110.14 (A)
"Terminals. Connection of conductors to terminal parts
shall ensure a thoroughly good connection without damaging
the conductors and shall be made by means of pressure connectors
(including set-screw type), solder lugs, or splices to
flexible leads. Connection by means of wire-binding screws or
studs and nuts that have upturned lugs or the equivalent shall
be permitted for 10 AWG or smaller conductors."
