THHN is een kabelaanduiding volgens NEC / UL (USA): T = Thermoplastic (PVC) insulation; HH = High heat resistant, 90 C (one H means 75 C); N = Nylon outer covering; THHN = Thermoplastic high heat-resistant nylon-coated building wire. 600 V, 90 C dry and damp locations. UL 83; NEC Article 310.