T Frame: Current NA designation identifying AC induction motor frames. (NA has dimension tables which offer standard frame measurements.) Replaced the previous standard U frame in 1965.

Tachometer: A small generator normally used as a rotational speed sensing device. Tachometers are typically attached to the output shaft of DC or AC variable-speed motors requiring close speed regulation. The tachometer feeds its signal to a control which adjusts its output to the DC or AC motor accordingly (called closed loop feedback control).

Temperature: Has direct effect on motor life when considering life expectancy. The following application considerations that affect a motor's operating temperature should be taken into account: 1. Bearings 2. Lubricants 3. Duty Cycle 4. Radial Loading 5. Axial Loading 6. Mounting 7. Enclosure 8. Ambient Temperature 9. Ventilation As a general rule, each 10°C increase in total temperature over the maximum permissible to the motor's insulation system, reduces its life by half. Bearing or gear lubricant life is reduced by half for every 25°F (approximately 14°C) increase in temperature. Heat eventually causes deterioration of most lubricants and seals leading to leakage and increased friction.

Temperature Rise: Some of the electrical energy losses inherent in motors are converted to heat causing some of the motor parts to heat up when the motor is running. The heated parts are at a higher temperature than the air surrounding them which causes a rise above room (ambient) temperature. It is important to match the proper motor and insulation system (NA tp. codes) to the expected ambient temperature. If a motor has been built with greater than 1.0 service factor, then it can operate at a temperature somewhat higher than the motor's rated operating temperature. In all cases, the actual insulation thermal capability usually is higher than the motor's operating temperature to allow for any excessive heat areas. This is called hot spot allowance. Each temperature code has an associated temperature rise which when added to the ambient and hot spot should not exceed the temperature handling of the insulation system.

Temperature Tests: Tests conducted to determine the temperature rise of certain parts of a motor above the ambient temperature, when operating under specific conditions.

TENV - Totally Enclosed Non-Ventilated: Acronym describing a type of motor enclosure, which has no outside air going into it. It is cooled only by convection to the frame, which is usually finned.

Tests Routine: A routine test is a basic test done in the factory to the requirements of NA MG1, paragraph 12.51 and IEEE-112-1978. It includes the following measurements: no load current/watts; winding resistance; and high potential test.

Thermal Protection: A thermal sensing device mounted to the motor to protect it from overheating. This is accomplished by disconnecting the motor phases from the drive in an over temperature condition.

Thermal Protector (inherent): An inherent overheating protective device which is responsive to motor temperature and when properly applied to a motor, protects the motor against dangerous overheating due to overload or failure to start. This protection is available with either manual or automatic reset.

Thermal Resistance (Rth) (°C/watt): An indication of how effectively a unit rids itself of heat; a measure of temperature rise per watts lost. In Pacific Scientific literature, it is the specified value from the motor windings to the ambient, under locked rotor conditions.

Thermal Time Constant (tth) (minutes): The time required for a motor to attain 63.2% of its final temperature for a fixed power input.

Thermocouple – Thermal Detection Device: A temperature detecting device made of two dissimilar metals which generates a voltage as a function of temperature. Thermocouples can be attached to a meter or alarm to detect overheating of motor windings or bearings.

Thermoistor– Thermally Sensitive Resistor: A semiconductor used to measure temperature that can be attached to an alarm or meter to detect motor overheating.

Thermostat: 1. A temperature sensitive pilot duty device mounted on the interior of the motor to protect it from overheating. 2. Units applied directly to the motor's windings which senses winding temperature and may automatically break the circuit in an overheating situation.

Thrust Bearings: Special bearings used to handle higher than normal axial forces exerted on the shaft of the motors as is the case with some fan or pump blade mountings.

Torsional Stiffness: Rotational rigidity of a precision coupling governing the reversal error of a rotary encoder.

Torque: A measure of angular force which produces rotational motion. This force is defined by a linear force multiplied by a radius; e.g. lb-in. Torque is an important parameter of any motion control system. Formula: Torque (lb-ft.) = 5,250 x HP/RPM

Torque Constant (KT = lb-ft./A): An expression of the relationship between input current and output torque. For each ampere of current, a fixed amount of torque is produced.

Torque-to-Inertia Ratio: Defined as the motor's holding torque divided by the inertia of its rotor. The higher the ratio, the higher a motor's maximum acceleration capability will be.

Totally Enclosed Air-to-air Cooled Machine: A totally enclosed machine cooled by circulating internal air through a heat exchanger which in turn, is cooled by circulating external air. Provided with an air-to-air heat exchanger for cooling ventilating air and fan or fans integral with rotor shaft or separate, for circulating external air.

Totally Enclosed Enclosure: A motor enclosure, which prevents free exchange of air between the inside and the outside of the enclosure but is not airtight. Different methods of cooling can be used with this enclosure.

Totally Enclosed Fan-Cooled Enclosure: Provides for exterior cooling by means of a fan(s) 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.

Totally Enclosed Pipe Ventilated Machine: A totally enclosed machine except for openings arranged so inlet and outlet ducts or pipes may be connected to them for the admission and discharge of ventilating air. Air may be circulated by means integral with the machine or by means external to and not a part of the machine. In latter case, these machines shall be known as separately forced-ventilated machines.

Totally-Enclosed Water Air-Cooled Machine: A totally-enclosed machine cooled by circulating air which in turn, is cooled by circulating water. Provided with water-cooled heat exchanger for cooling ventilating air and fan or fans, integral with rotor shaft or separate, for circulating ventilating air.

Transformer: A device which converts electrical power (alternating current) to electrical power of a different voltage. In this device, both primary and secondary windings are usually stationary and are wound on a common magnetic core.

Tube Cooled: A motor in which heat is dissipated by air-to-air heat exchange.

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