Motors, Part 7

Where you locate a motor does matter. The NEC has two basic requirements [430.14]:

  1. Allow for adequate ventilation around the motor (doesn’t apply to submersibles).
  2. Provide room for maintenance (e.g., lubricating bearings).

What does “adequate ventilation” mean? One reason the NEC doesn’t specify is because what qualifies as adequate in one location may not be adequate in another location.

Consider this example. Motor A runs a conveyor in an ambient temperature ranging from 68 degrees F to 78 degrees F. But Motor B runs a hot process extruder in a room where the ambient temperature is usually above 90 degrees F.

There’s not much air movement around Motor A, because it’s stuffed under the conveyor. But a forced air cooling duct provides significant air circulation around motor B.

As you can see, several factors affect how much free space you need around a motor to ensure it’s adequately ventilated. How can you ensure that you meet the motor ventilation requirements?

When designing a new installation, you can calculate how much air flow is needed to exchange winding heat with the ambient air and choose a location that meets the minimum. If there isn’t such a location, you may improve the heat exchange ability with passive ducting or forced air ducting. Installing thermal shielding between the motor and the heat source (e.g., a hot process) also improves the heat exchange.

For an existing installation, verify airflow adequacy with a thermal camera. If you can’t relocate the motor, provide air ducting and/or thermal shielding.

« Part 6 | Part 8 » | Source: Mark Lamendola | Mindconnection

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