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What Is Motor Load?

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  • Written By: Kirsten C. Tynan
  • Edited By: Lauren Fritsky
  • Last Modified Date: 26 August 2014
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A motor is a device that converts electrical energy into mechanical energy to act upon a mechanical load. The burden placed on the motor due to this mechanical activity is referred to as the motor load. Properly matching the motor load to the motor is important to prevent damage to the motor or inefficient and needlessly costly operation.

Motors perform such tasks as moving an item from one place to another, cutting it, changing its shape, and so on. The devices may be rated in terms of several factors including power output, voltage, current, and temperature at which they may be used. The power rating is sometimes casually referred to as the motor’s size. This rating represents the allowable motor load under ideal environmental conditions. Typically, a motor is chosen so the actual motor load will be somewhat less than the load capacity to allow for non-ideal conditions.

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Use of a motor that is significantly oversized in comparison to the motor load constitutes needless expense both in terms of the initial cost and the continued operation of the motor. On the other hand, a significantly oversized motor may be required when peak loads that are substantially larger than typical loads are expected. Damage to a motor may occur when it is operated under excessive motor load compared to its rated capacity. When a motor works harder than it was designed to, waste heat may be generated faster than it is dissipated given the environmental conditions under which it is operating. This results in decreased motor efficiency, reduced service life, and possibly even the motor burning out.

Motors may be designed for continuous operation with nearly constant loads such as operation of blower or conveyor belt. Such motors are more efficient than ones designed to handle sudden application of heavy loads. Motors designed for peak motor loads are less efficient but may be required in settings which involve, for example, heavy loads being lifted by hoists or other non-continuous loads. Such peak loads must be accounted for when selecting an appropriate motor.

Occasional overloading may be accounted for by a variable called the service factor of a motor. This service factor represents the amount by which the motor can be overloaded under otherwise ideal environmental conditions without sustaining significant damage. Such overloading can be done only occasionally and for a short time in each instance without significantly shortening the motor life. It should not be allowed to occur in non-ideal environmental circumstances such as at high temperatures or with dirty motor surfaces.

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