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Branch-Circuit Conductors for Hermetic Motors

Branch-Circuit Conductors for Hermetic MotorsPart IV of Article 440 provides the requirements for branch-circuit conductors used with hermetic motors.

These requirements are intended to be used as a companion to the requirements in Article 310. That means your design basis is Article 310, but you will refer to Article 440 for amendments and additions to the Article 310 requirements.

As with other motor circuits (covered in Article 430), the load calculation depends upon whether the branch-circuit supplies:

  • Just one motor [440.32]. Ampacity must be 125% of either the motor-compressor rated-load current or the branch-circuit selection current (whichever is greater).
  • Other types of loads plus a motor [430.34]. Same as above, plus (to get total ampacity) add the other loads as calculated from Article 220 and other applicable articles.
  • Other types of loads plus multiple motors [430.35]. The ampacity cannot be less than the minimum circuit ampacity marked on the equipment per 440.4(B).

And there’s this provision that applies to the last two above [440.33]. For all the motors, add up the motor-compressor rated-load currents, then the branch-circuit selection currents. Add whichever is greater to the sum of the full load currents of the motors, plus 25% of the highest motor or motor-compressor rating in the group. Two Exceptions apply [440.33].

Source: Mark Lamendola | Mindconnection