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Motor Disconnects, Part 6

Motor Disconnects, Part 6You can use a switch or circuit breaker as both a controller and a disconnecting means for motor applications [430.111]. But only if it meets certain requirements or is one of the following:

  • Air-break switch.
  • Inverse time circuit breaker.
  • Oil switch.

If it’s not one of these, it must:

  • Have a rating that conforms to 430.83 (this provides various controller rating requirements).
  • Open all ungrounded conductors to the motor.
  • Be protected by an ovecurrent protection device in each ungrounded conductor (the OCPDs can be the branch circuit fuses).

Generally, every motor must have its own disconnect [430.112] but there are three exceptions:

  1. Multiple motors drive several parts of a single machine or apparatus (for example, a crane).
  2. One set of branch-circuit OCPDs protects a group of motors.
  3. A group of motors is in a single room within sight of the disconnect.

If there’s more than one power source to a motor (or motor-operated equipment), each source must have its own disconnect immediately adjacent to the equipment served [430.113]. This rule has two exceptions:

  1. The controller disconnect is lockable per 110.25.
  2. It’s a Class 2 remote-control circuit conforming to Article 725, rated not more than 30V, isolated and ungrounded.

In this six-part series, we’ve covered the motor disconnecting means requirements of Article 430, Part IX. Examination of Part IX reveals some basic principles. For example, the disconnect must be of the correct type and rating for the application.

« Part 5 | Source: Mark Lamendola | Mindconnection