.M.: Original Equipment Manufacturer.

O.D. (Outside Diameter): The dimension of a round object measured across the outer edges at locations 180 degrees apart.

Ohms Law: The basic relationship between the voltage, current, and resistance in a circuit. Voltage = Current x Resistance.

Open Circuit: A break in an electrical circuit that prevents normal current flow.

OSHA: Occupational and Safety Health Act.

Output Shaft: The shaft of a speed reducer assembly that is connected to the load. This may also be called the drive shaft or the slow speed shaft.

Overhung load: Is the perpendicular force pushing against the side of an output shaft. This force is either from a weight hanging on the output shaft or from a sprocket, pulley or gear being used on the shaft.

Overload Protector: A temperature-detecting device built into the motor that disconnects the motor from the power source if the temperature rise becomes excessive.


Parallel: Electrical components that are connected in a way so that the flow of electricity can take multiple, or parallel, paths through the circuit.

Permanent Split Capacitor (PSC): (Single Phase) Performance and applications similar to shaded pole motors, but more efficient, with lower line current and higher horsepower capabilities.

Permawick: The oil-soaked cellulose fiber material that is packed into the motor end plates for sleeve-bearing lubrication. These fibers are made of 80-90% ground wood fibers and 10-20% sulfite fibers.

Phase: The number of individual voltages applied to an AC motor. A single-phase motor has one voltage in the shape of a sine wave applied to it. A three-phase motor has three individual voltages applied to it. The three phases are at 120 degrees with respect to each other so that peaks of voltage occur at even time intervals to balance the power received and delivered by the motor throughout its 360 degrees of rotation.

Phase-Shifting Transformer (quadratic booster): A specialized type of transformer used on 3-phase power grids (AC) to balance the active (real) and reactive power in the system and thereby preventing the loss of lines through physical overloading.

Phasor Measurement Units (PMUs): Monitoring devices installed at critical nodes in a power network to collect data on power flow.

Photovotaic Cells (PV): Device that converts radiation from the sun directly into DC electricity.

Pitch: Referring to the angle of the wings on a fan blade.

Poles: Magnetic devices set up inside the motor by the placement and connection of the windings. Divide the number of poles into 7200 to determine the motor's normal speed. For example, 7200 divided by 2 poles equals 3600RPM.

Power Capacity: In terms of generation, the capacity of a power plant is the maximum power that installation is capable of producing.

Power Factor: A measure of an electrical circuit’s effectiveness on a scale of zero (lowest) to 1 (highest).

PSC: Permanent-Split Capacitor.

Pulley: A wheel on an axle that is designed to support movement and change of direction of a cable or belt along its circumference.


Rectifier: An electrical device used to convert AC into DC.

Relay: A device have two separate circuits, it is constructed so that a small current in one of the circuits controls a large current in the other circuit. A motor starting relay opens or closes the starting circuit under predetermined electrical conditions in the main circuit (run winding).

Resilient Mounting Ring: This is a rubber ring that is part of the end plate assembly on some motors. Its primary function is to provide the customer a means of mounting the motor to a base or bracket on the equipment. This ring isolates vibration.

Resistance: This is the measure of a conductor’s ability to conduct current. Resistance is measured in ohms. One ohm of resistance will allow one amp to flow through a conductor that has a voltage of one volt impressed on it.

Resistor: A device that resists the flow of electrical current for the purpose of operation, protection or control. There are two types of resistors-fixed and variable. A fixed resistor has a fixed value of ohms while a variable resistor is adjustable.

Rewind: AC and DC motors employ an insulated, current-carrying coil essential to their operation. The method of motor rewinding is traditionally done by hand by a highly skilled technician that involves removing the old coil, winding the new coil and varnishing.

Ringmotor (or wrap-around motor): A very large synchronous motor. The poles of the motor are directly flanged on the driven equipment.

Rotation: The direction in which a shaft turns is either clockwise (CW) or counterclockwise (CCW). When specifying rotation, also state if viewed from the shaft end or the opposite shaft end of the motor. 

Rotor: The rotating member of a motor. It is constructed from stacked iron laminations. There are channels in the stack that are filled with molten aluminum. These aluminum bars get currents induced in them from the winding magnetic flux. The currents produce their own magnetic flux. This rotor interacts with the winding flux to produce rotation. The shaft is securely pressed on the rotor.

RPM: Shaft Revolutions Per Minute.


SIL (Safety Integrity Level): A rating given of a system to indicate the level of risk associated with it. It is a measure of its ability to perform safely and, in the event of failure, to fail safely.

Series Wound: Noting a commutator motor in which the field current and armature circuit are connected in a series.

Service Factor: Pertains to self-cooled motors. A measurement which states the percent horsepower the motor can carry beyond its nameplate rating and remain self-cooled. A service factor of 1.3 has a 30% horsepower margin built into the motor.

Shaded Pole Motor: (Single Phase) Motor has low starting torque, low cost. Usually used in direct-drive fans and small blowers, and in small gearmotors.

Sheave: A grooved wheel or pulley.

Short Circuit: A fault or defect in a winding causing part of the normal electrical circuit to be bypassed, frequently resulting in overheating of the winding and burnout.

Shunt Wound: Noting a motor or generator that has the field circuit connected in parallel with the armature winding.

Sleeve Bearing:  A sleeve style bushing used to support a rotor in a motor. This style provides quiet motor operation as compared to ball bearings.

Slip: A term describing the difference between the rotor speed and the speed of the motor’s rotating magnetic field. Rotors always drag behind the speed of a magnetic field.

Slot Insulation: Also called Slot Liner. The insulation material used in the stator slots to protect the motor windings from scraping the laminations. It also provides winding protection against grounding to the laminations.

Special Purpose Motor: Machines designed for a specific application. Developed when an OEM has refined the operating characteristics or construction features of the motor. Does not have standard operating characteristics or standard mechanical features.

Split Phase (or more specifically Split-Phase start-induction run): (Single Phase) Motor has moderate starting torque, high breakdown torque. Used on easy-starting equipment, such as belt-driven fans and blowers, grinders, centrifugal pumps, gearmotors, etc. 

Squirrel Cage Blower/Centrifugal Blower/Forward Curve Blower: Air-moving devices consisting of a wheel made of many fins. The wheel is contained within a housing.

Stack: Thickness of a motor stator.

Starting Torque: The amount of turning force produced by a motor as it begins to turn from a standstill. Also called locked rotor torque.

Static Balancing: Balancing without rotation.

Stator: The fixed part of an AC motor, stack of iron laminations on which the coils are wound.

Strobe: An RPM measuring device that flashes light pulses at a rotating shaft. The pulses are adjusted until an optical illusion of the shaft standing still is obtained. At this point, the RPM reading is taken.

Submersible Motor: A motor whose housing is designed so that the motor can run under water; completely submerged. These are commonly used in water pumps.

Surge: To suddenly increase as an electric current or voltage.

Synchronous Motor: A motor that runs at synchronous speed without slip.


Tachometer: RPM measuring device.

Temperature Rise: Amount of heat a motor generates above the ambient temperature.

Thermal Protector: A device, sensitive to current and heat, which protects the motor against overheating due to overload or failure to start. Basic types include automatic rest, manual reset and resistance temperature detectors.

Thermostat: A temperature-sensing unit that is mounted on the stator winding to monitor temperature in order to avoid overheaing. Two leads from the device must be connected to control circuit, which initiates corrective action. The customer must specify if the thermostats are to be normally closed or normally open.

Thermocouple: A pair of dissimilar conductors joined to produce a thermoelectric effect and used to accurately determine temperature. Thermocouples are used in laboratory testing of motors to determine the internal temperature of the motor winding.

Three-Phase Power: A form of electricity used to supply heavy loads.

Torque: The twisting or turning force produced by a shaft. Usually expressed in inch-pounds or inch-ounces for fractional and sub-fractional HP motors.

    Starting Torque: Force produced by a motor as it begins to turn from standstill and accelerate (sometimes called locked rotor torque).
    Full-Load Torque: The force produced by a motor running at rated full-load speed at rated horsepower.
    Breakdown Torque: the maximum torque a motor will develop under increasing load conditions without an abrupt drop in speed and power. Sometimes called pull-out torque.
    Pull-Up Torque: The minimum torque delivered by a motor between zero and the rated RPM, equal to the maximum load a motor can accelerate to rated RPM.


Underwriters Laboratories (UL): An independent U.S. agency that establishes safety standards for manufacturers to follow.


Vector Control (also called field oriented control- FOC): A variable frequency drive (VFD) control method which controls 3-phase AC electric motor output by means of two controllable VFD inverter output variables.

Vibration Analysis: A test conducted to identify trouble spots that could cause problems (such as resonance and fatigue).

Voltage: The measure of electromotive force that causes current to flow in a circuit.


Watt: The measure of mechanical power available from a motor. One horsepower is equal to 746 watts.

Winding: Typically refers to the process of wrapping coils of copper wire around a core, usually of steel. In an AC induction motor, the primary winding is a stator consisting of wire coils inserted into slots within steel laminations. The secondary winding of an AC induction motor is usually not a winding at all, but rather a cast rotor assembly. In a permanent magnet DC motor, the winding is the rotating armature.


Contact Square One Electric with any questions about service or terminology.

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