Simply twisting is not enough. You need a mechanical connection as well. Wire nut, crimp, etc.
110.14 Electrical Connections
Because of different characteristics of dissimilar metals, devices
such as pressure terminal or pressure splicing connectors and
soldering lugs shall be identified for the material of the conductor
and shall be properly installed and used. Conductors of dissimilar
metals shall not be intermixed in a terminal or splicing connector
where physical contact occurs between dissimilar conductors (such as
copper and aluminum, copper and copper-clad aluminum, or aluminum and
copper-clad aluminum), unless the device is identified for the purpose
and conditions of use. Materials such as solder, fluxes, inhibitors,
and compounds, where employed, shall be suitable for the use and shall
be of a type that will not adversely affect the conductors,
installation, or equipment.
Conductors shall be spliced or joined with splicing devices identified
for the use or by brazing, welding, or soldering with a fusible metal
or alloy. Soldered splices shall first be spliced or joined so as to
be mechanically and electrically secure without solder and then be
soldered. All splices and joints and the free ends of conductors shall
be covered with an insulation equivalent to that of the conductors or
with an insulating device identified for the purpose.
Wire connectors or splicing means installed on conductors for direct
burial shall be listed for such use.