Guide to 38/66kV High Voltage Cable Specifications, Construction, and Selection

A 38/66kV high voltage cable is designed for power networks where the specified system voltage and insulation coordination require a cable in this voltage class. Before selecting one, confirm the project’s voltage designation, applicable standard, installation conditions, conductor size, insulation system, and accessories. A common design uses a stranded copper or aluminum conductor, XLPE insulation, metallic screening, and a protective outer sheath, but the exact construction must match the network and route. At Zhongdong Cable, we recommend starting with the project specification and installation details rather than choosing a cable by voltage label alone.

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Key Takeaways

• Confirm the full voltage notation, including U₀, U, and U_m, against the relevant grid requirements.
• Choose conductor material and cross-section through load, fault-current, voltage-drop, and installation calculations.
• Specify insulation, screens, armour, sheath, and accessories to suit the electrical, mechanical, and environmental conditions.
• Request documentation that identifies the governing standard, test requirements, construction, and delivery scope.

Who This Guide Is For

This guide is intended for utility engineers, EPC contractors, project procurement teams, and distributors sourcing 38/66kV cable for transmission or distribution infrastructure. It is useful during early specification development as well as when comparing supplier quotations. It is not a substitute for network studies, local regulations, or approval by the project’s responsible electrical engineer.

What Does 38/66kV Mean?

Voltage notation identifies the cable’s relationship to the system voltage and insulation design. In IEC-style notation, U₀ is the rated power-frequency voltage between conductor and earth, U is the rated voltage between conductors, and U_m is the highest system voltage for which the equipment is designed. The project may use a regional designation such as 38/66kV, so buyers should not assume that the label alone defines every insulation or test requirement.

Confirm the complete designation and applicable cable standard in the tender documents. For high-voltage extruded-insulation cables, IEC 60840 is commonly referenced for systems above 30kV up to 150kV, subject to its scope and the project’s adopted edition. The specification should also state any national requirements, utility rules, and acceptance criteria.

Construction and Material Options

Conductor

The conductor is typically stranded copper or aluminum. Copper offers higher conductivity for a given cross-section, while aluminum may be selected when weight, material cost, or project design favors it; the choice should be based on calculated performance and total installed cost. Conductor cross-section depends on continuous load, short-circuit duty, route length, installation method, and allowable voltage drop.

Conductor Screen, Insulation, and Insulation Screen

Extruded semiconductive screens are commonly used around the conductor and insulation to support a smooth electric-field distribution. XLPE is a widely used insulation material for high-voltage cables, but its suitability and design must be confirmed against the required standard and operating conditions. For XLPE designs, 90°C is a commonly specified maximum continuous conductor temperature; the project specification and cable construction determine the applicable limit.

Metallic Screen, Armour, and Outer Sheath

A metallic screen provides an electrical path for charging and fault currents and may be made from wires, tape, or another specified arrangement. Its cross-section and bonding method should be checked against earth-fault current, protection-clearing time, and induced-voltage requirements. Depending on the route, the cable may also include armour or other mechanical protection, plus an outer sheath selected for the installation environment.

Direct burial, duct installation, tunnels, substations, and exposed sections can impose different mechanical, moisture, chemical, and fire-performance requirements. The specification should define any water-blocking measures, sheath material, armour type, and special protection needed. Avoid adding construction layers by default: each should address a documented project condition.

Key Specifications to Confirm

For XLPE-insulated designs, a short-circuit conductor temperature limit of 250°C is often used as a reference value, typically for a limited fault duration such as 5 seconds. This is not a universal guarantee: the actual permissible temperature and duration depend on the design, standard, and calculation assumptions. Ask the supplier to state the values and method used for the offered cable.

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How to Select a 38/66kV Cable

1. Confirm the Network and Standard

Record the nominal system voltage, highest system voltage, earthing arrangement, frequency, and expected operating conditions. Identify the governing IEC or national standard and the utility’s additional requirements. If the project documentation uses a voltage notation that differs from supplier catalogues, request a written confirmation of equivalence rather than relying on a similar product name.

2. Provide the Route and Load Data

Share the expected load, conductor material preference, route length, installation method, ambient or soil conditions, grouping, and any relevant thermal-resistivity data. These details affect current-carrying capacity and can change the conductor size required. The final selection should be supported by the project’s electrical and thermal calculations.

3. Check Fault Duty and Screen Design

Provide the prospective earth-fault current and protection-clearing time so the metallic screen can be reviewed for the specified duty. Confirm the cable bonding arrangement, because bonding choices affect induced voltages and circulating currents. Treat conductor sizing and screen sizing as related but separate engineering checks.

4. Match Construction to the Installation

Describe whether the cable will be buried, installed in ducts, laid in a tunnel, or routed through other environments. Specify pulling tension, minimum bending radius, route constraints, exposure to moisture or chemicals, and mechanical protection where these are known. This allows suppliers to quote a suitable construction instead of making assumptions that may affect installation or service.

5. Review Accessories and Delivery Scope

Joints and terminations must match the cable’s voltage class, conductor, insulation dimensions, screen arrangement, and installation environment. Confirm whether accessories, installation support, test documentation, drum details, and any required inspection are included in the quotation. Cable and accessory compatibility should be resolved before procurement is finalized.

Price, MOQ, and Lead Time

Pricing for 38/66kV cable depends on factors such as conductor material and size, insulation design, metallic screen, armour, sheath, order length, accessories, and applicable testing or inspection requirements. Minimum order quantities and manufacturing lead times are supplier- and project-specific, so they should be confirmed in a formal quotation rather than assumed from general market information. For a useful comparison, issue the same technical schedule, delivery destination, quantity, and documentation requirements to each bidder.

Supplier Evaluation Checklist

• Does the quotation state the complete voltage designation and governing standard?
• Are conductor, insulation, screens, armour, and sheath described clearly?
• Does the supplier identify applicable routine, sample, and type-test requirements and their scope?
• Are technical deviations, assumptions, and exclusions listed in writing?
• Are drum lengths, packing, shipping terms, delivery schedule, and documentation defined?
• Can the supplier review the project data and respond to questions about cable construction and accessories?

At Zhongdong Cable, we can review your cable schedule and project conditions to help clarify the required construction and quotation scope. To begin, send the voltage designation, applicable standard, conductor requirements, route or installation method, order quantity, destination, and accessory needs. We can then assess the requested configuration and identify any details that need confirmation before a commercial offer is prepared.

Conclusion

Selecting a 38/66kV high voltage cable requires more than matching a voltage label: the cable’s rating, conductor, insulation system, screens, protection, accessories, and tests must fit the network and installation. Begin with the project standard and electrical design data, then check fault duty, route conditions, and supplier documentation. The practical next step is to share a complete technical schedule with prospective suppliers and resolve assumptions in writing before placing an order.

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