motor confusion

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MR. S

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OK, If the motor is a NEMA design B,C,D or E, art. 110.14(c)(1)(b) says I can take my wire size out of the 75 degree column, if my wire is rated for 75 degrees. If my motor is a NEMA design B, C, or D, my LRA comes from T.430.251(B). I'm good with that.
If my motor has a code letter A thru V, I follow 430.7(B) for my LRA, and I use the 100 amp rule for selecting my conductor size. I'm good with that also. My question is why do some motor name plates have a design letter and a code letter? Which one do I follow? Thanks, MR. S
 
MR. S said:
OK, If the motor is a NEMA design B,C,D or E, art. 110.14(c)(1)(b) says I can take my wire size out of the 75 degree column, if my wire is rated for 75 degrees. If my motor is a NEMA design B, C, or D, my LRA comes from T.430.251(B). I'm good with that.
If my motor has a code letter A thru V, I follow 430.7(B) for my LRA, and I use the 100 amp rule for selecting my conductor size. I'm good with that also. My question is why do some motor name plates have a design letter and a code letter? Which one do I follow? Thanks, MR. S
Click to expand...
Look at 430.7(A)(9).
 
430.7(A)(9) only tells me that the design letter shall be marked on the name plate. Unfortunately I do not have the resources for the informational note. The only thing I know about the design letter is that NEMA started using them after 1996.
 
So if there is both on the name plate, the NEMA letter is for the torque rating? that would make sense. If that were the case, then I would use the code letter, not the NEMA letter, and T.430.7(B)
 
MR. S said:
So if there is both on the name plate, the NEMA letter is for the torque rating? that would make sense. If that were the case, then I would use the code letter, not the NEMA letter, and T.430.7(B)
Click to expand...

I hope this sheds some light on this issue for you.

General you can anticipate motors to be design B torque curve but these are the others for comparison:
NEMA design A
?maximum 5% slip
?high to medium starting current
?normal locked rotor torque
?normal breakdown torqueNEMA
?suited for a broad variety of applications - as fans and pumps
NEMA design B
?maximum 5% slip
?low starting current
?high locked rotor torque
?normal breakdown torque
?suited for a broad variety of applications, normal starting torque - common in HVAC application with fans, blowers and pumps
NEMA design C
?maximum 5% slip
?low starting current
?high locked rotor torque
?normal breakdown torque
?suited for equipment with high inertia starts - as positive displacement pumps
NEMA design D
?maximum 5-13% slip
?low starting current
?very high locked rotor torque
?suited for equipment with very high inertia starts - as cranes, hoists etc.

The following was as included in the "Engineering ToolBox" for kva/hp "code" letters.

NEMA - The National Electrical Manufacturer's Association - who sets the design standards for motors, has established a NEMA Code letter designation to classify motors by the ratio of locked rotor KVA per horsepower.

Then the code letters are:
NEMA
Code Letter KVA/HP
with locked rotor Approximate Mid-Range Value
A 0-3.14 1.6
B 3.15-3.55 3.3
C 3.55-3.99 3.8
D 4.0-4.49 4.3
E 4.5-4.99 4.7
F 5.0-5.59 5.3
G 5.6-6.29 5.9
H 6.3-7.09 6.7
J 7.1-7.99 7.5
K 8.0-8.99 8.5
L 9.0-9.99 9.5
M 10.0-11.19 10.6
N 11.2-12.49 11.8
P 12.5-13.99 13.2
R 14.0-15.99 15.0
S 16.0-17.99
T 18.0-19.99
U 20.0-22.39
V 22.4-and up

In general it is accepted that small motors requires higher starting KVA than larger motors. Standard 3 phase motors often have these locked rotor codes:

?less than 1 hp: Locked Rotor Code L, 9.0-9.99 KVA
?1 1/2 to 2 hp: Locked Rotor Code L or M, 9.0-11.19
?3 hp : Locked Rotor Code K, 8.0-8.99
?5 hp : Locked Rotor Code J, 7.1-7.99
?7.5 to 10 hp : Locked Rotor Code H, 6.3-7.09
?more than 15 hp : Locked Rotor Code G, 5.6-6.29
 
templdl said:
I hope this sheds some light on this issue for you.

General you can anticipate motors to be design B torque curve but these are the others for comparison:
NEMA design A
?maximum 5% slip
?high to medium starting current
?normal locked rotor torque
?normal breakdown torqueNEMA
?suited for a broad variety of applications - as fans and pumps
NEMA design B
?maximum 5% slip
?low starting current
?high locked rotor torque
?normal breakdown torque
?suited for a broad variety of applications, normal starting torque - common in HVAC application with fans, blowers and pumps
NEMA design C
?maximum 5% slip
?low starting current
?high locked rotor torque
?normal breakdown torque
?suited for equipment with high inertia starts - as positive displacement pumps
NEMA design D
?maximum 5-13% slip
?low starting current
?very high locked rotor torque
?suited for equipment with very high inertia starts - as cranes, hoists etc.

The following was as included in the "Engineering ToolBox" for kva/hp "code" letters.

NEMA - The National Electrical Manufacturer's Association - who sets the design standards for motors, has established a NEMA Code letter designation to classify motors by the ratio of locked rotor KVA per horsepower.

Then the code letters are:
NEMA
Code Letter KVA/HP
with locked rotor Approximate Mid-Range Value
A 0-3.14 1.6
B 3.15-3.55 3.3
C 3.55-3.99 3.8
D 4.0-4.49 4.3
E 4.5-4.99 4.7
F 5.0-5.59 5.3
G 5.6-6.29 5.9
H 6.3-7.09 6.7
J 7.1-7.99 7.5
K 8.0-8.99 8.5
L 9.0-9.99 9.5
M 10.0-11.19 10.6
N 11.2-12.49 11.8
P 12.5-13.99 13.2
R 14.0-15.99 15.0
S 16.0-17.99
T 18.0-19.99
U 20.0-22.39
V 22.4-and up

In general it is accepted that small motors requires higher starting KVA than larger motors. Standard 3 phase motors often have these locked rotor codes:

?less than 1 hp: Locked Rotor Code L, 9.0-9.99 KVA
?1 1/2 to 2 hp: Locked Rotor Code L or M, 9.0-11.19
?3 hp : Locked Rotor Code K, 8.0-8.99
?5 hp : Locked Rotor Code J, 7.1-7.99
?7.5 to 10 hp : Locked Rotor Code H, 6.3-7.09
?more than 15 hp : Locked Rotor Code G, 5.6-6.29
Click to expand...
Thanks ,that does help.
 
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