How to Choose Between THHN and Romex: UL Certification, Ampacity, and Project Cost
THHN and Romex are both 600V rated but differ in construction, installation, and application. THHN is a single-conductor wire for conduit in commercial and industrial settings; Romex (NM-B) is a multi-conductor sheathed cable for dry indoor residential and light commercial wiring. Selection depends on UL certification, ampacity, environment, code, and total cost—not unit price alone. […]