This comprehensive guide walks you through NEC requirements, ampacity calculations, and real-world considerations that every electrician needs to master. Calculate proper wire gauge based on NEC standards. Input your electrical parameters to get accurate wire size. This guide will show you how to count the wires in an electrical box. Tools and Materials Needed Steps to Count Wires 1. Electrical Tips and Be Sure to Subscribe! Part (1) of Section 370-16 (a) describes in detail the method of counting wires, as well as clamps, fittings, or devices (i., switches, receptacles, combination devices) - by establishing.