UL 1333 FEP High Temp Wire 24 AWG — Fine Conductor with a Proportionally Generous 13-mil Wall
UL 1333 in 24 AWG is a single-conductor appliance wiring material with extruded FEP insulation, rated 150°C maximum at 300 Vac with a horizontal flame rating. The style applies a single wall figure across its whole 30 AWG to 10 AWG range — 13 mils minimum average, 12 mils minimum at any point — and at 24 AWG that wall is proportionally generous relative to the conductor beneath it. The result is a fine-gauge wire with more mechanical margin than its slim outside diameter would suggest. CableApex supplies UL 1333 24 AWG as a UL Recognized Component — file on record.
Why the Wall-to-Conductor Ratio Matters at Fine Gauges
Fine conductors are the ones most easily damaged in an assembly. A 24 AWG lead has little copper to resist a clamp tightened past its stop, a pinch against a sheet-metal edge, or the point load where a cable tie crosses a bracket corner. Whether the wire survives that treatment depends less on the conductor than on how much insulation sits between it and the object pressing on it.
Because UL 1333 does not scale its wall down for finer conductors, a 24 AWG lead in this style carries the same 13 mils of FEP as a 10 AWG lead. Against the conductor diameter, that produces a high insulation proportion — the polymer makes up a large share of the finished cross-section. Combined with the mechanical characteristics of FEP itself, which resists cold flow under sustained pressure better than softer thermoplastics, the fine sizes in this style hold up to clamping and edge contact well for their gauge. That is a different proposition from a thin-wall PVC signal wire of similar outside diameter, where both the wall and the material work against it.
24 AWG Across the Three FEP Styles
| At 24 AWG | UL 1333 (this page) | UL 1331 | UL 1330 |
|---|---|---|---|
| FEP wall | 13 mils avg / 12 mils min | 20 mils avg / 18 mils min | 20 mils avg / 18 mils min |
| Temperature | 150°C | 150°C | 200°C |
| Voltage | 300 Vac, 600 V peak tag | 600 Vac | 600 Vac |
| Finished diameter | Slimmest | Larger | Larger |
| Best suited to | Dense sensor and signal runs at 300 V class | 600 V circuits needing more wall | 600 V circuits above 150°C |
UL 1333 24 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 | 24 AWG, solid or stranded, or Litz cable magnet wire, R/C (OBMV2) rated minimum 150°C (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 |
Fine Leads in a 150°C Environment
A 24 AWG conductor carries little current, so self-heating contributes almost nothing to its operating temperature — whatever the lead reaches is essentially what the surrounding environment imposes on it. That makes fine gauges the sizes most exposed to the thermal condition of their routing path rather than to their own electrical loading, and it is why sensor and thermostat leads so often set the temperature class for an entire harness. Where those leads run through a compartment measured within 150°C, UL 1333 at 24 AWG provides the matching component recognition without the diameter of a 600 V class style. Where the same run exceeds 150°C at any point under worst-case operation, UL 1330 at 200°C is the correct style for that lead even if the rest of the harness does not need it.
Applications
Within its permitted use — internal wiring of appliances — UL 1333 24 AWG suits sensor and thermostat leads, fine signal conductors and low-current control wiring in appliances operating at 300 Vac in zones reaching 150°C, and internal electronic circuits where the 600 V peak tag applies. The slim finished diameter suits dense bundles and tight routing; the proportionally generous wall gives more clamping and edge-contact margin than the diameter implies. Litz construction is available at this gauge for fine 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 wall on a 24 AWG conductor gives a high insulation proportion
- FEP resists cold flow under sustained clamp pressure better than soft thermoplastics
- Slimmest finished diameter of the three FEP styles at this gauge
- Solid, stranded or Litz cable magnet wire conductor construction
- 300 Vac base rating with optional 600 V peak electronic use tag
- UL Recognized Component — file on record
Request a Quote
CableApex supplies UL 1333 24 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.
