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Circuit Overload Protection for Hermetic Motors, Part 2

circuit-overload-protection-for-hermetic-motors-part-2You must use one of four methods to protect the motor-compressor control apparatus, disconnecting means, and branch-circuit conductors against overload and failure to start [440.52(B)]. These are:

  1. An overload relay selected per 440.52(A)(1); that is, it must be responsive to motor current. It must trip at not more than 140% of the motor-compressor rated-load current.
  2. A thermal protector integral with the motor-compressor; it must not permit a continuous current in excess of 156% of the marked rated-load current or branch-circuit selection current.
  3. A fuse or inverse time breaker that’s responsive to motor current.
  4. A system that protects on the basis that it will prevent dangerous overheating of the motor-compressor due to overload and failure to start. It must be approved (by the authority having jurisdiction) for the use. It also must not permit a continuous current in excess of 156% of the marked rated-load current or branch-circuit selection current.

If you the overload relays and/or other devices you use for motor overload aren’t capable of opening a short circuit, you must provide protection for those devices [440.53]. The protection must be fuses or inverse time breakers with ratings or settings that comply with Article 440, Part III. The exception to this last requirement is if those overload protection devices are identified for group installation or for part-winding motors and are marked to indicate the maximum size of fuse or breaker protecting them.

« Part 1 | Source: Mark Lamendola | Mindconnection