What type of wiring does Article 398 cover?

Article 398 of the National Electrical Code (NEC) specifically addresses Open Wiring on Insulators. This type of wiring involves electrical conductors that are supported by insulators mounted on structures, which keeps the wiring above the ground. This method is particularly designed for outdoor applications or where physical protection from environmental factors is necessary, as insulators help prevent short circuits and ensure safe operation without direct contact with conductive surfaces.

Open wiring on insulators has historical significance and is mainly used where traditional conduit may not be practical. It's essential for ensuring adequate clearance to minimize potential hazards associated with contact or environmental damage.

The other types of wiring mentioned in the choices apply to different contexts. Messenger-supported wiring refers to a system where conductors are suspended from a cable (messenger), while surface nonmetallic raceways involve enclosed pathways for electrical wires. Concealed knob-and-tube wiring is an older wiring method that used ceramic knobs and tubes for support and protection, widely replaced by safer and more efficient systems. Each of these categories has its own NEC articles, highlighting the need for proper application and understanding of electrical installations.