Thermal Unit Selection on an Approximate Basis—Based on Horsepower and Voltage
Thermal units selected using approximate full-load currents from the table titled Use This Table Only When the Motor Full-Load Current Is Not Known will provide a trip current between 101% and 125% of full-load current for many 4-pole, single speed, normal torque, 60 Hz motors. Since full-load current rating of different makes and types of motors vary widely, these selections might not be suitable.
Thermal units should be selected on the basis of motor nameplate full-load current and service factor. Thermal unit sizes originally selected on an approximate basis should always be rechecked and corrected at the time of installation if required.
How to use the table titled Use This Table Only When the Motor Full-Load Current Is Not Known:
-
Locate the motor horsepower and voltage.
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Determine the approximate full-load current from the table Use This Table Only When the Motor Full-Load Current Is Not Known.
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Use the approximate full-load current in place of actual nameplate full-load current and follow the selection procedure in Procedure for Thermal Unit Selection.
Use This Table Only When the Motor Full-Load Current Is Not Known
|
Motor |
Motor Full-Load Current |
|||||
|---|---|---|---|---|---|---|
|
Three Ø |
Single Ø |
|||||
|
200 V |
230 V |
460 V |
575 V |
115 V |
230 V |
|
|
1/6 |
— |
— |
— |
— |
4.4 |
2.2 |
|
1/4 |
— |
— |
— |
— |
5.8 |
2.9 |
|
1/3 |
— |
— |
— |
— |
7.2 |
3.6 |
|
1/2 |
2.5 |
2.2 |
1.1 |
0.9 |
9.8 |
4.9 |
|
3/4 |
3.7 |
3.2 |
1.6 |
1.3 |
13.8 |
6.9 |
|
1 |
4.8 |
4.2 |
2.1 |
1.7 |
16 |
8 |
|
1-1/2 |
6.9 |
6.0 |
3.0 |
2.4 |
20 |
10 |
|
2 |
7.8 |
6.8 |
3.4 |
2.7 |
24 |
12 |
|
3 |
11.0 |
9.6 |
4.8 |
3.9 |
34 |
17 |
|
5 |
17.5 |
15.2 |
7.6 |
6.1 |
56 |
28 |
|
7-1/2 |
25.3 |
22 |
11 |
9 |
80 |
40 |
|
10 |
32.2 |
28 |
14 |
11 |
— |
50 |
|
15 |
48.3 |
42 |
21 |
17 |
— |
— |
|
20 |
62.1 |
54 |
27 |
22 |
— |
— |
|
25 |
78.2 |
68 |
34 |
27 |
— |
— |
|
30 |
92 |
80 |
40 |
32 |
— |
— |
|
40 |
120 |
104 |
52 |
41 |
— |
— |
|
50 |
150 |
130 |
65 |
52 |
— |
— |
|
60 |
177 |
154 |
77 |
62 |
— |
— |
|
75 |
221 |
192 |
96 |
77 |
— |
— |
|
100 |
285 |
248 |
124 |
99 |
— |
— |
|
125 |
359 |
312 |
156 |
125 |
— |
— |
|
150 |
414 |
360 |
180 |
144 |
— |
— |
|
200 |
552 |
480 |
240 |
192 |
— |
— |