Tap conductor rules are located in Article 240 in the National Electrical Code (NEC). A tap conductor (as used in Article 240) has overcurrent protection ahead of its point of supply that exceeds the value permitted for similar conductors that are protected as described elsewhere in 240.4 [240.2].
Jim Dollard has an extensive background in codes and standards. If you have a query about the National Electrical Code (NEC), Jim will help you solve it. Questions can be sent to email@example.com. Answers are based on the 2014 NEC. Threadless couplings