©Johnstone Supply eCatalog 216

MOTOR DEFINITIONS Electric Motor Terminology

Air Over Motor (AO) — The motor, directly connected to a fan, is kept cool with the stream of moving air. Alternating Current (AC) — The flow of electricity through a conductor that is constantly changing its direction of flow. House current is AC. Ambient (Amb) — The temperature of the air surrounding the motor. Ampere (Amp) — The unit of measurement for rate of current flow, commonly referred to as an “amp”. Armature (Arm) — That part of an electrical machine which includes the main current carrying winding. In direct-current machines, the armature winding is connected to the commutator and the armature is the rotating member. In alternating current machines without commutators, the armature may be either the rotating member or the stationary member. Bearing — Located in the end bell, it supports the shaft and provides for smooth rotation. Sleeve (Slv.): Used where low noise level is important, such as on fans and blower motors. Ball: Used where higher load capacities are required or where relubrication is inconvenient. Unit: Motors with one long sleeve bearing constructed for fan duty only. Binding Post — A threaded terminal for connecting wire to electrical equipment. Also known as a stud. Bracket — Another name for end shield or end bell. BTU — An abbreviation for British Thermal Unit; 12,000 BTU equals 1 ton air conditioning. CW, CCW — Clockwise and counter clockwise rotation when viewing motor from the end indicated by manufacturer. Capacitor (Condenser) — A device which introduces capacitance into an electric circuit. The material which separates the conductors in a capacitor is called the dielectric. Capacitors are usually classified according to this material. For example, there are paper, air, oil and mica capacitors. Conductor — Material that may be used as a carrier of electrical current. Constant Speed Motor — A motor whose speed is constant or substantially constant over the normal range of loads. Current — The flow of an electrical charge through a conductor with the ability to overcome resistance and perform work. Definite Purpose Motor — A motor designed for use on a particular application, with operating characteristics and mechanical construction required by the application. Example: Sump pump motor, oil burner motor. Duty — A requirement of service which defines the degree of regularity of the load. Efficiency — The ratio or comparison of useful power output to the power input. Electric Motor — A machine which transforms electrical energy into mechanical energy. Electrically Reversible Motor — One which can be reversed by changing the external connections. End Bell (End Shield) — Shield at the end of the motor which supports the bearings. Also called end plate. Enclosure (Encl.) — Motor envelope types: Open: An open motor is self-ventilated, having no restriction to ventilation or to the enclosure other than necessitated by mechanical construction. Dripproof (DP): Constructed with ventilation openings so that falling liquid at an angle of 15 degrees from vertical will not enter the motor. T otally Enclosed Non-Ventilated (TENV): Constructed with no openings in brackets or frame. Totally Enclosed Fan Cooled (TEFC): Constructed with no openings in brackets or frame, but includes an external fan with shroud to blow cooling air over motor. Totally Enclosed Air-Over (TEAO): Depends on air flow from driven device for motor cooling. Explosion Proof (XP) — An enclosed motor whose enclosure is designed and constructed to withstand an explosion of a specified gas or vapor which may occur within the motor and to prevent the ignition of this gas or vapor surrounding the machine. Refer to charts for various classes and groups of explosion-proof motors. Frame — The supporting structure for the stator parts. Frame SIZE — Refers to a set of physical dimensions of motors as established by NEMA. These dimensions consist of shaft length, shaft diameter, shaft height and location of base mounting holes. Frequency (Hertz) — The rate at which alternating current changes its direction of flow, usually expressed in terms of cycles per second, usually 60 Hz in USA. Full Load Current (FLA) — The current stamped on nameplate which motor will draw while operating at its designated full load at corresponding voltage.

General Purpose AC Motor — An AC motor built in standard ratings, with standard performance and mechanical construction, offered for general use. Horsepower — Formulas for determining horsepower: HP equals Watts output divided by 746; 746 Watts equals 1 HP. To estimate HP: HP equals torque in oz. inches times rpm divided by one million. Impedance Protected — Motor designed to not burn out in less than 15 days under locked rotor condition, in accordance with UL standards. Induction — The production of an electric current in a conductor by a magnetic field in close proximity to it. Induction Motor — An AC motor in which a primary winding (usually on the stator) is connected to the electrical power source and a secondary circuit (usually the rotor) carries an induced current. Insulation (Ins) — Insulations are classified by their ability to withstand a specified temperature for a specified length of time without deteriorating. The insulation classes normally used and their total allowable temperature (both ambient and rise) are as follows: Class A 105°C (221°F) Class F 155°C (311°F) Class B 130°C (266°F) Class H 180°C (356°F) Locked Rotor Current (LRA) — The measured current taken at rotor stand-still with rated voltage and frequency applied. Mounting — Rigid: Motor solidly fastened to equipment through a metal base welded to the motor shell. Resilient: Motor shell isolated from the base by rubber rings on the end shields. Stud: Motor has bolts extending from front or rear by which it is mounted. Multispeed Motor — One which can be operated at any of two or more definite speeds, each being practically independent of the load. In the case of multi-speed permanent-split capacitor (PSC) and shaded pole motor, the speeds are dependent on the load. NEMA — National Electrical Manufacturers Association. This organization sets electrical and mechanical standards for electric motors. OEM: — Original Equipment Manufacturer. Same as the original part. Ohm — The unit of electrical resistance to the flow of current. Overload Protector — A temperature detecting device built into the motor that disconnects the motor from the power source if the temperature rise becomes excessive. Polyphase — More than one phase, usually three phase. Power — The amount of work which can be done in a unit of time. Power Factor — The ratio of real power (watts) divided by apparent power (volt- amperes). Not to be confused with efficiency (measure of the extent to which power transmission or distribution systems are utilized). Rating — The designated limit of operating characteristics of a machine, apparatus or device based on definite conditions. Load voltage, frequency, and other operating characteristics may be given in the rating. Resistance — The property of an electric circuit or of any object used as part of an electric circuit which determines for a given current the rate at which electric energy is converted into heat or radiant energy, and which has a value such that the product of the resistance and the square of the current gives the rate of conversion of energy. Rotor — The rotating part of most alternating current motors. Service Factor — Number by which the horsepower rating is multiplied to determine the maximum safe load that a motor may be expected to carry continuously. Slot Insulation — Also called Slot Liner. The insulation lining the slot containing the motor windings. Speed (RPM) — The running speed of an AC motor is dependent upon the number of poles and the frequency of the power source. RPM= 120 x Freq. No. Poles No. of Synchronous Normal No. of Synchronous Normal Poles Speed Speed Poles Speed Speed 2 3600 3450 6 1200 1075 4 1800 1725 8 900 825

continued on next page

203

JohnstoneSupply.com