Search for "Meter Mounting Equipment" see PJSR.GuideInfo
http://database.ul.com/cgi-bin/XYV/template/LISEXT/1FRAME/ccnsrch.html I found the answer to my question, just as I suspected!
Wire connectors in Listed meter mounting equipment are intended to accommodate one conductor only unless use with more than one conductor is clearly indicated on the wiring diagram or other readily visible location.