Product Description
Heat Shrink Semi-conductive / Insulation Dual Layer Tube
The heat shrink semi-conductive dual layer tube is a two-layer heat-shrinkable sleeve built for medium-voltage cable joints and terminations. The red inner layer is an insulation material that provides reliable electrical insulation, while the black outer layer is a semi-conductive material that delivers electrical shielding and stress control. Together they reproduce the screened construction of a medium-voltage cable across a joint, so the electric field is controlled exactly where the cable screen has been removed.
It is designed for medium voltage cable joints up to 42 kV, begins shrinking at 90 °C and is fully recovered at 130 °C.
If you are searching for a semi-conductive heat shrink tube for medium voltage cable joints that combines insulation and shielding in a single sleeve, this dual layer tube is the direct-fit solution.
Why a semi-conductive dual layer tube?
In a medium-voltage cable, the conductor is wrapped in insulation and then bounded by a semi-conductive screen, which smooths the electric field and prevents stress concentration at the surface. When a joint is made, that screen must be cut back - and the cut edge becomes the point of highest electrical stress in the whole circuit. If the stress is not controlled, partial discharge and surface tracking begin there.
A dual layer heat shrink tube with a red insulation inner layer and a black semiconductive outer layer solves this in a single sleeve:
The inner insulation layer re-establishes the dielectric wall over the joint.
The semi-conductive outer layer re-establishes the shielding / stress-control function, grading the field so no single point is over-stressed.
This is why the tube is specified as a heat shrink stress control tube for MV cable joints - it restores both the insulation and the screen in one operation.
Key features & benefits
True dual-layer construction - insulating inner layer + semi-conductive outer layer in one heat-shrinkable sleeve.
Electrical shielding & stress control - the semi-conductive outer layer (volume resistivity ≥ 1×10¹⁰ Ω·cm) reproduces the cable screen across the joint.
High-performance insulation - inner layer dielectric strength ≥ 20 kV/mm, volume resistivity ≥ 1×10¹⁴ Ω·cm, dielectric constant ≤ 4.
Medium-voltage rated - for cable joints and terminations up to 42 kV.
Strong, tough compound - tensile strength ≥ 10 MPa, elongation at break ≥ 350 % (both layers).
Stable after heat ageing - ≤ ±20 % change after 130 °C × 168 h.
Controlled recovery - starts at 90 °C, fully recovered at 130 °C.
Low eccentricity (≤ 30 %) and shrinkage (≤ 10 %) - consistent wall thickness and reliable fit.
Wide thermal reliability - heat shock 160 °C / 4 h, no crack; brittle temperature −40 °C.
Applications
Medium voltage cable joints and terminations (up to 42 kV)
Stress control where the cable semi-conductive screen is cut back
Joints in screened MV power cable - XLPE, EPR and PILC
Electrical shielding and field grading in joint kits and terminations
Insulation + shielding of cable cores inside joint enclosures
Technical specifications
| Spec. | As supplied ID min (mm) | As supplied wall (±20 %) | Recovered ID max (mm) | Recovered wall (±10 %) | Standard length (mm) |
|---|---|---|---|---|---|
| WDWT-30/12 | 30 | 2.8 | 12 | 5.8 | 300–1000 |
| WDWT-35/13 | 35 | 2.5 | 13 | 5.8 | 300–1000 |
| WDWT-45/17 | 45 | 2.3 | 17 | 5.8 | 300–1000 |
| WDWT-55/21 | 55 | 2.2 | 21 | 5.8 | 300–1000 |
| WDWT-65/26 | 65 | 2.3 | 26 | 5.8 | 300–1000 |
| WDWT-85/30 | 85 | 2.7 | 30 | 7.2 | 300–1000 |
| WDWT-100/38 | 100 | 2.9 | 38 | 7.2 | 300–1000 |
| WDWT-120/45 | 120 | 2.9 | 45 | 7.2 | 300–1000 |
Technical data - inner insulation layer
| Property | Test method | Standard value |
|---|---|---|
| Tensile strength | ASTM D-638 | ≥ 10 MPa |
| Elongation at break | ASTM D-638 | ≥ 350 % |
| Tensile strength variation after heat aging (130 °C × 168 h) | ASTM D-5510 | ≤ ±20 % |
| Elongation at break variation after heat aging (130 °C × 168 h) | ASTM D-5510 | ≤ ±20 % |
| Volume resistivity | IEC 60093 | ≥ 1×10¹⁴ Ω·cm |
| Dielectric strength | IEC 60243 | ≥ 20 kV/mm |
| Dielectric constant | IEC 60250 | ≤ 4 |
| Brittle temperature | ISO 974 | −40 °C |
| Hardness (Shore A) | ISO 868 | ≥ 80 |
| Heat shock | 160 °C, 4 h | No crack |
| Longitudinal shrinkage | ASTM D-2671 | ≤ 10 % |
| Eccentricity | ASTM D-2671 | ≤ 30 % |
Technical data - outer semi-conductive layer
| Property | Test method | Standard value |
|---|---|---|
| Tensile strength | ASTM D-638 | ≥ 10 MPa |
| Elongation at break | ASTM D-638 | ≥ 350 % |
| Tensile strength variation after heat aging (130 °C × 168 h) | ASTM D-5510 | ≤ ±20 % |
| Elongation at break variation after heat aging (130 °C × 168 h) | ASTM D-5510 | ≤ ±20 % |
| Volume resistivity | IEC 60093 | ≥ 1×10¹⁰ Ω·cm |
| Hardness (Shore A) | ISO 868 | ≥ 80 |
| Heat shock | 160 °C, 4 h | No crack |
| Brittle temperature | ISO 974 | −40 °C |
| Longitudinal shrinkage | ASTM D-2671 | ≤ 10 % |
| Eccentricity | ASTM D-2671 | ≤ 30 % |
How to select the right size
Measure the joint OD - the outer diameter of the insulated core or joint body to be covered.
Pick by recovered ID - recovered inner diameter must be smaller than the joint OD so the tube grips tightly (e.g. 21 mm joint → WDWT-55/21).
Check as-supplied ID - the tube must slide over the largest part of the joint before shrinking (55 mm as supplied).
Confirm recovered wall - 5.8 mm for WDWT-30/12 to WDWT-65/26; 7.2 mm for the larger WDWT-85/30 to WDWT-120/45.
Choose length - standard 300–1000 mm; custom lengths available on request.
Product display
Certificate
FAQ
Q: What is a semi-conductive heat shrink dual layer tube used for? A: It insulates and re-screens medium-voltage cable joints. The inner layer insulates; the semi-conductive outer layer provides electrical shielding and stress control where the cable screen is cut back. It is used in medium voltage cable joints up to 42 kV.
Q: What are the two layers made of? A: The red inner layer is insulation material for electrical insulation; the black outer layer is semi-conductive material for electrical shielding.
Q: What is the difference between the inner and outer layer resistivity? A: The inner insulation layer has a volume resistivity of ≥ 1×10¹⁴ Ω·cm (an insulator), while the outer semi-conductive layer is ≥ 1×10¹⁰ Ω·cm - lower by design so it conducts and grades the field like a cable screen.
Q: What voltage is it rated for? A: Medium voltage cable joints up to 42 kV.
Q: What is the shrink temperature? A: Shrinking starts at 90 °C and the tube is fully recovered at 130 °C.
Q: What sizes are available? A: 8 standard specs from WDWT-30/12 (recovers to 12 mm ID, 5.8 mm wall) up to WDWT-120/45 (recovers to 45 mm ID, 7.2 mm wall).
Q: Is it a stress control tube for MV cable joints? A: Yes - the semi-conductive outer layer performs the stress-control / shielding function, making it a heat shrink stress control tube for MV cable joints and terminations.
Q: How is it supplied? A: Standard lengths of 300–1000 mm. Custom cut lengths available on request.
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