High-voltage insulated cable termination

01

Match the voltage class, impulse and withstand ratings

Elastimold's cable termination catalogue page (Thomas & Betts) gives an electrical ratings summary based on IEEE Standard 48 for its terminations on three-phase three- or four-wire systems and single-phase laterals. For the 15 kV class it lists 9.5 kV phase-to-ground, 110 kV BIL (1.2 × 50 µs wave), AC withstand of 50 kV for 1 minute dry, 35 kV for 6 hours dry and 45 kV for 10 seconds wet, and 13 kV corona extinction. [1]

The ratings quoted by makers refer to IEEE Std 48. Its 2009 edition (since superseded by 48-2020) covers all indoor and outdoor terminations on alternating-current shielded cables with laminated insulation from 2.5 kV to 765 kV or extruded insulation from 2.5 kV to 500 kV. Separable insulated connectors are excluded and covered by IEEE Std 386. It requires terminations and their component parts to withstand the tests it specifies. [3]

For the 25 kV class it lists 16 kV phase-to-ground, 150 kV BIL, AC withstand of 65 kV for 1 minute dry, 55 kV for 6 hours dry and 60 kV for 10 seconds wet, and 21.5 kV corona extinction. Its modular terminators for up to 35 kV use 4 modules at 15 kV, 8 at 25 kV and 10 at 35 kV. [1]

Editorial calculation: a 13.8 kV system has about 13.8 ÷ √3 ≈ 8.0 kV phase-to-ground, within the 15 kV class's 9.5 kV; a 22.9 kV system has about 13.2 kV, which needs the 25 kV class (16 kV). Check impulse levels against the system's insulation coordination, not only the phase-to-ground voltage.

Give the supplier the system voltage and earthing, BIL, indoor or outdoor service and pollution level, cable type (conductor material and size, insulation type and diameter, shield type), termination type (premoulded, modular, cold- or heat-shrink), connector and lug, mounting brackets, and test reports required.

02

Fit the cable and the service environment

The same catalogue describes its PCT1 and PCT2 single-piece terminators as providing sufficient creep, strike and weather sealing for Class 1 outdoor service, with an integral cable jacket seal. The 15 kV PCT1 fits cable insulation diameters of 0.640–1.070 in and the 25 kV PCT2 0.830–1.180 in; a positioning bracket fits overall cable diameters of 0.750–1.625 in. [1]

3M's Cold Shrink QT-III indoor tubular termination kits (7640-T and 7650-T series) show a different construction from Elastimold's premoulded and modular units. Each one-piece, non-skirted silicone rubber termination is pre-stretched on a removable core and shrinks into place when the core is unwound, with no force fit required. 3M states the kits conform to IEEE Std 48 Class 1 for 5, 8, 15, 25/28 and 35 kV terminations, for indoor and weather-protected use. They are designed for jacketed concentric-neutral and concentric-neutral solid-dielectric cables, with materials compatible with PE, XLPE and EPR insulation. Each kit makes one single-phase termination; lugs are not included. [2]

3M explains stress control as follows: High-K materials with a dielectric constant above 15 distribute the field beyond the cable shield cut-off. It gives stress in continuous shielded cable as about 50 V/mil next to the shield to about 70 V/mil at the conductor. It states that the termination keeps stress on the insulator surface below 15 V/mil at rated voltage. [2]

Its modular terminators are selected from tables by insulation diameter (from 0.775 in upward) and by conductor size and type, with threaded-rod or spade connectors and aluminium or universal contacts for aluminium or copper conductors. [1]

Editorial calculation: 0.640–1.070 in is about 16.3–27.2 mm and 0.830–1.180 in about 21.1–30.0 mm; measure the actual insulation diameter of your cable, not its nominal size, before choosing. [1]

03

Compare what suppliers offer

Suppliers linked to this page list cable termination kits; each card links to the page reviewed.

Listings include cable termination kits and straight joints supplied with low-, medium- and high-voltage power cables.

04

Check creepage, cable range and temperature limits on an outdoor kit

Ensto's product page for its COT1.2406 cold shrink outdoor termination kit shows how a kit rated by U0/U (Um) is specified: 12.7/22 (24) kV, for 1-core cables with Al/Cu conductors of 630–1000 mm², polymeric insulation and a Cu-wire screen, with components for three cable cores and termination bodies with integrated geometric stress control. It lists a creepage distance of 630 mm, a shed diameter of 116 mm, an installed length of 500 mm, a diameter on the insulation of 36.8–72 mm and an outer sheath of 47–72 mm; mechanical lugs for conductor and screen wire are not included. [4]

Its temperature limits are −25 to 50 °C for installation, −50 to 90 °C in operation and 5 to 40 °C in storage, and the page marks the kit as suitable for outdoor use and not for indoor use. [4]

Editorial calculation: 630 mm of creepage over a Um of 24 kV is about 26 mm/kV (630 ÷ 24 = 26.25), and 36.8–72 mm on the insulation is about 1.45–2.83 in (÷ 25.4), above the 0.830–1.180 in range of the 25 kV PCT2 above. Convert U0/U (Um) ratings and diameters before comparing kits from different markets. [4] [1]

05

Trace the termination components

This is a functional reference built from the sources cited; it is not one maker's specification.

06

Fill the specification fields with values for your cable

A termination quotation needs values for your cable and system. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

07

Send the system, cable and service data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

System: [voltage; earthing; BIL]
Service: [indoor or outdoor; pollution]
Cable: [conductor; insulation diameter; shield; jacket]
Termination: [type; connector; bracket]
Tests: [withstand; PD; impulse reports]
Quantity: [per size]

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