UL498 (Attachment Plugs and Receptacles) seems to refer to both stranded and solid wire for most sections, with the execption of push terminals for field wiring, which are solid only. There is a lot of "shall be wired with solid or stranded" language for the various tests. IMO, this suggests the devices should work with both, but could perhaps be lab tested in only one configuration or the other. See attached UL498 standard for reference
