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Fixture, Machine Tool and Appliance Wiring Material (TFFN, MTW, AWM)

Fixture wire, machine tool wire and appliance wiring material are small, often stranded wires used inside equipment rather than as building wire. This sheet explains TFFN, MTW and AWM, where each belongs and how to read the markings.

Ref EL-0012NEC 402UL 1063UL 758NFPA 79

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

Fixture wire is covered by NEC Article 402 and listed to UL 66. Types such as TFFN and TFN are used for wiring inside luminaires and for some remote control and signaling circuits where the NEC permits. MTW (machine tool wire) is listed to UL 1063 and used in industrial machinery wired to NFPA 79. It is finely stranded, flexible and often dual rated with building wire types such as THHN or THWN. AWM (appliance wiring material) is UL 758 recognized wire used inside equipment and assemblies. Each AWM construction has a UL style number. AWM is a component wire for factory products, not a field wiring method.

How to identify

Read the print. Fixture wire shows the type letters and AWG, usually 18 or 16. MTW shows "MTW" and often other ratings on the same wire. AWM shows "AWM" and a style number such as 1007 or 1015, plus voltage and temperature. Look up the style number in UL's AWM style listings for its full ratings. Stranding class matters on machine and panel work. Finer stranding bends more easily.

Type comparison

Type	Listing	Where used	Field wiring use
TFFN, TFN	UL 66, NEC 402	Inside luminaires; limited control circuits	Only where Article 402 permits
MTW	UL 1063	Industrial machinery, control panels	Within machines per NFPA 79; building wire uses only if dual rated
AWM	UL 758 (recognized component)	Inside appliances and equipment	Not a building wiring method
SIS	UL 44	Switchboard wiring	Switchboard and panel use
THHN/THWN-2/MTW dual rated	UL 83 and UL 1063	Panels and conduit	As building wire under its THHN/THWN-2 rating

Key points

Fixture wire ampacity comes from NEC Table 402.5. Voltage and temperature come from Table 402.3.
NFPA 79 sets conductor colors, sizes and stranding for industrial machinery. Read the machine's spec.
AWM style numbers carry their own voltage and temperature ratings. Look them up rather than assuming.
Panel builders often require UL 508A compliant wire. Ask what listing their shop needs.
Small-gauge stranded wire needs ferrules or terminals rated for fine stranding.

Common mistakes

Selling AWM for field wiring in conduit.
Assuming all 18 AWG wire is fixture wire.
Pulling MTW-only wire as building wire.
Ignoring stranding class on control panel work.

Governing standards: NEC Article 402 (fixture wires); UL 66 (fixture wire); UL 1063 (machine tool wires and cables); UL 758 (appliance wiring material); NFPA 79 (electrical standard for industrial machinery).

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

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