UL 1333 FEP Wire 20 AWG — 13-mil Thin Wall at 150°C, 300 Vac for Dense Internal Harnesses
UL 1333 in 20 AWG is a single-conductor appliance wiring material with extruded FEP insulation, rated 150°C maximum at 300 Vac with a horizontal flame rating. Its insulation is specified as a single uniform wall — 13 mils minimum average thickness, 12 mils minimum at any point — applied across the entire 30 AWG to 10 AWG conductor range with no bracket table. That wall is roughly a third thinner than the 20 mils specified at the same gauge in UL 1330 and UL 1331, and it is the defining characteristic of the style. CableApex supplies UL 1333 20 AWG as a UL Recognized Component — file on record.
What a Thinner Wall Changes in a Harness
Insulation thickness is applied on every side of the conductor, so a reduction from 20 mils to 13 mils removes roughly 14 mils from the finished outside diameter of the wire. On a fine 20 AWG conductor that is a substantial proportional change, and it compounds across a bundle: in a harness of twenty conductors, the cross-sectional area saved is enough to alter whether the bundle passes through a given grommet, whether it clears an adjacent component, or whether an existing routing channel still has capacity when a circuit is added late in a design.
Two secondary effects follow from the same reduction. Bend radius improves, because a thinner polymer wall resists deformation less and the wire conforms to a tighter turn without stressing the insulation at the outside of the bend — useful where a lead has to reverse direction in a confined space. And weight drops, both from the polymer removed and from the smaller volume of the finished bundle, which matters in portable equipment and in assemblies where harness mass is carried on brackets rather than supported along its length.
Wall and Finished Diameter at 20 AWG
| Style | FEP wall at 20 AWG | Relative finished diameter | Voltage rating |
|---|---|---|---|
| UL 1333 (this page) | 13 mils avg / 12 mils min | Slimmest of the three | 300 Vac |
| UL 1331 | 20 mils avg / 18 mils min | Larger | 600 Vac |
| UL 1330 | 20 mils avg / 18 mils min | Larger | 600 Vac |
The trade is explicit and worth stating plainly: the thinner wall comes with a 300 Vac rating rather than 600 Vac. Where the circuit is genuinely a 300 V class circuit, that is a specification matched to the requirement rather than a compromise. Where the circuit needs 600 Vac, the thicker-wall styles are the correct choice and the diameter follows from the voltage class.
UL 1333 20 AWG Specifications
| Item | Specification |
|---|---|
| UL Style | 1333 — single conductor with extruded insulation |
| Temperature Rating | 150°C maximum |
| Voltage Rating | 300 Vac; tag may also indicate 600 Volts Peak for electronic use only |
| Conductor | 20 AWG, solid or stranded, or Litz cable magnet wire (style range 30–10 AWG) |
| Insulation | Extruded FEP, 13 mils minimum average thickness, 12 mils minimum at any point |
| Optional Covering | Extruded FEP, 10 mils minimum at any point; or glass braid, 7 mils minimum at any point |
| Flame Rating | Horizontal flame; VW-1 vertical flame test available |
| Oil Rating | Optional — 80°C oil resistant |
| Gasoline Resistance | Optional |
| UL Recognition | UL Recognized Component — file on record |
| Marking | Per UL Subject 758 marking requirements; Litz product additionally marked “Litz conductors are manufactured using solderable magnet wire” |
| Permitted Use | Internal wiring of appliances |
| RoHS / REACH | Documentation available on request |
The 600 V Peak Electronic Tag
UL 1333 permits the tag to indicate 600 Volts Peak for electronic use only, in addition to the base 300 Vac rating. This covers internal electronic circuits where the peak voltage excursion exceeds the RMS working voltage — switching waveforms, transformer secondaries and similar circuits where the instantaneous peak is the governing figure rather than the continuous AC rating. It is a marking option specified at time of order, not a separate voltage class, and neither UL 1330 nor UL 1331 lists it. Where a design needs a thin-wall fluoropolymer wire in an electronic circuit with peaks above the 300 V working level, this tag is the reason UL 1333 is often the applicable style.
Applications
Within its permitted use — internal wiring of appliances — UL 1333 20 AWG suits densely bundled internal harnesses, control and signal wiring in space-constrained assemblies, and internal electronic circuit connections where the 600 V peak tag applies. The thin wall makes it the practical choice where bundle diameter or bend radius governs the routing rather than the current or the working voltage. Litz construction is available for high-frequency winding leads. Optional 80°C oil resistance and optional gasoline resistance are available where lubricant or fuel contact is expected. For applications outside internal appliance wiring, confirm application suitability before specifying.
Key Features
- 13 mils uniform wall — roughly a third thinner than the 600 V FEP styles
- Smaller finished diameter, tighter bend radius and lower harness mass
- 600 V peak electronic use tag available in addition to the 300 Vac rating
- Solid, stranded or Litz cable magnet wire conductor construction
- Optional FEP or glass braid covering; optional 80°C oil and gasoline resistance
- UL Recognized Component — file on record
Request a Quote
CableApex supplies UL 1333 20 AWG from 100 m per color and responds to B2B inquiries within 12 hours. Specify conductor construction (solid, stranded or Litz), colors, covering option, the 600 V peak tag if required, and any oil or gasoline requirements through the form below.
Related FEP styles: UL 1331 FEP Wire (150°C / 600 Vac) · UL 1330 FEP Wire (200°C / 600 Vac) · UL 1333 FEP Wire category
