38/66kV High Voltage Cable Selection Guide: Specifications, Applications, and Sourcing

A 38/66kV high voltage cable is designed for power systems with a rated voltage of 38 kV between conductor and earth and 66 kV between conductors; the associated highest system voltage is commonly specified as 72.5 kV. Selecting the right cable requires more than matching this voltage designation: buyers also need to define conductor size and material, insulation and screen design, installation conditions, applicable standards, and project testing requirements. This guide explains how to prepare a practical specification, compare cable options, and evaluate suppliers before requesting a quotation.

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Who This Guide Is For

This guide is intended for utility and infrastructure project teams, EPC contractors, electrical consultants, distributors, and industrial buyers sourcing medium- and high-voltage power cable. It is also useful for procurement teams that have a voltage class but need to turn preliminary project information into a complete RFQ. Final cable selection should be confirmed by the project’s electrical designer against local regulations and the actual network conditions.

Understanding the 38/66kV Cable Rating

The notation 38/66 (72.5) kV describes three related voltage values: U₀ is 38 kV from conductor to earth, U is 66 kV between conductors, and U_m is a 72.5 kV system-voltage reference. These values are not interchangeable, so specifications should state the required voltage designation explicitly. A cable’s suitability also depends on how the network is earthed and the duration and frequency of earth faults.

Many designs in this voltage class use a stranded copper or aluminum conductor, a conductor screen, XLPE insulation, an insulation screen, metallic screening or sheathing, and an outer protective sheath. The exact construction varies with installation method, fault-current requirements, environmental exposure, and purchaser standards. Armor may be required for mechanical protection in some installations, but it is not a universal feature of every 38/66kV cable.

Types, Materials, and Key Specifications

Conductor and insulation choices

Copper and aluminum are common conductor options. Copper can allow a smaller conductor cross-section for a given electrical duty, while aluminum may be considered when project weight and material cost are important; the final comparison must include ampacity, joints, terminations, and lifecycle requirements. XLPE is widely used as insulation for extruded high-voltage cable, but the purchaser should specify the required design and compliance basis rather than relying on a material name alone.

Construction details to define

For a meaningful technical comparison, request a complete construction schedule rather than a short product description. It should identify conductor material and nominal cross-section, insulation thickness, conductor and insulation screen requirements, metallic screen or sheath arrangement, outer sheath material, and any armor or water-blocking features. Also define whether the cable is single-core or a specified alternative, and state the required drum lengths and marking information.

Match Cable Design to the Application

Typical application areas include utility substations, distribution and transmission connections, industrial power networks, and renewable-energy or infrastructure projects where the system design calls for this voltage class. The same nominal cable rating does not automatically make one construction suitable for every route. Direct burial, duct installation, cable trays, and outdoor terminations impose different thermal, mechanical, and environmental demands.

For underground routes, provide soil thermal conditions, burial depth, grouping, and duct details where available, because these can affect current-carrying capacity. For substation or industrial connections, clarify route length, short-circuit duty, earthing arrangement, and interfaces with switchgear and accessories. If the project includes joints or terminations, specify their voltage class and compatibility requirements along with the cable.

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A Practical Selection Framework

Step 1: Confirm the electrical duty

Start with the network voltage and the required cable rating, then document continuous load, overload expectations, short-circuit current, and fault-clearing time. The designer should calculate conductor size using the installation conditions and relevant design rules, not select a cross-section from voltage alone. Ask the engineering team to confirm that the cable, accessories, and system earthing assumptions are consistent.

Step 2: Define route and construction

Map the installation route and identify whether the cable will be buried, installed in ducts, exposed to sunlight, or subject to impact or chemical exposure. Use that information to set sheath, armor, water-blocking, and fire-performance requirements where applicable. Avoid adding construction features without a project need, as unnecessary complexity can affect cost and delivery.

Step 3: Specify standards, tests, and documentation

Name the governing standard and edition required by the project or jurisdiction, and ask the supplier to identify the exact product design offered against it. For 38/66kV extruded-insulation cables, IEC 60840 may be relevant depending on the project scope and applicable edition, but it should not be assumed to replace local requirements or purchaser specifications. List the required routine, sample, type, or prequalification evidence and clarify which records will accompany the shipment.

Step 4: Compare the complete offer

Review the technical schedule, deviations, unit price, drum length, packing, delivery terms, and payment conditions together. A low headline price is difficult to evaluate if the quote omits metallic screen details, accessories, inspection scope, or transport assumptions. Request a clear list of exclusions and confirm how any technical alternatives affect performance and commercial terms.

Pricing, MOQ, and Lead Time

Pricing for 38/66kV cable is typically influenced by conductor material and size, insulation and metallic components, order quantity, specified testing, drum configuration, and delivery destination. Minimum order quantities and production lead times vary by supplier and by the requested design, so they should be confirmed against the final bill of materials and delivery schedule. For budget planning, provide an estimated quantity and required delivery window early, then request a formal quotation after the technical scope is aligned.

Long cable routes may require multiple drums, so ask for the maximum practical drum length, shipping dimensions, and jointing implications. Confirm whether quoted lead time begins after technical approval, deposit, or another agreed milestone. These details help procurement compare offers on a like-for-like basis and reduce the risk of a cable arriving with unsuitable lengths or incomplete documentation.

Supplier Evaluation Checklist

• Can the supplier provide a construction drawing and complete technical data sheet for the offered voltage rating?
• Does the proposal identify the governing standard, edition, and any deviations?
• Are conductor, insulation, screen, sheath, and accessory details explicit?
• Can the supplier explain its quality-control and inspection documentation for the proposed order?
• Are production schedule, MOQ, drum lengths, packing, and delivery terms stated clearly?
• Is there a process for technical clarification and approval before production?

At Zhongdong Cable Co., Ltd., we encourage buyers to share their voltage designation, installation route, quantity, applicable standards, and target delivery schedule when requesting information. With these details, our team can review the requested scope and clarify the product and documentation requirements for a quotation. Buyers should evaluate the final offer against their approved project specification and request any required compliance or test evidence before placing an order.

Key Takeaways and Next Steps

Choose a 38/66kV high voltage cable by confirming the complete voltage designation, electrical duty, route conditions, construction, and project standards—not by voltage label alone. Define conductor and screen requirements, accessories, testing evidence, drum lengths, and delivery expectations in one RFQ so supplier offers can be compared fairly. The next step is to prepare a route and load summary, obtain engineering approval for the cable specification, and send the same technical package to shortlisted suppliers for review and quotation.

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