Fiberglass Sleeving Temperature Rating Guide

Published temperature classes are tied to defined tests. Real assemblies add conductor heating, ambient temperature, thermal cycling, fluids, bending and local hot spots.

Document continuous temperature, peak temperature and duration separately. If sleeving is part of the primary insulation system, confirm dielectric withstand and system requirements independently.

1. Map the heat profile. Record ambient temperature, conductor rise, continuous operating temperature, maximum peak temperature and peak duration. Measure near terminals and bends, where hot spots usually appear.
2. Define the electrical duty. List working voltage, transient voltage, frequency, creepage or clearance limits and whether the sleeve is supplementary or primary insulation. The required dielectric test belongs to the complete assembly.
3. Choose the construction direction. Start with acrylic for moderate heat, silicone resin for higher thermal margin and dimensional stability, or silicone rubber when flexibility and vibration dominate. Do not select by coating name alone.
4. Size the sleeve after installation is understood. Share conductor bundle diameter, terminal geometry, flare allowance, wall build, tolerance and cut length. A sleeve that is too tight can split or reduce coverage; one that is too loose can move during crimping.
5. Screen the environment. Identify oil, coolant, cleaning agents, humidity, salt spray, abrasion, sharp edges, vibration and repeated bending. Ask for a compatibility check whenever the project includes a new fluid or adhesive.
6. Validate representative samples. Install the proposed sleeve using the production process, then run thermal cycling, dielectric withstand, insulation resistance, abrasion, bend and visual coverage checks. Record failures and adjust the construction before volume release.

Consider a motor lead routed beside an inverter housing. The first request says only “fiberglass sleeve, 200°C, UL required”. That request leaves too many decisions open: the measured conductor rise is unknown, the peak duration is missing, the sleeve may be primary or supplementary insulation, and the bend near the terminal is not described. A supplier can quote a nominal product, but the engineering team still cannot judge whether it will survive installation or service.

After measurement, the same request becomes actionable: 142°C continuous at the bundle, 188°C for 20 minutes during an overload event, 600 V working voltage, 8.4–9.1 mm bundle diameter, a 12 mm minimum bend radius, silicone oil splash, and a 2,000-hour thermal-cycle target. The drawing also shows a 35 mm flared section over the terminal and a requirement that no braid remain exposed after crimping. Those details point toward a flexible silicone-rubber or silicone-resin construction with controlled expansion, a defined cut length and an installation check at the flare.

The sample plan then has a clear pass/fail path: inspect the minimum wall and coverage, install five pieces with the production crimp, record pull or movement after vibration, cycle between ambient and the measured peak, apply the specified dielectric test, and inspect for cracking, whitening, delamination or exposed braid. If the sleeve passes electrically but creeps toward the terminal, the solution is not simply a higher temperature grade; it may require a different diameter, end treatment or routing restraint. This is why the heat curve, geometry and process belong in the first RFQ.

A good approval package connects the drawing to evidence. Keep the material construction, nominal and tolerance dimensions, colour, lot, production process, test method, conditioning and acceptance criteria in one controlled record. Include photos of the installed sleeve before and after thermal cycling so movement, cracking, whitening, exposed braid or loss of coverage can be reviewed quickly.

For a motor or transformer lead, the minimum practical package normally includes dimensional inspection, installation confirmation, dielectric withstand, insulation resistance, thermal ageing or cycling, bend or vibration exposure, and a visual check of every termination. For a liquid-cooling or fluid-adjacent harness, add the project fluid, concentration, temperature and immersion or splash duration. If the part is safety-related, align the test plan with the customer standard before samples are built.

WCW can review a drawing, imported part number, sample or failed test report and return a recommendation with the information still missing. The fastest RFQ includes the heat curve, voltage, bundle diameter, target approval, fluid list, estimated annual demand and required sample date.