UL 1333 FEP Appliance Wire 18 AWG — One Wall Thickness Across the Whole 30 to 10 AWG Range
UL 1333 in 18 AWG is a single-conductor appliance wiring material with extruded FEP insulation, rated 150°C maximum at 300 Vac with a horizontal flame rating. Unlike UL 1330 and UL 1331, which each specify three wall brackets that step up with conductor size, UL 1333 specifies one figure for its entire range: 13 mils minimum average thickness, 12 mils minimum at any point, from 30 AWG through 10 AWG. At 18 AWG that means the same wall as a 30 AWG signal conductor and the same wall as a 10 AWG power lead. CableApex supplies UL 1333 18 AWG as a UL Recognized Component — file on record.
What a Constant Wall Means at Different Gauges
When insulation thickness does not scale with conductor size, the ratio between wall and conductor changes continuously across the range. At the fine end, 13 mils of FEP on a 30 AWG conductor is generous in proportion — the insulation dominates the cross-section and the wire tolerates handling, clamp pressure and edge contact well for its diameter. At 18 AWG the proportion is balanced: enough wall for the mechanical demands of a routed appliance lead, without the diameter penalty of a bracket-scaled style. Toward 10 AWG the same 13 mils becomes proportionally lean around a much larger conductor, which keeps the finished diameter compact but leaves less margin for abrasion, making the optional covering more worth considering at the heavy end than at the fine end.
The practical consequence for a design is that gauge can be changed within this style without recalculating insulation dimensions from a bracket table. A circuit revised from 20 AWG to 18 AWG, or from 18 AWG to 16 AWG, keeps the same wall figure and the finished diameter changes only by the conductor difference. In a style with brackets, the same revision can cross a boundary and change the wall unexpectedly.
Constant 13-mil Wall Across the Range
| Conductor size | FEP wall | Wall relative to conductor | Practical note |
|---|---|---|---|
| 30–24 AWG | 13 mils avg / 12 mils min | Generous | Robust for gauge; covering rarely needed |
| 22–16 AWG (18 AWG here) | 13 mils avg / 12 mils min | Balanced | Compact diameter for routed appliance leads |
| 14–10 AWG | 13 mils avg / 12 mils min | Lean | Consider covering where abrasion is a factor |
UL 1333 18 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 | 18 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 — uniform across the full conductor range |
| 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 |
Where the Covering Options Earn Their Place
Because the base wall does not increase with gauge, the two covering options carry more weight in this style than in a bracket-scaled one. An extruded FEP covering at 10 mils minimum at any point roughly doubles the fluoropolymer around the conductor, which restores a substantial abrasion margin while keeping the smooth low-friction outer surface that helps the lead pull through passages. A glass braid at 7 mils minimum takes a different approach, presenting a fibrous outer face that wears sacrificially and stands up to contact with hot metalwork better than a smooth polymer surface, at the cost of higher pull friction. At 18 AWG in a clean routed harness neither is usually necessary; where the lead runs against a bracket edge or through a compartment opened during service, one of them generally is.
Applications
Within its permitted use — internal wiring of appliances — UL 1333 18 AWG suits routed internal leads, control and light-duty power connections in appliances operating at 300 Vac in zones reaching 150°C, and internal electronic circuits where the 600 V peak tag applies. The constant wall makes it straightforward to specify across several gauges in one harness without tracking bracket boundaries. Litz construction is available for high-frequency winding leads at this gauge. 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
- One wall figure across 30–10 AWG — no bracket table to track
- Gauge revisions within the style do not change the insulation dimension
- 13 mils wall at 18 AWG gives a compact diameter for routed appliance leads
- Covering options restore abrasion margin where the run demands it
- 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 18 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.
Other UL 1333 sizes: 20 AWG · 22 AWG · UL 1331 FEP Wire (150°C / 600 Vac)
