UL1331 FEP Wire

UL 1331 FEP Wire — 150°C, 600 Vac Appliance Wiring with Litz Conductor and Dual Oil Rating Options

UL 1331 is a single-conductor appliance wiring material with extruded FEP insulation, rated 150°C maximum at 600 Vac with a horizontal flame rating, evaluated under UL Subject 758. It spans conductor sizes from 30 AWG through 4/0 AWG in solid or stranded construction, and additionally permits Litz cable conductors built from Recognized Component magnet wire. Among the FEP appliance wiring styles CableApex supplies, UL 1331 is the one that combines the full 600 Vac insulation class with the Litz conductor option and a choice of two oil-resistance temperatures. CableApex supplies UL 1331 as a UL Recognized Component — file on record.

600 Vac at 150°C: Where UL 1331 Fits

The FEP appliance wiring styles differ primarily in how temperature rating, voltage rating and insulation wall combine. UL 1331 pairs a 600 Vac insulation class with a 150°C maximum temperature rating — a combination that suits appliance internal wiring operating at line voltage in genuinely hot zones, but where the 200°C ceiling of UL 1330 is more than the design requires. Because both styles share the same 30 AWG–4/0 AWG conductor range and nearly identical wall brackets, substituting between them is straightforward at the specification stage, and the choice generally comes down to whether the application genuinely reaches beyond 150°C.

Insulation Wall Brackets

The extruded FEP wall scales across three conductor-size brackets. Sizes 30 AWG through 10 AWG carry 20 mils minimum average thickness with 18 mils minimum at any point, the bracket that covers all common hook-up and lead wire gauges. From 8 AWG through 2 AWG the wall increases to 30 mils average with 27 mils minimum. The heaviest bracket, 1 AWG through 4/0 AWG, specifies 45 mils average and 40 mils minimum at any point. Note that the bracket boundaries in UL 1331 are not identical to those in UL 1330 — the middle bracket here begins at 8 AWG rather than 9 AWG — so wall thickness should be confirmed against the correct style when a design sits close to a bracket edge.

Litz Cable Conductor Construction

UL 1331 permits Litz cable conductors constructed from Recognized Component magnet wire (OBMW2) rated at a minimum of 150°C. Under this style, the individual magnet wire strands are cabled together to form a single conductor, and the resulting AWG size is established by the DC Resistance Test rather than by physical measurement, since each strand carries its own enamel insulation. Litz construction is specified where the circuit carries high-frequency current: subdividing the conductor into many individually insulated strands reduces the skin-effect and proximity-effect losses that would otherwise concentrate current at the surface of a solid or conventionally stranded conductor. Typical uses include transformer and inductor windings, induction heating coils and switching power supply magnetics.

Product supplied with Litz conductors carries a mandatory additional marking. The tag or reel must be plainly marked: “Litz conductors are manufactured using solderable magnet wire.” This marking applies to all Litz-conductor product under this style and is not optional.

Covering and Optional Ratings

An optional covering may be applied over the FEP insulation: either extruded FEP at 2 mils minimum thickness, or a glass braid at 7 mils minimum thickness. The 2 mils FEP covering option is notably thinner than the 10 mils minimum specified in the neighbouring FEP styles, allowing a secondary fluoropolymer layer to be added with minimal increase in finished diameter — useful where a colour-coded or additional-protection outer layer is wanted without compromising harness fill. Optional oil resistance is available at either 60°C or 80°C, and optional gasoline resistance may also be specified. All optional ratings and coverings are specified at time of order rather than being standard on all product.

Comparing the Three FEP Styles

Across the FEP appliance wiring group, UL 1330 is the 200°C / 600 Vac style with three wall brackets and gasoline-immersion tag options; UL 1331 is the 150°C / 600 Vac style with the same broad conductor range, Litz construction, dual oil-temperature options and the thinnest optional FEP covering; and UL 1333 is the 150°C / 300 Vac thin-wall style over a narrower 30–10 AWG range, also permitting Litz conductors and adding a 600 V peak electronic tag option. Where the requirement is 600 Vac at 150°C with Litz construction available, UL 1331 is the style that carries that combination.

Permitted Use and Ordering

The permitted use for UL 1331 is internal wiring of appliances. For applications outside internal appliance wiring, confirm application suitability before specifying. Marking follows UL Subject 758 marking requirements, with the additional mandatory Litz marking where Litz conductors are supplied. RoHS/REACH documentation is available on request. CableApex supplies UL 1331 from 100 m per color, in solid, stranded or Litz conductor construction, with or without the optional FEP or glass braid covering, and answers B2B inquiries within 12 hours with pricing, lead time and packing details. Browse the UL 1331 products below by AWG size, or submit your specification through any product page inquiry form.