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REA Bulletin 160-3

Engineering and Operations Manual: Service to Induction Motors

REA Bulletin 160-3 Engineering and Operations Manual: Service to Induction Motors

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Date Published:

Oct 1969


Section III of the REA Engineering and Operations Manual covers electric service to induction motors, including voltage dip and flicker limits.


Service to motors larger than three horsepower requires careful study to assure that a satisfactory installation will result.

Motors are relatively sensitive to voltage and may overheat if the supply voltage is too high or too low, or, in the case of three-phase motors, if the phase voltages are unbalanced. It is important, therefore, that the supply voltage be kept within a range thet will permit the motor running voltage to be as close to nameplate rating as feasible.

Deficiencies in the consumer's installation also may cause the motor to overheat. The installation, therefore, should be checked for adequate wiring, ventilation and motor protection.

Proposed motor installations must be appraised for any possible adverse effect on other consumers. The starting of a motor causes a voltage dip which may cause light flicker, TV picture distortion or, in an extreme case, may cause other motors to drop off the line.

It is also possible that the voltage dip on starting may be so great that the motor will not start, or if it does start, that it will not come up to speed.

These considerations make it very important that the probable voltages during running and starting conditions be determined prior to the installation of service facilities. This publication discusses service to motors primarily from this point of view. It also includes material on motor control and provides methods for calculating voltage and voltage dip during starting and running conditions.