Creepage Extension Sheds (CES)
Creepage extension sheds designed to increase creepage distance and improve insulation performance at outdoor medium-voltage cable terminations — providing reliable tracking and pollution resistance in coastal, industrial, and environmentally stressed installations up to 33 kV.
Extending Creepage Distance at Outdoor MV Terminations
Creepage extension sheds are moulded polymeric components applied over outdoor medium-voltage cable terminations to increase the surface creepage distance between the live conductor and earthed metalwork. In polluted environments, surface contamination combined with moisture creates leakage current paths along the termination surface — a shorter creepage distance accelerates tracking and flashover risk. CES extend this distance by adding profiled shed geometry over the termination body, forcing current to travel a longer surface path.
The sheds are applied to standard heat shrink or polymeric MV terminations as a retrofit or at initial installation — allowing the termination system to meet the creepage requirements of IEC 60815 pollution severity classes without replacing the core termination assembly. Each shed unit adds an incremental creepage contribution; the number of sheds per termination is determined by the system voltage and the pollution severity classification of the installation site.
- Material High-grade polymeric insulation
- Voltage MV up to 33 kV
- Colour Red (standard)
- Tracking resistance IEC 60587
- Pollution standard IEC 60815
- UV rated Yes
- Installation Slip-over — no heat required
Why Creepage Extension Sheds Are Specified
Engineered for outdoor MV environments where standard termination creepage distances are insufficient for the pollution severity of the site.
Increased Creepage Distance
Each shed unit adds a defined incremental creepage contribution to the termination assembly — allowing the total creepage distance to be brought into compliance with IEC 60815 requirements for the pollution severity class of the installation site.
Tracking and Flashover Resistance
Anti-tracking compound formulation resists the formation of carbonised surface paths under combined electrical stress and pollution loading — directly addressing the primary failure mechanism at outdoor MV terminations in contaminated environments.
Pollution and Moisture Resistance
Shed profile geometry causes water sheeting and contaminant runoff — preventing the formation of a continuous conducting moisture film across the termination surface. The material is resistant to salt deposits, industrial pollutants, and biological contamination.
UV and Weather Resistance
UV-stabilised compound maintains material integrity and shed profile geometry through prolonged direct outdoor exposure — including high UV index tropical and coastal environments where surface degradation of standard polymers is accelerated.
Retrofit and New-Build Suitability
Slip-over installation — no heat application required — allows CES to be applied to existing terminations in service as a retrofit upgrade when pollution severity conditions change, or installed during initial termination assembly on new-build projects.
No Specialist Tools Required
Installation requires no heat equipment, resins, or mechanical fasteners — the shed slips over the termination body and is positioned by hand. Minimal installation time at the termination with no modification to the core termination assembly.
Material & Performance Data
Reference data for engineering and procurement. Contact our technical team for creepage calculation support or IEC 60815 site classification guidance for your installation.
| Base material | High-grade anti-tracking polymeric insulation — UV-stabilised, outdoor rated |
|---|---|
| Colour | Red (standard) |
| Voltage application | Medium voltage — up to 33 kV system voltage |
| Tracking resistance | Anti-tracking grade — compliant with IEC 60587 |
| Pollution classification | Designed for use in IEC 60815 pollution severity classes II, III, and IV (medium to very heavy) |
| UV resistance | Yes — UV-stabilised, rated for continuous direct outdoor exposure |
| Installation method | Slip-over — no heat, adhesive, or mechanical fasteners required |
| Operating temperature | –55°C to +90°C (continuous service) |
| Compatible termination types | Heat shrink MV terminations, polymeric outdoor termination systems |
| Applicable standards | IEC 60587 (tracking and erosion resistance), IEC 60815 (pollution severity classification) |
Where Creepage Extension Sheds Are Used
Specified wherever outdoor MV termination creepage distances are insufficient for the pollution severity classification of the site.
Outdoor MV Cable Terminations
Primary application — applied over 11 kV and 33 kV outdoor cable terminations at substation cable entries, overhead line transitions, and pole-top terminations to increase creepage distance at the termination body.
Coastal and Marine Environments
Coastal installations where salt-laden air deposits conductive contamination on termination surfaces — a high-pollution severity condition requiring extended creepage distances to maintain insulation integrity in service.
Industrial and Polluted Sites
Industrial facilities where airborne pollution from manufacturing processes, chemical plants, or heavy transport creates elevated surface contamination levels at outdoor MV equipment and cable termination points.
Distribution Substations
Outdoor substation cable entries and transformer terminations in utility distribution networks — where IEC 60815 site pollution classification requires creepage distances beyond those provided by standard heat shrink termination assemblies.
Overhead Line Transition Points
Underground-to-overhead cable transition terminations at pole and tower bases — exposed terminations in open environments subject to weather, pollution accumulation, and UV degradation requiring extended creepage for reliable long-term performance.
Retrofit Upgrades on Existing Terminations
Applied to in-service terminations where pollution severity has increased since original installation — for example, following site expansion, changes in industrial activity, or reclassification of the site pollution level under IEC 60815.
How to Select the Right CES Configuration
Four parameters determine the correct shed size and quantity for your termination. Creepage calculations should be confirmed against IEC 60815 before finalising the shed specification.
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01
System Voltage
Confirm the system voltage of the cable termination where CES will be applied. The required creepage distance increases with voltage — the number of sheds required per termination is determined by the combination of system voltage and site pollution severity. CES are rated for MV applications up to 33 kV. For voltages above this range, contact our technical team for guidance.
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02
Required Creepage Distance
Determine the total creepage distance required for the termination using IEC 60815 — which defines creepage distance in mm/kV for each pollution severity class. Calculate the required total from the system voltage and the site pollution class, then subtract the creepage distance provided by the base termination assembly to find the additional creepage that must be contributed by the sheds. Divide by the per-shed creepage contribution to determine the number of sheds required. Contact our technical team for assistance with this calculation.
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03
Site Pollution Severity Class
Classify the installation site using IEC 60815 pollution severity classes — ranging from Class I (very light) to Class IV (very heavy). Typical classifications: coastal and marine environments = Class III or IV; industrial areas = Class III; rural areas = Class I or II. Site classification should be confirmed from the project specification or by assessment of the specific environmental conditions at the installation location. CES are designed for Class II, III, and IV environments.
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04
Termination Type and Bore Diameter
The shed internal bore must fit over the outer body of the termination to which it is applied. Measure the outer diameter of the termination body at the position where each shed will be seated — or provide the termination part number so compatibility can be confirmed. CES are available in a range of bore diameters to suit standard heat shrink and polymeric MV termination outer diameters. Confirm bore diameter before ordering to ensure the shed seats correctly without excessive play.
Creepage distance calculations should be confirmed against IEC 60815 before finalising the CES specification. Our technical team can assist with site pollution classification, creepage calculations, and shed quantity determination for your termination and voltage level.
Common Technical Questions
Creepage distance is the shortest path along the surface of an insulator between two conductive parts at different potentials — in the context of a cable termination, between the live conductor at the top of the termination and the earthed cable screen or metalwork at the base. In dry, clean conditions, even a short creepage path is adequate. In polluted or wet conditions, surface contamination creates a conducting film that allows leakage current to flow along the termination surface. If the creepage path is too short for the voltage and pollution level, this leakage current can generate heat, cause surface tracking, and ultimately result in flashover. Increasing creepage distance reduces the risk of this failure mode by forcing the surface leakage current to travel a longer, more resistive path.
The number of sheds is determined by the system voltage, the IEC 60815 pollution severity class of the installation site, and the creepage distance already provided by the base termination. The calculation is: total required creepage distance (from IEC 60815, in mm/kV × system phase-to-phase voltage in kV) minus the base termination creepage distance, divided by the per-shed creepage contribution. Contact our technical team with your system voltage and site pollution class — we can perform this calculation and confirm the shed quantity required for your specific termination assembly.
CES can be applied to existing terminations as a retrofit when the termination is de-energised. The slip-over installation method does not require removal or modification of the existing termination — the sheds are positioned over the termination body and seated in the correct locations. However, retrofitting to a live energised termination is not permitted — the cable circuit must be isolated and made safe before CES are installed or repositioned. For sites where pollution severity has increased after initial installation, CES provide a cost-effective upgrade without requiring full termination replacement.
IEC 60815 is the international standard for selecting and dimensioning high-voltage insulators for service in polluted conditions. It defines four pollution severity classes — Class I (very light) through Class IV (very heavy) — and specifies the required unified specific creepage distance in mm/kV for each class. To use IEC 60815 for CES selection: determine the site pollution class from the environmental conditions, multiply the required creepage distance factor (mm/kV) by the system phase-to-phase voltage to get the total required creepage in mm, then confirm whether the existing termination provides sufficient creepage or whether CES are required to make up the shortfall. Our technical team can assist with this process.
CES are compatible with heat shrink and polymeric MV outdoor terminations where the termination body outer diameter falls within the bore range of the available shed sizes. Compatibility with porcelain or glass disc insulators is not standard — CES are specifically designed for use with polymeric termination systems. To confirm compatibility with a specific termination, provide the termination type and the outer body diameter at the shed mounting positions when contacting our technical team.
CES are designed to seat on the termination body by interference fit or by resting against the termination profile without requiring adhesive. The shed geometry and bore sizing are selected to ensure the shed sits securely without migration under service conditions. For specific termination geometries where the shed bore diameter is at the upper end of the accommodation range, or where the termination is installed at a significant angle from vertical, contact our technical team to confirm whether additional retention measures are required for the specific installation.
Need Help Selecting the Right CES Configuration?
Speak with our technical team for creepage calculations, IEC 60815 site classification guidance, and termination compatibility confirmation.