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November 2017
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Understanding the big picture of efficiency

In accordance to recent changes in motor efficiency laws, it is now mandatory that continuous duty motors for integral gearmotors be Premium Efficient. It is important to recognize that this requirement only applies to continuous duty motors. Motors rated for intermittent operation (for non-continuous applications) are not required to be Premium Efficient. Premium Efficient motors have more rotating mass (or inertia) and this increased inertia takes energy to start and stop. In fact, in many dynamic or high cycling applications, a Premium Efficient motor can actually consume more electrical energy than a low inertia, lower efficiency design. 

The rated motor efficiency in itself doesn’t tell the whole story about energy consumption. The correct perspective for energy savings is to focus on the consumed energy for a whole system and not the motor rated efficiency alone. A higher rated motor efficiency does not ensure lower energy usage in an actual application. 

Continuous Duty vs. Intermittent Duty

The basic decision for determining Continuous vs. Intermittent duty is rather easy. If the motor is switched on and runs continuously then the motor should be rated for continuous duty. If the motor is switched on for a short time or has a cyclic operation, then the motor can be rated intermittent operation and the motor has no efficiency requirement. As a rule of thumb, if the motor is running more than one hour continuously with no switching on or off during that time, then, in general, the application is continuous and a Premium Efficient continuous duty motor is required. If the motor runs for less than an hour continuously, then the application can be considered intermittent.

Examples of Intermittent Applications

  • Crane drives (travel & hoist)
  • Doors
  • Hoists & lifts
  • Metering pumps
  • Packaging equipment
  • Palletizing
  • Punch presses
  • Slide gates
  • Turntables
  • Winders & coilers

Examples of Continuous Applications

  • Bucket elevators
  • Bulk material handling conveyors
  • Continuous flow pumps
  • Continuous mixers

Submitted by Nord Drive Systems
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