Motor Notes & Terms
NEMA Enclosure Classifications
Where the enclosure is intended to be used
- Type 1 - Intended for indoor use primarily to provide a degree of protection against (hand) contact with enclosed equipment. Usually, a low cost enclosure but suitable for clean and dry environments.
- Type 2 - Intended for indoor use primarily to provide a degree of protection against limited amounts of falling dirt and water.
- Type 3 - Intended for outdoor use primarily to provide a degree of protection against windblown dust, rain, and sleet; undamaged by ice which forms on the enclosure.
- Type 3R - Intended for outdoor use primarily to provide a degree of protection against falling rain and sleet; undamaged by ice which forms on the enclosure.
- Type 4 - Intended for indoor use primarily to provide a degree of protection against windblown dust and rain, splashing water, and hose directed water; or damage by ice which forms on the enclosure.
- Type 4X - Intended for indoor or outdoor use primarily to provide a degree of protection against corrosion, windblown dust and rain, splashing water, and hose directed water; undamaged by ice which forms on the enclosure.
- Type 6 - Intended for indoor or outdoors which occasional temporary submersion is encountered.
- Type 6P - Intended for indoor or outdoors which occasional prolonged submersion is encountered. Corrosion protection.
- Type 12 - Intended for indoor use to provide a degree of protection against dust, falling dirt, and dripping non-corrosive liquids.
- Type 13 - Intended for indoor use primarily to provide a degree of protection dust, spraying of water, oil, and non-corrosive coolant.
Explosion Proof Classifications
- Class I Locations - Class I locations are those in which flammable gases or vapors are or may be present in sufficient quantities to produce explosive or flammable mixtures.
- Class I, Division 1 - Class I, Division 1 locations are where hazardous atmospheres may be present during normal operations. It may be present continuously, intermittently, periodically, or during normal repair or maintenance operations, or those areas where a breakdown in processing equipment releases hazardous vapors with the simultaneous failure of electrical equipment.
- Class I, Division 2 - Class I, Division 2 locations are those in which volatile flammable liquids or gases are handled, processed or used. Normally, they will be confined within closed containers or in closed systems from which they can escape only in the case of rupture or deterioration of the containers or systems.
- Class II Locations - Class II locations are those that are hazardous because of the presence of combustible dust.
- Class II, Division 1 - Class II, Division I locations include areas where combustible dust may be in suspension in the air under normal conditions in sufficient quantities to produce explosive or ignitable mixtures (Dust may be emitted into the air continuously, intermittently or periodically), or where failure or malfunction of equipment might cause a hazardous location to exist and provide an ignition source with the simultaneous failure of electrical equipment. Included also are locations in which combustible dust of an electrically conductive nature are present.
- Class II, Division 2 - Class II, Division 2 locations are those in which combustible dust will not normally be in suspension nor will normal operations put dust into suspension, but where accumulation of dust may interfere with heat dissipation from electrical equipment or where accumulations near electrical equipment may be ignited.
Hazardous Location Groups
- Group A - Atmospheres containing acetylene
- Group B - Atmospheres containing hydrogen, gases or vapors of equivalent hazards such as manufactured gases
- Group C - Atmospheres containing ethyl ether vapors, ethylene or cyclopropane
- Group D - Atmospheres containing gasoline, hexane, naptha, benzene, butane, propane, alcohol, acetone, benzol, lacquer solvent vapors or natural gas
- Group E - Atmospheres containing metal dust, including aluminum, magnesium and their commercial alloys, and other metals of similarly hazardous characteristics
- Group F - Atmospheres containing carbon black, coal, or coke dust
- Group G - Atmospheres containing flour, starch or grain dusts
- Explosion-Proof Enclosure - A totally enclosed enclosure, which is constructed to withstand an explosion of a specified gas, vapor or dust which, may occur within it. Should such an explosion occur, the enclosure would prevent the ignition or explosion of the gas or vapor which may surround the motor enclosure.
- Hertz (HZ) - One cycle per second (as in 60 Hz which is 60 cycles per second).
- Horsepower (HP) - The measure of rate of work. One horsepower is equivalent to lifting 33,000 pounds to a height of one foot in one minute. The horsepower of a motor is expressed as a function of torque and speed. For motors the following approximate formula may be used: HP = (T x RPM)/5250 where HP = horsepower, T = torque (in. lb. ft.), and RPM = revolutions per minute.
- Inverter - An electronic device that converts fixed frequency and fixed voltages to variable frequency and voltage. Enables the user to electrically adjust the speed of an AC motor.
- Open Drip Proof Enclosure - An open motor in which the ventilating openings are so constructed that drops of liquid or solid particles falling on it, at any angle not greater than 15 degrees from the vertical, cannot enter either directly or by striking and running along a horizontal or inwardly inclined surface.
- Phase - Indicates the space relationships of windings and changing values of the recurring cycles of AC voltages and currents. Due to the positioning (or the phase relationship) of the windings, the various voltages and currents will not be similar in all aspects at any given instant. Each winding will lead or lag another in position. Each voltage will lead or lag another voltage in time. Each current will lead or lag another current in time. The most common power supplies are either single- or three-phase (with 120 electrical degrees between the three- phases).
- Poles - In an AC motor, refers to the number of magnetic poles in the stator winding. The number of
poles determines the motor's speed. In a DC motor, refers to the number of magnetic poles in the motor. They create the magnetic field in which the armature operates (speed is not determined by the number of poles).
- Totally-Enclosed Fan-Cooled Enclosure - Provides for exterior cooling by means of a fan integral with the machine, but external to the enclosed parts.
- Totally-Enclosed Non-Ventilated Enclosure - Has no provisions for external cooling of the enclosed parts. The motor is cooled by heat radiation from the exterior surfaces to the surrounding atmosphere.
- Variable Torque - A multi-speed motor used on loads with torque requirements, which vary with speed as with some centrifugal pumps and blowers. The horsepower varies as the square of the speed.
- Voltage - The force that causes a current to flow in an electrical circuit. Analogous to pressure in hydraulics, voltage is often referred to as electrical pressure. The voltage of a motor is usually determined by the supply to which it is attached. NEMA requires that motor be able to carry its rated horsepower at nameplate voltage plus or minus 10% although not necessarily at the rated temperature rise.