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Why Explosion-Proof Motors Need Special Considerations

Mike Jeffries | March 2, 2017

ExplosionProofMotors.jpegSometimes, explosion-proof motors need to be installed in an environment that carries combustible vapors and dust which can get ignited by heated motors. These type of motors are selected based on special considerations:

Related Blog: Can You Use a Variable Frequency Drive (VFD) on a Single Phase Motor?

1. Motor Classification
Motors are broken down into separate categories based on class, division, and group. Class I motors can be placed in an environment where explosive vapors are present. Class II motors are used in places where large amounts of electrically conductive dust is present. Class III motors keep dust out and ensure the motor's temperature does not rise enough to cause an explosion.

2. Code Letters
It is important to remember the different code letters that assign each class of motor for different combustible substances. A chart is provided specifying which class of motor needs to be used in a specific environment, from Group A to Group G, and this chart needs to be adhered to. A further distinction between environments is made with Division 1, where the combustible material will be present near the motor at all times, and Division 2, where ignitable materials may be present near the motor under abnormal conditions.

3. Explosion-Proof Listing
The UL listing of a motor as explosion-proof is crucial to certify that it has been built according to the UL's requirements. A motor that has been restored or rebuilt needs to be re-certified by the UL, which will visit the service center where the motor is being repaired to ensure it meets their requirements. After being rebuilt, the motor needs to belong to the same class and group it belonged to before rebuilding.

4. Service Center Responsibility
If mechanical or electrical remodeling of a motor has been outsourced, it is still the responsibility of the UL-approved service center to ensure that the motor's ability to contain an explosion remains unchanged. The service center must also provide winding-over service protection to the rebuilt motor. The motor leads can also be potted, a preferred option for most motors and a requirement for explosion-proof motors.

5. Variable Frequency Drives
While using VFDs, the manufacturer must provide details about the speed range in which the motor meets the temperature requirements of the listing. Unlisted motors cannot be used with VFDs for inverter duty.

These factors must be taken into account while selecting explosion-proof motors to ensure they are compatible with their immediate surroundings and no dangerous accidents occur during their operation.

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Topics: motor safety, explosion-proof motors, UL listing

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