UL 66

This standard states basic construction, test, and marking requirements for fixture wires. Fixture wires are single conductor and are of the following types:

• 600 volt Types: PTF, PTFF, PAF, PAFF, KF-2, KFF-2, PF, PFF, PGF, PGFF, SF-2, SFF-2, ZF, ZFF, ZHF, TF, TFF, TFN, TFFN, RFH-2, FFH-2, FFHH-2, HF, HFF, RFHH-2, and RFHH-3
• 300 volt Types: KF-1, KFF-1, SF-1, SFF-1, RFH-1, XF, and XFF

These types are for use as specified in Article 402 and other applicable parts of the National Electrical Code (NEC), ANSI/NFPA 70.