©Johnstone Supply eCatalog 216

MOTOR DEFINITIONS Electric Motor Terminology

Squirrel Cage Blower (Centrifugal ) — Air moving device consisting of vaned wheel within a housing. Squirrel Cage Winding — A permanently short-circuited winding, usually uninsulated and chiefly used in induction motors, having its conductors uniformly distributed around the periphery and joined by continuous end rings. This secondary circuit is usually called the rotor. Starting Switch, Centrifugal — A centrifugally-operating switch usually used in connection with split-phase and capacitor start motors to open or disconnect the starting winding after the rotor has attained a predetermined speed, and to close or reconnect it prior to the time the rotor comes to rest. Stator — The portion of a motor on which the coils are wound. Stroboscope (Strobe) — A device that can be tuned to the speed of a rotating shaft, making it appear to stand still. The dial reads in RPM so the speed can be instantly noted. Tachometer — Speed measuring device. Temperature Rise — Amount of heat a motor generates above ambient. Thermal Protector — A protective device built into motors which protects them from overheating due to overload or failure to start. Basic types are: Automatic-Reset (Auto): When motor cools, the protector automatically restores power. Automatic reset protective devices should not be used where unexpected restarting would be hazardous. Manual-Reset-(Man): Are equipped with external buttons that must be pushed to restore power to the motor. Recommended where unexpected restarting could be hazardous, such as saws, conveyors, etc. Torque — A force which produces or tends to produce rotation or twist. Common units of measurement of torque are pound feet, pound inches, ounce feet, and ounce inches. Breakdown: The maximum torque which a motor will develop with rated voltage applied at rated frequency without an abrupt drop in speed. Locked Rotor: The minimum torque which a motor will develop at standstill, with rated voltage applied at rated frequency. Also called starting torque or breakaway. Pull Up: The minimum torque developed by an alternating current motor during the period of acceleration from standstill to the speed at which breakdown torque occurs with rated voltage applied at rated frequency. Class I, Division 2 locations are those in which flammable volatile liquids or flammable gases are handled, processed, or used. In these locations, the liquid or gas will normally be confined within closed containers or systems from which they can escape only in the event of accidental breakdown or abnormal operations. The National Eletric Code requires the use of an explosion proof motor for Division 2 locations. The motors selected should be designed for a hazardous location. All motors designed for one hazardous location may not necessarily suitable for use in another. For example: Class I, Group D motors are not suitable for use in Class II, Group G location, unless both conditions are listed on the Underwriters Laboratory label on the motor. Hazardous atmospheres of both a gaseous and dusty nature are classified by the National Electrical Code as follows: Class I Group A atmospheres containing acetylene. Group B atmospheres containing hydrogen or gases or vapors of equivalent hazards, such as manufactured gas. Group C atmospheres containing ethyl-ether vapor. Group D atmospheres containing gasoline, petroleum, naptha, alcohol, acetone, lacquer-solvent vapors and natural gas. Class II Group E atmospheres containing metal dust. Group F atmospheres containing carbon-black, coal or coke dust. Group G atmospheres containing grain dust. Explosion proof equipment is not generally available for Class I, Group A or B locations, and it is necessary to isolate motors from the hazardous area. Explosive Atmosphere Classes

Types of Motors — Classified by operating characteristics and type of power required. Capacitor Start Motor: A type of single phase induction motor that has a capacitor in series with the starting winding only during the starting operation. This type of motor has high locked rotor torque with low amp draw, high breakdown torques used on hard starting applications such as compressors, positive displacement pumps, conveyors, etc. Capacitor Start - Capacitor Run: Performance and applications are similar to capacitor start induction run, the capacitor run enables operation at lower current demand and improved efficiency. Used on larger single phase HP ratings. Permanent Split Capacitor (PSC) : Single phase induction motor which has a capacitor continuously in the auxiliary winding. Unlike the split phase or capacitor start type motors there is no centrifugal switch to disconnect the auxiliary winding. This type motor has low starting torque and is best suited for direct drive applications such as fans, blowers, etc. PSC motors are much more efficient than shaded pole. Shaded Pole Motor (SP): A special type of single phase induction motor that utilizes a copper shading coil to provide the necessary displacement for starting. Low starting torque, typically used in direct drive fans, blowers, etc. Split-Phase Motor: The most common type of single phase induction motor. Equipped with a starting winding displaced in magnetic position from, and connected in parallel with the main winding. Generally, this motor has low to moderate locked rotor torque with high locked rotor amps, high breakdown torques, and is used on belt drive blowers, fans, pumps, etc. Three-Phase: These operate on three phase power (3-power lines) dependent upon designs can yield high starting and breakdown torques. They are more efficient than single phase, and larger HP ratings can be furnished. Found in all larger sizes. Direct Current (DC): Require direct current supply and primarily used for adjustable speed drive applications or motor vehicles. Universal Motor: One that can be operated on either AC or DC brush type. Used primarily in high speed applications such as drills, saws, etc. UL — Underwriters Laboratory, an independent organization that sets safety standards for motors and other electrical equipment. Volt — A unit of electrical potential or pressure. Watt — A unit of electrical power, directly converted to work, the product of voltage and amperage. 746 watts are equal to one horsepower. Work — The transfer of energy from one object to another, measured in force multiplied by distance, or foot pounds.

EXPLOSION PROOF

( 1) Class I

(2) Class I Group D & Class II Groups F & G

Frame Size

Group D Only

143T–145T 182T–184T 213T–215T 254T–256T 284T–286T 324T–326T 364T–365T 404T–405T 444T–445T

X X X X X X X X X

X X X X X X X X

X (1) 143T through 445T frame Class I, Group D only. Code T2A motors to be used only in applications with ignition temperatures 280°C or above. (2) Motors meet UL frame limiting temperatures as indicated by code stamped on UL plate. Code T3B will be used as standard on all explosion proof motors. Maximum frame temperature indicated by T3B is 165°C. This is achieved by use of temperature limiting thermostats within the motor. Overload heaters are sill required in the control, for motor and circuit protection. Thermostat leads are identified as P1 and P2. National Electric Code and Underwriters Laboratories require connection of P1 and P2 into the control circuit of a manual reset starter. (3) Use of UL listed devices does not necessarily make an installation conform to the National Electric Code or local codes. Consult Chapter 5 of the National Electric Code local building codes, OSHA requirements and insurance company inspectors for detailed information as to proper procedures.

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