NFPA 70 General Requirements and Wiring Methods
The general rules that apply to every low-voltage job
Article 100 definitions and Article 110 general requirements apply before any Chapter 3 wiring method is selected. Equipment must be listed and installed per its instructions (110.3). Terminations must be suitable for the conductor material and temperature (110.14). Working clearance in front of electrical equipment is a classic exam topic: 110.26 requires adequate depth, width, and height, and 110.26(E) protects the dedicated equipment space above and in front of switchboards and panelboards.
Wiring methods
- Chapter 3 methods include NM cable (Article 334), PVC conduit (352), EMT (358), and MC cable (330).
- Conductors must be protected from physical damage (300.4), and burial depths must comply with 300.5 when cable is direct-buried.
- Splices and joints must be in accessible boxes or enclosures (300.15), and raceway fill is limited by Chapter 9 tables.
- Cables and raceways need support and securement at the intervals and within the distances required by their specific article.
Worked example
A 208Y/120-volt panelboard is 24 inches wide and has exposed live parts. The working space in front must be at least 36 inches deep for 120 volts to ground, at least 30 inches wide, and at least 6 feet 6 inches high. The 30-inch width is not reduced to the 24-inch panel width. The dedicated space above the panel must also be kept clear of foreign piping and ductwork.
Traps that cost marks
- Measuring working-space width as the equipment width instead of the required minimum.
- Storing boxes or raceways in the dedicated equipment space.
- Using NM cable in wet or damp locations where it is not permitted.
- Overfilling conduit or exceeding bend limits between pull points.