Cable-Termination Geometry and Mechanical Loads in MV Switchgear

An MV cable termination is an electrical stress-control device attached to a mechanically active cable; it must not be used as the cable support. Bend force, cleat reaction, thermal movement and short-circuit thrust must be intercepted by the compartment structure so the lug, separable interface, screen cutback and switchgear bushing remain aligned and unloaded within declared limits.

This guide integrates cable/accessory standards with IEC 62271 assembly requirements. It covers lug and separable connectors, field control, bending geometry, phase arrangement, cleats, mechanical loads, screen bonding, testability and installation QA.

Executive conclusions

Freeze the exact cable, conductor, screen, accessory, connector/lug and switchgear interface as one qualified system.
IEC 60502-4:2023 tests accessories for cables to Um 36 kV; IEC 61442:2023 supplies test methods. The switchgear assembly/interface still requires IEC 62271 evidence.
IEC 61238-1-3:2018 applies to relevant compression/mechanical cable connectors—not automatically to the complete termination or switchgear busbar joint.
Use the cable manufacturer’s minimum bending radius by cable construction, temperature and installation/setting condition. A universal “12D” rule is unsafe.
Locate the first cleat/support so cable weight and restoring force do not load the termination, yet without creating an unachievable bend or blocking stress-control installation.
Obtain permissible axial, lateral, torsional and bending loads/moments for the offered bushing/interface; “self-supporting termination” is not enough.
Short-circuit force acts on cables and conductors; IEC 61914:2021 cleat declarations/tests must match cable formation, diameter, mounting surface, current and restraint spacing.
Control screen cutback, semiconductive interface, stress-control component, lug depth and connector seating; millimetres can determine PD performance.
Check phase-earth/phase-phase clearances over installation tolerance, cable movement and test-adapter geometry.
Design access for torque/compression, cleanliness, phase identification, testing and safe isolation without damaging barriers or IAC pressure paths.

1. Standards and interface boundaries

Reference	Relevant scope
IEC 60502-2:2014+AMD1:2024, COR1:2026	Extruded MV cable construction/tests from 6 kV to 30 kV (Um 36 kV)
IEC 60502-4:2023	Type-test requirements for cable accessories in that range
IEC 61442:2023	Type-test methods for accessories, including separable-connector provisions
IEC 61238-1-3:2018	Compression/mechanical connectors for power-cable conductors to Um 36 kV
IEC 61914:2021	Cable cleats/intermediate restraints and electromechanical resistance declarations/tests
IEC 62271-200:2021+AMD1:2024	MV metal-enclosed assembly, cable compartment, dielectric/thermal/short-time/IAC boundary
IEC 60137:2017	Separately supplied insulated bushings above 1 kV where applicable
IEEE 386-2025	Current North American separable insulated connector system standard for 15–35 kV classes

Do not mix IEC/CENELEC/IEEE interface dimensions by appearance. Specify the governing connector interface and obtain dimensional/interchangeability evidence from both equipment and accessory manufacturers.

2. Build the interface data sheet

system/rated voltage, insulation level and earthing;
cable standard, conductor material/class/shape/area and resistance;
insulation/screen/oversheath material and diameters over layers;
wire/tape screen cross-section and fault duty;
termination/separable connector make, type, interface and rating;
lug/connector barrel range, compression dies/bolts and palm dimensions;
bushing/pad interface, stud/bolt and permissible terminal loads;
number of cables per phase and phase formation;
entry direction, gland/plate, cleat type/spacing and bending radius;
screen bonding, earth lead and test link;
continuous/short-circuit current and operating temperature;
installation temperature, pulling side and available work envelope.

3. Cable construction controls geometry

single-core versus three-core;
circular, compacted, sector or Milliken conductor;
copper versus aluminium and solid/stranded class;
XLPE/EPR insulation and bonded/strippable semiconductive screen;
copper wire/tape screen, concentric neutral or sheath;
armour type and oversheath;
water-blocking layers and swelling tapes;
overall diameter, tolerances, stiffness and minimum installation temperature.

IEC 60228:2023 controls conductor sizes/resistance characteristics, but manufacturer dimensional data is still needed for accessory selection. “1 × 240 mm²” is not enough to select a termination or bend envelope.

4. Minimum bending radius is condition-specific

cable type/construction and overall diameter;
during pulling versus after final setting;
single bend versus reverse/S-bend;
installation temperature and cold-soak;
armour/sheath and screen design;
bending around a former versus unsupported hand bending;
accessory manufacturer straight-length requirement;
number of parallel cables and formation.

Obtain the cable/accessory datasheet values and draw the actual cable centerline with tolerance. Check the inside radius at the neutral axis defined by the manufacturer, not the compartment diagonal.

5. Straight length below the termination

The accessory usually needs a straight, stable cable section for screen cutback, stress-control installation and connector alignment. A bend beginning inside the accessory can ovalize insulation, move the stress cone or side-load the interface. Define:

minimum straight length from interface/termination reference;
allowed angular misalignment;
distance to first cleat/support;
installation tool/hand clearance;
space for phase crossing and screen earth lead;
future disconnect/retermination length;
test-adapter/removal stroke.

6. Mechanical load model

cable self-weight, including vertical drop;
bending restoring force from final set;
pulling residual/twist and phase transposition;
thermal expansion/contraction and conductor/sheath differential;
short-circuit lateral/axial force;
seismic displacement where applicable;
foundation/lineup settlement and gland-plate movement;
installation tool and accidental service loads;
multiple cables reacting unequally on one palm/bushing.

Calculate forces/moments at the bushing/termination reference through the actual cleat locations and cable stiffness. Compare with manufacturer declared limits in each direction and load combination. Do not use the lug bolt to pull a misaligned cable into place.

7. Cleat and support philosophy

first cleat carries weight/restoring load without intruding into accessory straight zone;
subsequent cleats maintain formation under peak fault force;
mounting rail/plate and fasteners are part of the declared cleat system;
cleat liner fits actual cable diameter and does not damage oversheath;
axial restraint is provided where cable thrust/vertical weight requires;
intermediate restraints match tested formation;
spacing calculation/test basis uses peak current and cable-center spacing;
bracket/enclosure transfers load to frame/foundation;
thermal movement is accommodated without terminal loading;
inspection/replacement remains possible.

IEC 61914 tests a declared cleat configuration, including mounting surface and optional liners. A cleat’s headline kA is meaningless without formation, current waveform/peak, cable diameter, spacing and test method.

8. Short-circuit force on cables

Electromagnetic force grows approximately with peak current squared and inversely with conductor spacing in simple parallel geometry. For trefoil/flat arrangements, use the accepted calculation/cleat-selection method and the actual phase currents/centers. Check:

maximum peak current from IEC 60909 or governing study;
three-phase versus phase-earth path;
flat/trefoil and same-phase parallel circuits;
first cleat/terminal span and end effects;
cable impact between phases/enclosure;
axial movement and connector pull-out;
cleat, rail, bolt, plate and enclosure reaction;
screen/earth lead movement;
post-fault accessory/PD/dielectric condition.

9. Conductor connector/lug selection

conductor material, class, shape and actual diameter;
connector range, barrel length and insertion stop;
compression die/index/sequence or shear-bolt procedure;
Al/Cu transition and contact compound;
palm hole/stud size, orientation and plating;
rated/short-time current and temperature cycling;
mechanical tensile class/load;
separable connector’s required contact pin/adaptor;
tool calibration, maintenance and operator qualification;
IEC 61238-1-3 report matching the conductor/connector combination.

10. Stress-control geometry

screen cutback dimension and edge quality;
semiconductor removal without insulation scoring;
insulation diameter and surface preparation;
stress cone/tube body position and orientation;
lubricant/cleaner compatibility and quantity;
void-free interface and final seating mark;
earth braid/screen continuity without sharp projections;
moisture sealing and oversheath transition;
phase identification not wrapped into high-field zone;
minimum phase/earth distances after complete assembly.

Do not “improve” the cutback or substitute consumables. IEC 60502-4 type approval is tied to accessory design/material/manufacturing; installation dimensions follow the exact kit/cable range.

11. Bolted palm/open-air termination

align palm faces without forcing cable;
control Cu/Al transition, plating and joint preparation;
use manufacturer bolt/washer/torque system;
keep cable/termination weight off the bushing stud;
verify lug rotation and closest bolt/edge clearance;
support outdoor-type termination skirts/stress cone as specified;
check thermal expansion and phase leads;
provide arc/barrier/compartment clearance and access.

12. Separable connector interface

interface profile/class and rated current/voltage;
deadbreak versus loadbreak functionality—never infer from shape;
bushing insert/contact pin/adaptor compatibility;
screened body earthing and touch-safe claim boundary;
required torque/operating tool and seating indicator;
parking stand, cap and spare-way earthing/insulation;
test-point function and compatible detector/cap;
mechanical support so cable torque does not rotate interface;
multi-cable elbows and stacking/adaptor load;
IEEE 386-2025 or applicable IEC/CENELEC evidence—do not mix regimes.

13. Screen bonding and earth path

single-point, both-end or cross-bonding design;
screen/sheath fault-current and induced-voltage calculation;
earth braid cross-section, length and short-time withstand;
low-impedance connection to the designated switchgear earth bar;
test link accessibility and safe isolation;
surge-voltage limiter where designed;
separation from high-field stress-control region;
no tight bend, sharp edge or unsupported fault movement;
armour bonding distinct from screen where applicable;
phase-consistent installation and labeling.

14. Thermal design

cable conductor ampacity for installed formation/ambient;
connector/lug contact resistance and current sharing;
bushing/pad/earthing contact heat;
enclosure ventilation and adjacent phase heating;
multiple cables per phase sharing tolerance;
screen/sheath circulating and eddy losses;
ferromagnetic gland/entry plate heating around single-core cables;
termination/accessory temperature limits;
IEC 62271 assembly temperature-rise evidence;
thermography/sensor access and baseline.

15. Cable entry and gland plate

non-magnetic layout/material for single-core AC cables as required;
avoid closed ferromagnetic loops around individual phases;
IP, fire/smoke, vermin and water sealing;
movement/cleat load transferred to structural frame;
edge protection and oversheath damage prevention;
spare openings sealed and field changes controlled;
earth/armour gland continuity where designed;
IAC pressure path/floor-plenum configuration preserved;
minimum bend radius from entry to first cleat/termination;
floor tolerance and trench interface.

16. Cable-test provisions

defined isolation from bus, VT and surge arrester;
approved test connection point/adaptor and voltage/duration;
termination/separable-connector test capability;
safe discharge and reinstatement of screen/earths;
remote cable-end control and communications;
barriers/clearances for test leads;
interlock/key/permit arrangement;
post-test removal of temporary links/adaptors/caps;
final phasing, insulation and connection checks.

17. Compartment layout review

Envelope	Review
Electrical	Phase/earth clearance, stress-control position, test adaptor and movement
Mechanical	Bend radius, straight length, cleats, terminal load and short-circuit motion
Thermal	Current sharing, joint heat, ventilation and gland eddy loss
Installation	Hands/tools/dies/torque/accessory stroke and phase sequence
Maintenance	Inspection, test, disconnection and spare cable length
Safety	Isolation/earth points, barriers, LSC and adjacent live parts
IAC/IP	Pressure relief, cable/floor sealing and door/cover condition

18. Installation QA hold points

verify cable drum/type/phase and kit compatibility;
inspect storage, moisture seals and installation temperature;
pull/position without exceeding force/radius/twist limits;
set final cleats/supports and relieve terminal load;
record cutback dimensions before covering;
inspect semiconductor removal and insulation surface;
verify connector insertion/compression/shear-bolt record;
install stress control/seal by qualified instruction;
align/seat/torque termination or separable connector;
bond screen/armour and record earth path;
check clearance, phase ID, test point/caps and compartment cleanliness;
perform specified electrical/PD/sheath/continuity tests;
photograph as-built geometry and close punch list.

19. Commissioning and condition baseline

lug/connector resistance or millivolt drop where specified;
screen/armour/earth continuity and bonding state;
phase identification/phasing;
insulation/accessory test per cable/project standard;
PD baseline where specified and method appropriate;
terminal mechanical load/cleat/support visual confirmation;
separable-interface seating/torque/earthing caps;
thermography under meaningful load;
photographic dimensions and as-built cable schedule;
manufacturer kit batch, installer and tool traceability.

20. Change triggers

cable manufacturer/construction/diameter/conductor class;
Cu/Al area or number of cables per phase;
termination/connector/interface/lug;
cutback, stress-control or consumable material;
entry direction/gland plate/cleat/spacing/rail;
bushing/pad/CT/VT or compartment dimensions;
fault level, screen bonding or clearing time;
ambient/loading/harmonics;
floor/trench/lineup movement;
IAC/IP sealing or test arrangement.

21. Common mistakes

using a universal bend-radius multiplier;
selecting accessory from conductor area alone;
pulling cable into alignment with terminal bolts;
letting the termination carry cable weight;
using a cleat kA claim without formation/spacing/mounting evidence;
mixing separable-interface standards;
incorrect screen cutback or scored insulation;
unprotected Cu-Al palm interface;
ferromagnetic closed gland loop around single-core phase;
screen earth lead too long/unsupported for fault duty;
blocking IAC pressure path with cables/seals;
changing cable/kit/cleat without type-test/application review.

Primary references

Safety note: Cable preparation, termination, testing and compartment access require qualified personnel under approved isolation, proving-dead, earthing and test procedures. Follow the exact cable/accessory/switchgear manufacturer instructions.