MV Cable Termination Types: Heat-Shrink, Cold-Shrink and Push-On Compared

An MV cable termination is the engineered interface at the end of a medium-voltage power cable that controls electrical stress, seals out moisture, and provides a safe mechanical and electrical connection to switchgear, transformers, or overhead lines — the three dominant technologies used to build this interface are heat-shrink, cold-shrink, and push-on (slip-on) terminations. This guide explains the underlying electrical-stress-control physics, how to size and select a termination class for a given cable and voltage, walks through a worked example of calculating the maximum operating stress at the cable screen cut-back point, and compares the three technologies against installation, environmental, and maintenance criteria relevant to buyers across the Middle East and Gulf region (including Egypt and Saudi Arabia), North Africa, the CIS, and Sub-Saharan Africa.

Choosing the wrong termination type is one of the most common root causes of MV cable failures in the field — not because the cable itself is deficient, but because uncontrolled electrical stress at the screen cut-back point initiates partial discharge, tracking, and eventual flashover. Understanding the stress-control method behind each termination family lets engineers select correctly rather than by habit or price alone.

Why Termination Design Matters: The Electrical Stress Problem

Inside a shielded MV cable, the semiconducting screen keeps the electric field radially symmetric around the conductor. The moment that screen is cut back to expose insulation for the termination, the field lines are no longer confined — they concentrate sharply at the screen cut-off edge. This localized stress can be many times higher than the bulk stress in the cable insulation, and if left uncontrolled it will initiate partial discharge activity, erosion, and eventual dielectric breakdown.

All three termination technologies exist to solve this one problem, using two alternative approaches:

• Geometric (stress-cone) control — physically increasing the insulation thickness and radius at the cut-back point to spread the field over a larger volume, lowering the local gradient.
• Capacitive (stress-control tube/mastic) control — using a high-permittivity semiconducting or capacitive-graded material sleeve that redistributes the field axially along a longer path instead of concentrating it at a point.

Heat-shrink, cold-shrink, and push-on terminations all deliver one of these two stress-control mechanisms, just through different installation methods and material systems.

The Method: Electrical Stress Formula and Sizing Logic

The starting point for any termination engineering check is the electric field at the screen cut-back edge, approximated using the coaxial cylindrical capacitor stress formula:

E = V / [r × ln(R/r)]

Where: – E = electric field stress at the inner radius (kV/mm) – V = phase-to-ground voltage applied across the insulation (kV) – r = radius of the conductor/screen cut-back point (mm) – R = outer radius of the insulation (mm) – ln = natural logarithm

Without stress control, the field at the screen edge approaches a near-singular concentration because the effective “r” at that sharp edge becomes very small, driving E toward very high values. A stress cone or stress-control tube effectively increases the local radius of curvature and/or the effective dielectric path length, which — because E is inversely proportional to r and to ln(R/r) — directly reduces the peak gradient to a manageable level.

The selection logic for a termination therefore follows three sizing checks:

1. Voltage class match — the termination’s rated voltage and rated lightning-impulse withstand must meet or exceed the cable system’s rated voltage class and insulation level.
2. Conductor size range — every termination kit covers a specific cable conductor cross-section and insulation diameter window; installing outside that window compromises the stress-control geometry.
3. Creepage distance for environment — outdoor terminations in polluted, coastal, or desert-dust environments need longer creepage paths (achieved via sheds/skirts) than indoor terminations in a clean switchgear cubicle.

Worked Example: Stress Reduction With a Stress Cone

Consider an 11 kV system (phase-to-ground voltage ≈ 6.35 kV, since V_phase = V_line/√3 = 11/1.732 ≈ 6.35 kV) terminating a cable with a conductor-plus-insulation screen cut-back radius of r = 10 mm and an outer insulation radius at the stress-control point of R = 14 mm.

Step 1 — Stress without any control (approximated at the sharp screen edge): If the effective radius at the sharp cut edge is very small — say r_edge ≈ 1 mm — the stress approximates to:

E_uncontrolled ≈ V / [r_edge × ln(R/r_edge)] = 6.35 / [1 × ln(14/1)] = 6.35 / ln(14) = 6.35 / 2.64 ≈ 2.4 kV/mm

Step 2 — Stress with a stress cone applied (effective radius increased to r = 10 mm, R = 14 mm):

E_controlled = V / [r × ln(R/r)] = 6.35 / [10 × ln(14/10)] = 6.35 / [10 × 0.336] = 6.35 / 3.36 ≈ 1.89 kV/mm

Step 3 — Compare: Even this simplified calculation shows the stress-cone geometry pulling the peak field down toward the bulk cable insulation stress level, rather than the sharp, highly localized multiplication that occurs at an unprotected screen cut edge. In practice, the uncontrolled edge stress is far more concentrated than this illustrative flat comparison suggests (real field solutions use finite-element analysis), but the first-principles direction is clear: increasing the effective radius and dielectric path length at the screen termination point is what a stress cone, a heat-shrink stress tube, or a cold-shrink body is engineered to achieve.

This is why every reputable termination kit datasheet specifies an exact cable conductor and insulation diameter range — the stress-control component is only effective within its designed geometric window.

Comparison Table: Heat-Shrink vs Cold-Shrink vs Push-On

Selection Criteria and Common Pitfalls

1. Match the voltage class and BIL, not just the cable voltage rating. A termination must be rated for the system’s lightning-impulse withstand level and continuous voltage, not just the nominal cable voltage printed on the drum.

2. Verify the conductor and insulation diameter window. Every stress-control component (cone, tube, or molded body) is only effective within its designed diameter range — installing a kit outside its window is a leading cause of premature termination failure, regardless of which of the three technologies is chosen.

3. Account for indoor vs outdoor creepage requirements. Outdoor terminations exposed to pollution, salt fog, or desert dust need additional creepage distance via sheds; indoor terminations inside a clean, dry switchgear cubicle typically need less.

4. Consider site conditions and hot-work restrictions. Cold-shrink and push-on technologies avoid open-flame or hot-air installation, which matters in hazardous-area work, confined cable vaults, or sites where hot-work permits are difficult to obtain. Heat-shrink remains popular where its wide dimensional tolerance and lower kit cost outweigh the need for a controlled heating tool and trained installer.

5. Don’t ignore screen bonding and grounding. Whichever termination technology is used, the cable’s metallic screen must still be correctly bonded and grounded per the cable’s screen-bonding scheme (single-point, both-ends, or cross-bonded) — the termination kit does not substitute for correct screen earthing design.

6. Confirm compatibility with the switchgear’s cable box or bushing. Terminations ultimately connect into switchgear cable compartments, transformer bushings, or ring main unit cable chambers — refer to the governing MV switchgear and transformer technical guides to verify clearance, IP rating, and interface compatibility before specifying a termination kit.

7. Protection coordination is a separate, downstream check. A correctly stress-controlled termination reduces the risk of a fault originating at the cable end, but overall system protection — fed by MV protection relays — must still be coordinated to clear any downstream fault quickly and selectively.

Standards and Compliance

Medium-voltage cable accessories, including heat-shrink, cold-shrink, and push-on terminations, are governed internationally primarily under the IEC 60502 series for power cables with extruded insulation and their accessories, and under IEC 60840 / IEC 62067 for higher-voltage extruded cable systems where applicable to the voltage class. Cable termination and joint test methods and type-test requirements are also commonly referenced against CENELEC HD 629 and relevant national adoptions in different export markets. Projects in the Middle East, North Africa, CIS, and Sub-Saharan Africa frequently specify compliance to the IEC series above alongside local utility or EPC-specific accessory qualification tests — always confirm the governing standard and test certificate with the manufacturer’s type-test report rather than assuming blanket conformity.

Related guides

See also our guides on medium voltage switchgear, gas-insulated switchgear and metal-clad switchgear.