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Controllers for Hermetic Motors

controllers-for-hermetic-motorsPart V of Article 440 provides the requirements for hermetic motor controllers, and is the shortest of the six parts. It consists of only one Subsection, namely 440.1. And that’s divided into (A) and (B); those have two sentences and one sentence, respectively.

Part V is short, but no cakewalk. That fact hits you when you read the first sentence of 440.41(A). Let’s break that sentence down so it’s not such a mind-bender.

The controller needs two ratings:

  1. A continuous-duty full-load current rating.
  2. A locked-rotor current rating.

The locked-rotor current rating can’t be less than the nameplate rated-load current or branch-circuit selection current. If it’s less than either one, you’ve got a Code violation. It can’t be less than the locked-rotor current of the motor, either.

But what if the motor is rated in horsepower and doesn’t have the nameplate rated-load current rating and/or the locked-rotor current rating? This takes us into the second sentence. What you have to do in that case is determine the equivalent:

  • Full-load current rating from Tables 430.248, 249, and 250.
  • Locked-rotor current rating from Tables 430.251(A) and (B).

If the controller serves more than one load, then its:

  • Continuous-duty full-load current rating.
  • Locked-rotor current rating.

...must each be at least as large as the combined load as determined per 440.12(B) (that is also a mind-bender, so read carefully!)

Source: Mark Lamendola | Mindconnection