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ARESCO Technical Bulletin Vol. 1, No.1 June 1998

Have You Ever Wondered What The Motor Nameplate Information Means?

Many people know what "HP" and "Volts" means when they read it on the motor nameplate. Well, we at ARESCO would like to help you understand the other parts of the nameplate that aren't so common. Using the nameplate from our popular TATUNG motor line, we would like to share with you in this Technical Bulletin, just what you need to know to fully understand all the information found on a motor nameplate.

Nameplate Data
The National Electrical Manufacturer's Association (NEMA) specifies that every motor nameplate must show these specific items: Manufacturer's Name; Rated volts and full load amps; Rated frequency & number of phases; Rated full load speed; Rated temperature rise or the insulation system class; Time rating; Rated horsepower; Locked rotor indicating code letter; Service Factor; Efficiency; Frame Size; and Design Code. Additional information will normally appear on most nameplates.

This Technical Bulletin will go over the required nameplate items and many of the optional items that are shown on our Tatung nameplate. The required items will be covered first in the order previously mentioned.

Manufactures Name is self explanatory, however we like to see the name "TATUNG" on our nameplates!

Rated Volts And Full Load Amps. Tatung Motors will operate at a variety of line voltages, the most common being 230 and 460. These motors will operate according to NEMA limits at rated voltage.

Line voltage will fluctuate due to a variety of factors. Therefore, every motor must be designed to handle these voltage variations. Tatung motors can withstand voltage variation of plus or minus 10%, so a 230 Volt motor could operate between approximately 207 to 253 volts. At these extremes, no motor will run at its peak performance, however it will withstand these conditions.

Rated Frequency is the frequency the motor is designed for represented by Hertz (cycles per second). 60 Hertz power is used throughout the United States, Canada, and other parts of the world while 50 Hertz is the standard in the rest of the world. Tatung motors can tolerate a frequency deviation of plus or minus 5%. Most Tatung motors are 3 phase motors because of cost effectiveness.

RPM (Revolutions Per Minute) of a motor is the speed at which the motor will rotate at rated voltage and frequency during full torque. This "full load" speed will normally vary between 87% and 99% of synchronous speed depending on design. This is known as slip.

Synchronous speed is the theoretical speed of a motor based on the rotating magnetic field. This is determined by the following:

S =(120 x F)/P
S = speed in RPM
F = frequency in hertz
P = # of poles in motor

Or, if you know the number of poles in your motor, you can determine the speed by the following chart:

# of Poles
Synchronous Speed
Actual Speed
2
3600
3450
4
1800
1725
6
1200
1140
8
900
850

Insulation. Insulation is crucial in a motor. Tatung insulates its motor to withstand the greatest temperature that occurs at the hottest point within the motor for as long as the temperature normally exists. This is determined by, the ambient temperature, the heat generated at fully loaded conditions (temperature rise), and the thermal capacity of the motor insulation. These materials are classified as A, B, F, and H.
The classes are based on adding the ambient temperature and the operational heat created by the motor. They are shown below.

Class
20,000 Hour Life Temperature
A
105°C
B
130°C
F
155°C
H
180°C

Time rating. Unless otherwise noted Tatung motors will be rated for continuous duty. This will be shown as "CONT" on the nameplate.

Horsepower. Horsepower is determined by the output when the motor is loaded to rated torque at rated speed. These are the standard NEMA ratings:

1
30
300
1250
1 ½
40
350
1500
2
50
400
1750
3
60
450
2000
5
75
500
2250
7 ½
100
600
2500
10
125
700
3000
15
150
800
3500
20
200
900
4000
25
250
1000

When application horsepower requirements fall between two standardized values, the larger size is usually chosen.

The work capacity of a horse was used to define the power of an electric motor. It was determined that a horse could lift 1000 pounds, 33', in one minute. It is the amount of work done in a given amount of time. The formula is:

HP = (Foot #s Per Minute) \ 33,000 -or- HP= (Foot #s per second) \ 550

Torque is the turning or twisting force supplied by a drive to the load, measured in inch pounds or foot-pounds. Torque and horsepower are related as shown:

HP=(Torque X Speed)/Constant

If Torque is given in Ft. Lbs, the constant is 5252

If Torque is given in In. Lbs the constant is 63,025

Locked Rotor Indicating Code Letter. When a motor is started, a large 'inrush' of current is required in order to get a good start. This current is greater than the full load running current. This inrush has been standardized and defined by a series of code letters which group motors based on the amount of inrush in terms of kilovolt amperes. The code letter defines low and high voltage inrush values on dual voltage motors. These values can be used for sizing starters, etc.

Code
KVA/HP
Approx. Mid-Range Value
A
0.00-3.14
1.6
B
3.15-3.54
3.3
C
3.55-3.99
3.8
D
4.00-4.49
4.3
E
4.50-4.99
4.7
F
5.00-5.59
5.3
G
5.60-6.29
5.9
H
6.30-7.09
6.7
J
7.10-7.99
7.5
K
8.00-8.99
8.5
L
9.00-9.99
9.5
M
10.00-11.99
10.6
N
11.20-12.49
11.8
P
12.50-13.99
13.2
R
14.00-15.99
15.0

Using this chart and the job voltage, you can calculate the across the line starting inrush by using the following:

200 Volts LRA = Code letter value x HP x 2.9
230 Volts LRA = Code letter valve x HP x 2.5
460 Volts LRA = Code letter value x HP x 1.25

Motor Service Factor (SF) is a factor that when multiplied by horsepower, gives us the allowable horsepower loading, which may be carried under the conditions specified for the service factor at rated voltage and frequency. This is practical as it gives you some 'fudge' in estimating horsepower needs and actual running horsepower requirements. It also allows for cooler winding temperatures at rated load, protects against intermittent heat rises, and helps to offset low or unbalanced line voltages.

The drawbacks to running in the service factor area is that it will reduce motor speed and efficiency & increase motor temperature. This in turn effects the overall life span of the motor. It is for this reason that you should not run in the SF range continuously. Service factors were established for operations at rated voltage, frequency, ambient and sea level conditions.

Efficiency. Efficiency is the ratio of the power output divided by the power input. The efficiency is reduced by any form of heat, including friction, stator winding loss, rotor loss, core loss (hysteresis and eddy current), etc.

Frame Size. Motor frame size have been standardized with a uniform frame size numbering system. This system was developed by NEMA and specific frame sizes have been assigned to standard motor ratings based on enclosure, horsepower and speed.

NEMA Design Letter. Changes in motor windings and rotor design will alter the performance characteristics of induction motors. To obtain uniformity in application, NEMA has designated specific designs of general purpose motors having specified locked rotor torque, breakdown torque, slip, starting current, or other values. NEMA design letters are A, B, C, and D.

NEMA Design A motors have normal starting torques, but high starting currents. This is useful for applications with brief heavy overloads. Injection molding machines are a good application for this type of motor. Many of the Tatung design B motors can handle Design A requirements!

NEMA Design B motors are the most common. They feature normal starting torque combined with a low starting current. These motors have sufficient locked rotor torques to start a wide variety of industrial applications.

NEMA Design C motors have high starting torques with low starting currents. They are designed for starting heavy loads due to their high locked rotor torques and high full load slip.

NEMA Design D motors have high starting torque and low starting current, however they feature high slip. This reduces power peaks in the event that peak power is encountered, motor slip will increase.

Enclosure Type. Tatung motors are typically supplied in open drip-proof (ODP), totally enclosed fan cooled (TEFC), explosion proof (EXP), totally enclosed non-vent (TENV), totally enclosed chemical duty, and totally enclosed wash down.

Manufacturer's Identification Numbers. The model, date, & serial number are supplied to aid in identification.

Bearing Part Numbers. The bearing part numbers are included if replacement bearings need to be obtained.

Connection Diagrams. This diagram is to aid a qualified electrician in the wiring of a Tatung motor.