Stress Control Tube Installation: 6 Steps
Six steps in order, with the mistakes that turn up in the field. Most stress control tube failures we are asked about trace back to one of them, and the sequence error is the most expensive.
The six steps
- Prepare the cable exactly to the kit drawing. Cut-back lengths differ by cable type and voltage class.
- Smooth the semicon cut. Any step or roughness at the cut concentrates the field.
- Clean and dry the insulation. Wipe with the solvent the kit specifies and let it flash off completely.
- Mark the cut-back line and slide the tube on before the joint is made.
- Position the tube on the mark so it covers the semicon cut by 10 mm to 15 mm, then confirm the extension against the data sheet.
- Recover with a swept heat source from the centre outward, then re-check position and appearance before the outer tubes go on.
What each mistake looks like
| Mistake | What you see | Cause | Fix |
|---|---|---|---|
| Heating from one end | One end recovered, the other still thick | Heat applied at a point | Sweep from the centre outward |
| Overheating one spot | Glossy or scorched patch | Heat source held too close | Keep the source moving and watch the surface |
| Tube off the cut-back line | Bare insulation or semicon visible at the cut | Position not marked | Mark the line and re-check after recovery |
| Wrinkled recovered wall | Folds along the tube | Uneven heating or a void | Re-do the tube, do not press the fold flat |
| Tube slips on the core | Tube rotates or slides after recovery | Sized on cable OD instead of the prepared insulation diameter | Re-size and replace |
| Water in the termination | Moisture at the cut | Work in damp conditions, ends not sealed | Follow the kit sealing sequence and work dry |
Work conditions matter
Damp air, dust and wind all show up in the finished termination. A tube recovered over a wet insulation surface traps water at the interface, and that water finds the cut. Check the weather and the enclosure before you start, and cover the prepared surfaces while the rest of the joint is assembled.
The sequence error that costs the most
The tube goes on before the joint is made. Once the connector is crimped, a slip-on tube cannot pass it, and the joint has to come apart. This single sequencing mistake re-works the whole termination, so treat the order in the kit drawing as fixed.
The heat settings and sweep pattern for cross-linked components are the same ones used elsewhere in the kit, covered in our heat shrink tubing installation guide. Voltage classes and kit types are listed in MV cable accessories by voltage.
What to send
Send the cable voltage class, cross-section, prepared insulation diameter and the joint type. We return the kit component, its position dimension and the recovery sequence for it.
Frequently asked questions
Which direction do I apply heat?
Sweep from the centre of the tube outward. Heating at one end can drive the tube along the core before it recovers, and leaves the other end thick.
The tube wrinkled. Can I press it flat?
No. A wrinkle in a recovered tube is a void, and pressing it does not remove the void. Cut the tube away and fit a new one.
How far should the tube cover the semicon cut?
10 mm to 15 mm over the cut, with the extension past the cut set by the voltage class. Both dimensions come from the kit drawing and the data sheet.
Can I install it in damp weather?
Only with protection over the prepared surfaces. Water trapped at the interface between the insulation and the tube is a discharge path, and the tube seals nothing by itself.
What happens if I make the joint first?
The tube has to be on the cable before the connector is crimped. After that it cannot pass the connector, so the joint has to be taken apart.