Insulation sleeving is a flexible tube that electrically insulates a conductor, a solder joint or a terminal and, depending on the material, also protects it from heat. For hot environments, silicone, glass fibre and silicone-coated glass fibre sleevings are among the most important types. Silicone sleeving withstands about 180 degrees continuously, silicone-coated glass fibre up to around 200 degrees, plain glass fibre even more depending on the finish. The choice follows continuous temperature, required dielectric strength, mechanical load and inner diameter. The wrong sleeving risks embrittlement, creepage currents or a tube that no longer slides on.
What insulation sleeving is
Insulation sleeving encloses a conductor or component and separates it electrically from its surroundings. Unlike fixed cable insulation, it is fitted afterwards, usually over solder joints, winding ends, terminal lugs or bare wires. It increases creepage and clearance distances, guards against contact and, depending on the material, withstands high temperatures. In transformers, motors, heaters and switch cabinets it sits exactly where the standard insulation is not enough. The basics of thermal capability are covered in the article on high-temperature insulation.
Types of insulation sleeving
The material determines temperature capability, flexibility and price. For purchasing it pays to keep the families clearly apart.
- Silicone sleeving: extruded solid silicone tube, very flexible, permanently elastic, good dielectric strength. Thermal class H, around 180 degrees continuous, more for short periods.
- Glass fibre sleeving: braided glass fibre, often impregnated with varnish or resin. High temperature capability, but on its own low dielectric strength, so mostly coated.
- Silicone-coated glass fibre sleeving: glass fibre braid with a silicone coating. Combines the heat resistance of glass fibre with the dielectric strength of silicone, up to about 200 degrees.
- Acrylic-coated glass fibre sleeving: cheaper variant with an acrylic resin coating, thermal class F, around 155 degrees, for moderate temperatures.
- PTFE sleeving: chemically almost inert, very high temperature capability above 250 degrees, expensive and stiffer, for aggressive media and extreme conditions.
- Heat-shrink sleeving: shrinks onto the conductor under heat and then sits tight. For defined insulation and strain relief, usually up to 125 or 135 degrees, more for high-temperature types.
Temperature and thermal classes
The continuous temperature of a sleeving follows the thermal classes of electrical insulating materials. These classes define which temperature a material withstands over its planned service life without losing its insulating effect. Details are in the article on insulation material classes.
- Class F: up to 155 degrees, typical for acrylic-coated glass fibre sleeving.
- Class H: up to 180 degrees, typical for silicone sleeving.
- Class H and above: up to around 200 degrees, silicone-coated glass fibre.
- Above 200 degrees: PTFE and plain, well impregnated glass fibre.
Short-term capability often exceeds the continuous rating. What matters for the design is the continuous temperature at the hottest point, not the peak value in the data sheet.
Applications
Insulation sleeving sits where conductors run bare or where the existing insulation cannot stand the temperature.
- Windings in motors and transformers: insulation of winding ends and connections, often combined with mica tape and impregnating resin.
- Connecting leads and terminal lugs: protection against contact and short circuit.
- Solder and connection points: added insulation after soldering, often with heat-shrink sleeving.
- Heaters and lighting: silicone and glass fibre sleeving close to heat sources.
- Cable harnesses: mechanical and thermal protection, in addition to the actual cable insulation.
Selection criteria
Five variables decide which sleeving fits. Clarifying them before the request saves sampling loops.
- Continuous temperature at the hottest point, which sets the thermal class.
- Dielectric strength and operating voltage, which set the wall thickness.
- Inner diameter to match the conductor, with a little allowance for fitting.
- Mechanical load: abrasion, bending, vibration.
- Chemical load: oil, solvents, aggressive media, where PTFE often leads.
For switchgear and oil-filled equipment we recommend silicone-coated glass fibre sleeving, because it is heat resistant and dielectrically strong at the same time. Plain glass fibre without a coating belongs only where dielectric strength is secured by other insulating layers.
Conversion and cutting at GOBA
Insulation sleeving is rarely installed in full roll length. GOBA cuts sleeving to the length you need, with tight tolerances and clean cut edges so the tube slides on without fraying. We convert silicone, glass fibre, silicone-coated glass fibre and PTFE sleeving to drawing, also in small lots and mixed packs of different lengths. On request we supply bundled, marked and sorted ready for assembly. Since 1959 GOBA has processed electrical insulating materials and knows how they behave when cut, for example that silicone needs a different blade guidance than impregnated glass fibre.
GOBA Takeaway
The right insulation sleeving is decided by continuous temperature and required dielectric strength, not by the list price per metre. For hot applications, silicone and silicone-coated glass fibre lead, for extreme temperatures and aggressive media, PTFE. GOBA supplies the matching sleeving as insulation materials and converts it to your size, up to ready-to-fit insulation and molded parts. Send us material, inner diameter, length and quantity, and you will receive a technical quote.
