When the length of half coupling employed on the motor is much smaller than length of motor shaft extension key should be reduced by length 'A' calculated from the following formula

A = (L1 - L2) (L1 - L2)/2-5.0 mm 
      ----------- 
            2

Where,

L1 = Length of shaft extension key supplied with the motor, mm
L2 = Length of coupling engaging with shaft extension key, mm.

Vibration of the motor with this reduced length key and half-coupling should not exceed more than 5 to 7 microns over the vibration figures obtained during testing at KEC works.

Key to be located in the shaft key way by a 3 mm spot weld to prevent its migration.