How to Make a Cable Joint?
Potting with Polyurethane Resin
Cable joints are among the most critical points in electrical distribution systems. This guide covers every step — from preparing the joint to curing the resin fill — along with practical tips and safety warnings.
Contents
Why Is Resin Potting Important in Cable Joints?
Cable joint points are exposed to moisture ingress, mechanical vibration, temperature changes and chemical contamination. Without adequate insulation, the following problems arise:
- Moisture accumulation and corrosion at the joint
- Increased risk of arcing or short circuit
- Long-term degradation of transmission quality
- Rising maintenance and repair costs
Proper resin potting aims to make the joint fully watertight, eliminating all of these risks.
Which Resin System Should Be Used?
The system is chosen based on whether the application is permanent or requires service access.
| System Type | Characteristic | Suitable Application |
|---|---|---|
| Rigid Polyurethane (Protolin) | High mechanical strength, permanent protection | Permanent underground or duct applications |
| Elastic / Removable (NCflex W-25) | Service access, maintenance-friendly, elastic | Re-enterable connection points |
| Gel-Type (NCflex W-30) | Probe-measurable, soft structure | Field connections requiring measurement |
| Silicone Gel (NCgel) | Transparent, low mechanical stress | Enclosures and sensitive electronics |
Safety Before You Begin
Pre-Application Preparation
Step-by-Step Cable Joint Potting
The steps below describe a general application flow. The specific instructions in your product’s TDS take priority.
Prepare the Cable and Join the Conductors
Strip the cable ends per the manufacturer’s instructions. Connect the conductors mechanically and electrically using a suitable joint sleeve/connector. Ensure the connection is solid and clean.
Position the Enclosure / Mould
Place the enclosure or mould around the joint. Seal any gaps where resin could leak. Ensure the mould is centred so it fully surrounds the joint.
Measure Components A and B
Measure the components at the ratio the system requires. Verify from the TDS whether the ratio is volumetric or gravimetric — they are not the same. Use calibrated measuring tools.
Mix Until Homogeneous
Mix the components until colour and consistency are homogeneous. Scrape the container walls and base to avoid unmixed material. Move to the next step before pot life expires.
Pour Slowly
Pour the mix slowly from one side of the enclosure. Fast pouring traps air and creates bubbles. Let the resin flow under its own weight to fill all voids.
Wait for Curing and Inspect
Initial set typically occurs in 30–90 minutes depending on the system; full cure may take longer. Do not apply mechanical load to the joint before curing completes. Check the surface for bubbles, cracks or tackiness.
Common Mistakes
- Application on wet/dirty surfaces: Isocyanate reacts with moisture to produce CO₂ → foaming and bubbles.
- Estimating the ratio by eye: Mixing without measuring causes cure problems.
- Incomplete mixing: Unmixed material on the container walls creates soft/sticky patches.
- Exceeding pot life: Late-poured mix won’t flow properly and leaves voids.
- Application at low temperature: Below 10°C, curing slows or fails to complete.
Easy Field Application with the NCpack Pouch System
The NCpack dual-component pouch system eliminates the measuring and mixing steps above. Components A and B are kept separate by an internal barrier in a single pouch; when pressure is applied, the barrier opens and the components mix inside the pouch. No extra container, scale or mixer is needed — ratio error and moisture contact risk are minimised in field conditions.
Let’s Determine the Right System for Your Application
Share your cable type, environmental conditions and service requirements; we’ll help you decide between rigid resin, NCflex or NCgel. Contact us to request a sample.