UL 1331 FEP Wire Overview
UL 1331 FEP wire is a single-conductor, fluorinated ethylene propylene insulated hook-up wire for protected internal wiring in electronic and appliance equipment. The UL AWM Style 1331 reference identifies a 600 V construction rated for continuous use up to 150°C in dry conditions and up to 80°C in oil. This makes the style relevant when equipment designers need compact, heat-resistant internal wiring around power supplies, heaters, instruments and other temperature-generating components.
The style designation does not by itself confirm that every conductor size, strand construction, color or marking is available under the same approval. For an order, TEBAOFLEX reviews the requested AWG size, conductor finish, insulation color, operating environment and required printed marking before confirming the build and documentation.
UL 1331 Wire at a Glance
| Selection item | Style reference | What the buyer should confirm |
|---|---|---|
| Product type | Single-core FEP high-temperature hook-up wire | Internal wiring method and required mechanical protection |
| Rated voltage | 600 V style reference | Equipment circuit voltage and termination requirements |
| Dry temperature | 150°C style reference | Hot-spot temperature, conductor finish and terminal rating |
| Oil condition | 80°C under the UL reference | Oil type, exposure time and complete assembly suitability |
| Insulation | FEP fluoropolymer | Color, striping, identification and wall thickness |
| Conductor | Soft-annealed tinned copper reference construction | Solid, stranded or silver-plated alternative as required |
| Reference size range | 30 AWG to 4/0 | Production availability for the selected construction |
| Typical use | Electronic and appliance internal wiring | End-product standard and installation limitations |
Reference Size and Dimension Table
The following nominal values are selection references, not universal finished-wire dimensions. Outside diameter changes with conductor stranding, conductor finish, manufacturing tolerance and the approved construction. TEBAOFLEX will confirm the production dimensions for the requested wire before supply.
| AWG | Reference stranding | Insulation thickness (in) | Insulation thickness (mm) | Nominal O.D. (in) | Nominal O.D. (mm) |
|---|---|---|---|---|---|
| 30 | 7/38 | 0.020 | 0.5 | 0.052 | 1.3 |
| 28 | 7/36 | 0.020 | 0.5 | 0.055 | 1.4 |
| 28 | 19/40 | 0.020 | 0.5 | 0.055 | 1.4 |
| 26 | 7/34 | 0.020 | 0.5 | 0.063 | 1.6 |
| 26 | 19/38 | 0.020 | 0.5 | 0.063 | 1.6 |
| 24 | 7/32 | 0.020 | 0.5 | 0.067 | 1.7 |
| 24 | 19/36 | 0.020 | 0.5 | 0.067 | 1.7 |
| 22 | 7/30 | 0.020 | 0.5 | 0.074 | 1.9 |
| 22 | 19/34 | 0.020 | 0.5 | 0.074 | 1.9 |
| 20 | 7/28 | 0.020 | 0.5 | 0.081 | 2.1 |
| 20 | 19/32 | 0.020 | 0.5 | 0.081 | 2.1 |
| 18 | 7/26 | 0.020 | 0.5 | 0.091 | 2.3 |
| 18 | 19/30 | 0.020 | 0.5 | 0.091 | 2.3 |
| 16 | 26/30 | 0.020 | 0.5 | 0.097 | 2.5 |
| 14 | 19/27 | 0.020 | 0.5 | 0.111 | 2.8 |
| 14 | 41/30 | 0.020 | 0.5 | 0.109 | 2.8 |
| 12 | 19/25 | 0.020 | 0.5 | 0.132 | 3.4 |
| 12 | 37/0.0133 | 0.020 | 0.5 | 0.133 | 3.4 |
| 10 | 37/0.0167 | 0.020 | 0.5 | 0.158 | 4.0 |
| 8 | 19/0.0295 | 0.030 | 0.8 | 0.201 | 5.1 |
| 8 | 133/29 | 0.030 | 0.8 | 0.230 | 5.8 |
| 6 | 19/0.0372 | 0.030 | 0.8 | 0.241 | 6.1 |
| 6 | 133/27 | 0.030 | 0.8 | 0.273 | 6.9 |
| 4 | 133/25 | 0.030 | 0.8 | 0.325 | 8.3 |
| 2 | 133/23 | 0.030 | 0.8 | 0.395 | 10.0 |
| 1 | 259/25 | 0.045 | 1.1 | 0.462 | 11.7 |
| 1/0 | 259/24 | 0.045 | 1.1 | 0.500 | 12.7 |
| 2/0 | 259/23 | 0.045 | 1.1 | 0.555 | 14.1 |
| 4/0 | 259/21 | 0.045 | 1.1 | 0.676 | 17.2 |
Conductor and Color Options
The reference construction uses a soft-annealed tinned copper conductor. Solid copper and soft-annealed silver-plated copper may be evaluated as alternative constructions when the required termination method or operating temperature calls for a different conductor finish. The conductor option must be matched to the requested marking and documentation rather than treated as interchangeable after approval.
Common FEP insulation colors include black, brown, red, orange, yellow, green, blue, violet, gray and white. Custom colors, striping and printed identification can be reviewed against order quantity and production capability. Submit the required color code and marking text with the inquiry.
Typical Applications and Installation Limits
Typical uses include protected internal wiring in electronic equipment, household and commercial appliances, industrial instruments, control assemblies, power conversion equipment and other devices with elevated internal temperatures. The compact FEP insulation can help route conductors through space-limited equipment where a general-purpose thick-wall wire would be difficult to install.
UL 1331 is an appliance wiring material style, not a blanket approval for building wiring, unrestricted outdoor exposure, direct burial or every oil-immersed application. The equipment designer should verify the end-product standard, terminal temperature, mechanical protection, bend condition and compatibility with fluids used in the finished assembly. Where oil exposure is expected, provide the oil type, temperature and exposure duration for review.
How to Specify UL 1331 Hook-Up Wire
For an accurate construction review, provide the required AWG size, solid or stranded conductor, strand count, tinned or silver-plated finish, insulation color, printed marking, reel length, quantity and end-use equipment. Also identify the circuit voltage, maximum dry temperature and any oil exposure. A drawing or photograph of an existing wire marking is useful when the request is for replacement or cross-reference work.
For a higher-temperature FEP style, review the UL 1330 FEP hook-up wire. Projects requiring PTFE insulation can compare the UL 1213 PTFE hook-up wire and UL 1212 PTFE wire. The complete range is available under high-temperature and specialty cables.
UL 1331 FEP Wire FAQ
What is UL Style 1331 wire?
UL Style 1331 is a single-conductor FEP-insulated Appliance Wiring Material style intended for protected internal wiring in electronic and appliance equipment.
What are the UL 1331 temperature and voltage ratings?
The style reference is 600 V and 150°C for dry operation. The reference also identifies an 80°C oil condition. Final use must follow the approved construction and the requirements of the end product.
Which conductor finishes are available?
Tinned copper is the reference construction. Solid copper and silver-plated copper may be considered for construction-specific requirements, subject to confirmation of availability, marking and documentation.
What AWG range is covered by the reference table?
The source reference covers 30 AWG through 4/0, with more than one strand construction for several sizes. Actual production availability and finished dimensions must be confirmed for the selected construction.
Can TEBAOFLEX provide custom colors and printing?
Color, striping, printed identification, reel length and packaging can be reviewed against the requested quantity and technical requirements. They are not assumed to be available for every construction.
Send Your UL 1331 Wire Requirements
TEBAOFLEX can review your equipment drawing and requested wire configuration, then confirm buildable dimensions, documentation, marking and supply terms.
Technical content reviewed September 2026. Style ratings and construction-specific approval scope should be reconfirmed for the ordered wire.
