National Electrical Installation Standards

Standards as High as Your Own

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Tuesday, March 13, 2018

Question:

Hi Charlie, On a 3 phase motor that is driven by a VFD, is the disconnect required in section 430.102 B (1) allowed to be omitted as per the exception (a) due to the fact that opening the disconnect while the VFD and motor are under load will cause damage to the VFD? By installing the disconnect between the drive and the motor we are creating an opportunity to cause damage to the drive if opened under load.

Reggie Gassman

A

Answer:

Hey Reggie thanks for your question. Yes. The informational Note to 430.102(B) Exception (a) includes motors associated with adjustable drives as an example for not installing a disconnecting means within sight of that motor. The controller disconnecting means must be lockable in accordance with 110.25. Opening a disconnect switch and deenergizing a motor supplied from an adjustable drive without deenergizing the drive can damage the drive.

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