MV cable termination: step-by-step instructions and installation solutions 

MV cable termination is not a chore, but a critical operation. One incorrect millimeter of insulation cut, temperature mismatch during shrinkage, missed degreasing step - and after 6–12 months local overheating, breakdown, and emergency shutdown occurs. We have conducted 37 field audits at energy supply companies in the CIS over the past two years. In 68% of cases, failures of end seals are not related to the quality of the product, but to a violation of the installation technology.

Why “step by step” is not an instruction, but a system of conditions

The GOST R 50571.15-97 standard requires that the termination of the MV cable ensures an electrical strength of at least 120% of the rated network voltage. But in reality, the parameter depends on three interconnected layers:

• Cable preparation: surface cleanliness, cut geometry, absence of microcracks in insulation;
• Component Compatibility: type of coupling (thermo- or cold-shrinkable), voltage class, core material (copper/aluminium), screen design;

• Climatic and mechanical conditions: temperature difference from –40 °C to +50 °C, vibration on power line supports, UV load in open areas.

That is why at Shijiazhuang Hist Electric LLC, when selecting solutions for MV cable termination, we start not with a catalog, but with an analysis of the installation location: altitude above sea level, frequency of lightning discharges, presence of aggressive emissions (for example, near chemical plants). This is the only way to formulate the technical specifications for selecting a coupling - for example, a heat-shrinkable end seal of the seriesHTE-10for 10 kV cables with copper core and PE insulation or cold-shrinkable modelHC-1for 1 kV networks in conditions of high humidity.

Six steps where 9 out of 10 crews make mistakes

Based on tests in our electrical laboratory (up to 1000 kV) and data from 14 sites in Kazakhstan, Belarus and Russia, we have identified key risk points:

• Cable cutting: permissible cutting angle - no more than 5°. At an angle >8°, a zone of electric field concentration is created. We use special guide templates - they reduce the error to 0.3 mm.

• Removing the outer shell: strictly according to the size specified in the coupling passport. Overlapping the protective layer by 2–3 mm is the cause of corrosion of the aluminum screen.

• Processing of the semiconducting layer: not just a cut, but a chamfer with control of the thickness of the residual layer - 0.2–0.3 mm. Otherwise - through breakdown when testing 25 kV/min.

• Installing the Contact Tip: The crimping pressure should be 12–14 kN for copper conductors Ø150 mm². Less - heating; more - deformation of the vein.

• Shrinkage of thermoelements: surface temperature - 110–120 °C, holding time - 3 minutes. Using a gas burner without a temperature sensor causes overheating in 32% of cases.

• Final sealing: two-component silicone sealant is applied only after complete cooling. Early application - bubbles, delamination, moisture penetration.

What to do if there is no access to a laboratory?

Not all customers can carry out comprehensive tests. We have implemented a “field control” system: each end seal kit includes a QR code that leads to a page with video installation instructions for that specific model. There is also an interactive diagram for checking the cut geometry, a table of permissible deviations and a checklist for the responsible installer. It's not a lab replacement, but it reduces the chance of error by 74% - 2023 internal audit data.

Termination of a CH cable is not the end, but the beginning of a cycle

Properly performed termination lasts 25–30 years. But the service life is determined not only by the first day of installation, but by constant monitoring: inspection of tightness every 6 months, measurement of insulation resistance once a year, visual assessment of the condition of the silicone case at temperatures above +35 °C. Our couplings are designed with this in mind: they have thermal aging zone markings, contrasting color marks for quick diagnostics, and a reinforced UV-stabilized elastomer composition.

MV cable termination is not a set of actions. This is a solution that lives in a specific environment, under load, in real time. Selecting a component is the first step. Its proper use is the second. And support at all stages is the third. This is exactly how Shijiazhuang Hist Electric LLC works: not a seller, but a partner in ensuring network continuity.