I am installing (3) VFDs and it will require #8 AWG wire on the output side of each drive. What is the recommended type of wire for the output side of VFDs? I have heard that it is not a good idea to install THHN on the output side. Is this accurate? The application is (3) 25HP Blower Motors.
If you are going to use single conductors THHN is probably as good as anything.
Some people have been advocating the use of special VFD cables that the cable manufacturers are now pushing. I think they are one of those things that make sense in some cases, but I also think that most times you won't see any real difference in performance between running single conductors and the expensive cables, especially if the single conductors are run in EMT or ferrous metal conduit.
If it makes you feel better, twist the single conductors together with a drill before pulling them. IMO, you will get most of the benefits of the expensive cables without the expense.
OTOH, most of the VFD cables are also rated as tray cable so they can be just put on a cable tray, which might be convenient.