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Electrical Motors Efficiency Ratings

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The efficiency of an electrical motor is the ratio mechanical power output to the electric power input.

NEMA has established the efficiency index:

Electrical Motors Efficiency Ratings
NEMA Letter IndexNominal EfficiencyMinimum Efficiency
A   95.0
B 95.0 94.1
C 94.1 93.0
D 93.0 91.7
E 91.7 90.2
F 90.2 88.5
G 88.5 86.5
H 86.5 84.0
K 84.0 81.5
L 81.5 78.5
M 78.5 75.5
N 75.5 72.0
P 72.0 68.0
R 68.0 64.0
S 64.0 59.5
T 59.5 55.0
U 55.0 50.5
V 50.5 46.0
W   46.0

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