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Motors Over 1000V

Motors Over 1000VWhen you’re using higher voltages, there are additional hazards. Thus, Part XI of Article 430 adds to or amends other provisions of the same Article. You must also apply the other provisions, but add or modify per the Part XI requirements.

One of those requirements is the controller must, in addition to the markings required by 430.8, also be marked with the control voltage [430.22].

The bulk of Part XI focuses on overcurrent protection [430.225]. Outside of this Section, you’ll find a few other requirements (e.g., disconnect must be lockable) but it’s here where the main concern is.

The first requirement we come across is that each motor circuit include coordinated protection [430.225(A)]. This protection must automatically interrupt both overload and fault currents. And it must do so in the:

  1. Motor.
  2. Motor-circuit conductors.
  3. Motor control apparatus.

There is an exception if operation is required to prevent a greater hazard to persons.

Overload protection is understandably more stringent for higher-voltage motors. A thermal protector must be integral to the motor or external current-sensing devices or both [430.225(B)]. Further, overload protection devices must not automatically reset after trip unless two conditions are met:

  1. The motor won’t automatically restart.
  2. Restarting won’t present a hazard to people..

Fault-current protection also has more stringent requirements . Whether a fuse or breaker, the device(s) must protect all ungrounded conductors and be arranged for safe servicing [430.225(C)]. Breakers cannot automatically reclose the circuit.

Source: Mark Lamendola | Mindconnection