National Electrical Installation Standards

Standards as High as Your Own

Wednesday, December 27, 2017


Re: CQD answer published Thursday, December 21 - Adjustable Speed Drive

I would just like to comment on the dialog below. VFD's are most always Listed devices, many to UL508, Industrial Control Products. As such, they are required to be installed per the manufacturer's instructions. This includes, but is not limited to, proper supplementary enclosure, spacings for necessary cooling, overcurrent protection, and conductor ampacity.

Best Wishes for a Safe and Happy Holiday season, Nick Abbatiello



Hey Nick thanks for your comment. You make a good point manufacturer's instructions included with listed or labeled equipment must be followed as stated in 110.3(B). Those instructions can have limitations that are more restrictive than those in NEC rules.

Here is some additional information from UL Product Spec:

Power Conversion Equipment, NMMS

The basic standard used to investigate products in this category is ANSI/UL 508C, "Power Conversion Equipment," or ANSI/UL 61800-5-1, "Adjustable Speed Electrical Power Drive Systems - Part 5-1: Safety Requirements - Electrical, Thermal and Energy."

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