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Variable frequency drive Disconnecting Means

Safety in operation & maintenance dictates that all motor-operated equipment has a means of fully disconnecting the power supply. This is a requirement of National Electrical Code (NEC) & Occupational Safety & Health Administration (OSHA) regulations. As with starters, to reduce cost & size, most variable frequency drive manufacturers don't provide a disconnect switch as part of their standard variable frequency drive package. If the optional input disconnect is not specified, a separate switch or circuit breaker must be installed. Article 430.102 of the NEC includes requirements for disconnecting means for the motor itself & for the motor drives; both sets of requirements must be satisfied. The general rules that apply are as follows:
  • Under 600 V, the variable frequency drive disconnecting means must be within sight (and less than 50 ft according to definitions) of the motor drives as specified in Article 430.102(A).
  • The variable frequency drive is not required to be in sight from the motor.
  • The variable frequency drive disconnecting means shall also be permitted as the motor disconnecting means according to Article 430.102(B).
  • The motor disconnecting means shall be in sight of the motor. See exceptions under Article 430.102(B) that would allow motor disconnecting means to be out of sight of the motor. These exceptions, if applicable, would allow one lockable disconnect to serve as both variable frequency drive & motor disconnect while not in sight of the motor.

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