Article 110.14 (B): Splices. 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 as 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. Wiring connectors or splicing means installed on conductors for direct burial shall be listed for such use.