Quick answer: Choose high-temperature wire according to the temperature at its installed location, the required electrical performance and the way it will be terminated. Silicone, silicone/fiberglass-braided and fluoropolymer-insulated wires can serve different high-temperature applications. A wire rated for 200°C does not make the complete wire harness suitable for 200°C operation. The connector housing, crimp terminal, heat-shrink tubing, protective sleeve and nearby components must also be checked against their own specifications and actual service temperatures.
For an OEM buyer, the useful question is: What will each part of the assembly experience in service, and is the specified combination suitable? This guide explains how to turn that question into a manufacturing drawing and an actionable RFQ.
1. Define the Temperature at Each Location
A wire harness may run from a hot appliance compartment to a cooler control board. Different sections can require different materials, even when the wires belong to the same circuit.
Before selecting insulation, define:
- Continuous temperature: Expected temperature at the wire, connector and termination locations during normal operation.
- Peak exposure: Maximum anticipated temperature, its duration and frequency.
- Electrical duty: Voltage, current, conductor size and relevant insulation requirements.
- Mechanical duty: Fixed installation, movement, repeated bending, abrasion and strain relief.
- Other exposure: Oils, cleaning agents, humidity, sharp edges and nearby surfaces.
- Space constraints: Wire outside diameter, bend radius, sleeve clearance and connector location.
Measure or validate temperatures at relevant assembly locations when the thermal profile is uncertain. Air temperature near a heater, conductor temperature under load and housing temperature at the mating interface may all differ.
2. Compare High-Temperature Wire Insulation Materials
The table below is a selection guide. Verify each candidate against the exact approved wire datasheet, including its temperature, voltage, dimensions and permitted use.
| Insulation construction | When buyers consider it | What to verify before ordering |
|---|---|---|
| PVC hook-up wire | Protected internal wiring within the selected style's operating limits | UL style, temperature/voltage rating, insulation thickness, finished diameter and terminal fit |
| Silicone rubber wire | Elevated temperatures where flexibility is important | Specific silicone formulation, mechanical protection, bend conditions and stripping/crimping compatibility |
| Silicone wire with fiberglass braid | Hot appliance zones where a specified silicone-insulated, braided construction is useful | Whether the braid is an outer covering, braid finish, wire OD, abrasion behavior and how the end will be prepared |
| FEP fluoropolymer wire | Applications needing a qualified combination of thermal, chemical and dimensional properties | Exact FEP grade/style, temperature and voltage rating, insulation diameter and approved processing method |
| PTFE fluoropolymer wire | Applications where its particular thermal and chemical properties are specified | Exact construction and rating, availability, wire preparation and termination fit |
Silicone and fluoropolymers are different material families; FEP and PTFE should not be treated as the same insulation. A fiberglass braid is also not, by itself, a universal thermal upgrade. The complete wire construction determines the relevant rating.
3. Six UL Wire Styles Buyers Commonly Encounter
UL style numbers are useful starting points for identifying a wire construction. They do not replace the purchased manufacturer's full part number, drawing revision or datasheet.
| Wire style | Representative insulation / construction | Published example rating | Selection note |
|---|---|---|---|
| UL1007 | PVC hook-up wire | 80°C, 300 V | Check outside diameter and termination fit |
| UL1015 | PVC hook-up wire | 105°C, 600 V | Often thicker than a comparable UL1007 construction; not a drop-in replacement |
| UL3122 | Silicone insulation with fiberglass braid | 200°C, 300 V | Verify the specific braided construction and termination method |
| UL3135 | Silicone rubber insulation | 200°C, 600 V | Check insulation OD, flexibility and approved crimp arrangements |
| UL1332 | FEP-insulated wire | 200°C, 300 V | FEP construction; do not label it PTFE |
| UL3239 | High-voltage silicone-insulated wire | Varies by approved construction | Check actual manufacturer rating and voltage class; do not assign one universal temperature or voltage |
The ratings above are based on published wire specifications. Actual ratings depend on the selected wire manufacturer and part number. The temperature rating of a wire does not determine the rating of the complete harness.
Published wire specifications from Tong Wu and Top Cable illustrate differences in these constructions. Top Cable also provides a separate UL1332 FEP reference. These are supplier examples; confirm the exact approved part before ordering.
Two wires with the same AWG can have different overall diameters because their insulation systems differ. That difference matters at the terminal's insulation support, connector rear entry, sleeving and routing points.
4. Why a 200°C Wire Does Not Mean a 200°C Harness
Consider a harness that runs from a warm control area toward a heating element. The wire supplier may rate one section's insulation for 200°C, while the mating connector or heat-shrink tubing has a lower approved continuous operating temperature.
A useful engineering review looks at the conditions of every component where it is installed:
| Assembly element | What the drawing or BOM should identify | Why it matters |
|---|---|---|
| Wire in the hot zone | Exact wire style and material; continuous and peak exposure | Determines suitability of the selected insulation construction |
| Wire in the cooler zone | Exact wire style and local temperature | A different insulation may be suitable away from the heat source |
| Connector housing | Full housing and mating-part numbers; approved operating range | Housing materials and interfaces may impose a lower local limit |
| Crimp terminal | Approved terminal, conductor/insulation range and applicable temperature conditions | Correct wire fit alone does not confirm mechanical and thermal suitability |
| Heat-shrink tubing | Material, size, adhesive where applicable and continuous-use rating | Shrink temperature is not the same as continuous service temperature |
| Fiberglass sleeve or other protection | Exact part, length, location and applicable ratings | Protective coverage does not automatically upgrade the underlying component |
| Soldered joint or electrical component | Approved component and termination requirements | Local temperature and mechanical support can affect reliability |
Illustrative case: A 200°C-rated wire routed into a connector that is approved for a lower operating temperature cannot be assumed to operate at 200°C at that connector. The connector-end temperature must stay within the approved limits of the actual parts. This example contains no claim about a specific Shengxin assembly or a fixed connector temperature rating.
A component with a lower rating does not necessarily prohibit its use elsewhere on the harness: the actual local temperature matters. The goal is to validate the temperature exposure by zone, then check every component in that zone.
5. What We See on Real Customer Drawings
In a review of more than 2,400 wire harness drawings—a portion of our factory's drawing archive—high-temperature wire styles such as UL3239, UL1332 (FEP), UL3122 and UL3135 appeared on several hundred drawings. The connector housings most often paired with them were common 2.0 mm, 2.5 mm and 3.96 mm pitch wire-to-board housings (XH-Type, PH-Type and VH-Type) and SM-Type wire-to-wire housings.
That combination is normal, but it illustrates the point above: at the connector end, the housing—not the wire—often sets the practical temperature limit. Check the housing manufacturer's rated operating temperature, which for many common nylon housings is well below the rating of a silicone or FEP wire.
Fewer than 1% of those drawings stated a temperature value at all. Most specified the wire only by UL style, gauge and color, so a buyer must consult the actual approved wire specification to establish its rated temperature rather than assume the drawing defines the complete assembly rating. Protective parts were usually called out by size: fiberglass sleeving, for example, typically appeared as a color, voltage class and diameter (such as a white 1.5 kV sleeve of 5–10 mm), and heat-shrink tubing by diameter and cut length.
If your application has a specific temperature requirement, state it on the drawing and identify the locations it applies to.
6. The Hidden Constraint: Heat-Shrink Tubing and Insulation Diameter
Heat-shrink tubing often appears on drawings as a diameter or a short callout without a complete material specification. That can leave the manufacturer unable to confirm its operating temperature, shrink characteristics and position.
For each section of tubing, define the material or approved part number, expanded/recovered diameter as relevant, placement, finished coverage and continuous-use temperature rating. If it protects a solder joint or breakout, define the covered area and the required inspection method.
The same discipline applies when replacing a PVC wire with silicone or fiberglass-braided wire. An identical conductor size does not mean an identical insulation outside diameter. The new construction may affect the terminal's insulation crimp, connector entry, sleeve clearance, bend radius or process tooling.
A wire substitution should not be approved solely because the conductor sizes match or the replacement has a higher advertised temperature rating. Confirm dimensional and termination compatibility, then obtain customer approval for any change to the controlled specification.
7. Examples Relevant to Shengxin's Build-to-Drawing Work
Shengxin's published product range includes assemblies described with high-temperature silicone/fiberglass wire, fiberglass sleeving and electrical protection components. These illustrate the types of construction details that a drawing may need to identify, rather than a universal temperature rating for the finished harness.
Depending on the drawing, the manufacturing review may cover combinations such as:
- A silicone/fiberglass wire assembly calls for the exact wire style, finished diameter, cut and strip dimensions, and applicable termination details.
- A sleeved connector harness calls for the sleeve material, position and coverage, as well as the housing, terminal and mating interface.
- A harness incorporating a thermal fuse or current fuse requires the correct component part number, electrical function, approved connection method and relevant temperature conditions. A fuse rating is not the harness's overall temperature rating.
Examples of these assembly forms on our site include the high-temperature silicone fiberglass wire harness, the PH-Type 2.0 mm 7-pin fiberglass-sleeved wire harness, the XH-Type 2.54 mm 5-pin to JC25 sleeved wire harness built with UL1332 FEP wire, and the wire harness with thermal fuse and current fuse. For preparing a drawing or reference sample, use the project preparation guide.
For a specific OEM project, Shengxin manufactures to customer drawings or reference samples, reviews the provided manufacturing details and flags unclear material or termination requirements for clarification. The customer approves material substitutions and any change to the agreed specification.
8. High-Temperature Wire Harness RFQ Checklist
A useful RFQ separates required operating conditions from proposed material choices. Start with the details you have and mark unresolved items TBC (to be confirmed).
| RFQ field | What to provide |
|---|---|
| Thermal profile | Continuous and peak temperature by harness zone, including duration and validation requirements |
| Electrical duty | Voltage, current, circuits and applicable electrical criteria |
| Wire | Full supplier part number or UL style, conductor gauge (AWG/mm²), insulation system, color and OD |
| Connector and terminal | Housing, terminal and mating-part numbers or identification samples/photos |
| Protective parts | Heat-shrink tubing, fiberglass sleeve, ties and any adhesives: material, location and rating |
| Drawing | Length datums, branches, end treatment, pinout, tolerances and revision |
| Verification | Agreed electrical, visual, mechanical or thermal inspection and acceptance criteria |
| Commercial details | Sample quantity, estimated production quantity and requested schedule |
| Open questions | Parts, ratings or dimensions marked TBC and who will approve the resolution |
An incomplete drawing can still start a manufacturing review. A connector photo, existing sample or partial BOM helps identify what needs clarification before quotation and sampling.
9. Frequently Asked Questions
What is the best insulation for a high-temperature wire harness?
There is no universal choice. Match the selected wire's construction to the actual temperature, electrical duty, movement, chemical exposure and termination requirements. Silicone, fiberglass-braided silicone and FEP can solve different problems.
Is UL3122 wire rated for 200°C?
Published UL3122 supplier constructions commonly list 200°C and 300 V. Verify the exact purchased wire and its current documentation. That wire rating does not rate the whole harness.
Is UL1332 FEP or PTFE?
Published UL1332 examples use FEP insulation. FEP and PTFE are distinct fluoropolymers; check the manufacturer's exact specification rather than using “Teflon” as a substitute for a material name.
Does fiberglass sleeving make the entire assembly heat-resistant?
No. The sleeve has its own specified capabilities. The wire, connector, terminal, tubing and surrounding installation remain subject to their respective limits.
Can UL1015 replace UL1007 if it has a higher temperature rating?
Only after checking the approved requirements, including insulation diameter, terminal fit, voltage and temperature conditions, and customer authorization. A higher advertised rating alone is insufficient.
What if I know the heater temperature but not the connector temperature?
Identify the connector location and the expected local conditions, then agree on how to measure or otherwise validate them. Do not assume the connector experiences the same temperature as the heating element—or the cooler ambient air.
Send Shengxin Your Drawing and Temperature Requirements
A high-temperature wire harness specification should identify the actual operating zones, the selected wire construction and the temperature-sensitive parts at each termination. A clear drawing makes the manufacturing review faster and reduces avoidable material substitutions.
Share your drawing, BOM, photos or reference sample and the temperatures you need the assembly to withstand. Partial information is enough to begin the discussion. Use our Request a Quote form; we can identify open manufacturing questions and confirm the required details with you before sampling and quotation.
