Vast majority of automation & controls that I came across was solid wire especially #16 guage & smaller. Any time we ran these in conduit we used solid wire if #16 or 14 guage. If we ran Beldon type of low voltage cable it had stranded conductors. At the 5 million square foot campus that I retired from we had over 500 VFD'S. All had THWW for line & loads on VFD'S. Some were on plain Jane NEMA frame motors from the 1960's. All had a copper properly sized ground conductor from drive to motors. Tried to keep wire length from drives to motors under 100'. Had four VFD'S for 75 HP cooling towers that were several hundred feet away but never gave us any problems. A few months ago a poster stated he now only uses believe he said Type XHHN wire for drives. To me that would be a better choice.
