Dec 11, 2025

UNE HD 620 S3 Standard Explained: Structure, Testing Requirements, and MV Cable Compliance

Medium voltage cables rarely get much attention, yet anyone who has worked around substations, buried feeders, or wind farm trenches knows how quickly a quiet afternoon can turn noisy when an MV line fails. The UNE HD 620 S3 standard was created partly to avoid those situations. It describes how MV cables should be built and what they must endure before ending up underground or inside a duct or overhead for the next couple of decades. Manufacturers like TDDL cable also reference this framework when designing MV products for long-term field reliability.
UNE HD 620 S3 covers many specifications, the following is an introduction to RH5Z1: what it covers, why certain rules exist, and how the testing process usually plays out in real projects.

1. What Is RH5Z1Cable (UNE HD 620 S3)

UNE HD 620 S3 is applicable to Europe and the Americas. This standard covers a wide range of medium-voltage cable structures, including structural dimensions, electrical performance, mechanical performance, and installation methods. Due to the large number of product structures, this example will primarily focus on the RH5Z1.
RH5Z1 comes in four structures.

Type 10E-6: Single-core polyolefin sheathed cable, no flame retardant requirements.
Type 10E-7: Single-core polyolefin sheathed cable, minimum CPR rating Eca.
Type 10E-8: Single-core polyolefin sheathed cable, minimum CPR rating Cca-s1b,d2,a1。
Type 10E-9：Multi-core polyolefin sheathed cables with steel carrier are used in overhead and power distribution systems.

2. Required Cable Structure

The basic structure of the RH5Z1 product is as follows:

2.1 Conductors

Aluminum or copper. Class 2 compacted round, dominates for cost and weight reasons. Aluminum is the most common conductor material, while copper conductors are less common. The appropriate specification should be selected based on factors such as current carrying capacity and installation conditions. The conductor must meet strict resistance and dimensional tolerances. If water resistance is required, TDDL cable chooses to use semi-conductivity water-blocking tape to meet the requirements.

2.2 Insulation

Conductor screen and XLPE insulation and insulation screen are produced using a CCV production line and extruded in a single process, maintaining excellent electrical performance.

2.3 Water blocking tape

If water resistance is required, TDDL cable chooses to use semi-conductivity water-blocking tape to meet the requirements.

2.4 Metallic Screening

The material uses longitudinally wrapped aluminum-plastic composite tape with a nominal thickness of 0.3mm and an overlap width of not less than 5mm. It meets the requirements for shielding grounding protection and radial water resistance. The metal shield must be bonded to the sheath.

2.5 Outer Sheath

The polyolefin sheath is UV resistant, abrasion resistant, low smoke, and halogen-free.

1 Conductor 2 Conductor screen 3 Insulation 4 Insulation screen
5 Water blocking tape 6 Metallic Screening 7 Outer Sheath

2.6 Additional Oxygen Barrier

To improve the fire resistance (CPR rating) of the cable, an oxygen barrier layer of a different color from the outer sheath can be extruded.

2.7 Steel Strand

Suitable for overhead systems, using 50mm² steel strand as the load-bearing conductor. The conductor's tensile strength meets requirements. Extruded 1.2mm thick black XLPE insulation provides weather resistance and protection.

3. Electrical and Mechanical Performance Requirements

These performance expectations directly influence how long an MV circuit stays healthy.

3.1 Electrical Performance

Cables must demonstrate strong insulation resistance, low dielectric loss, good thermal stability under normal load, and controlled partial discharge levels. These aren’t just numbers on a data sheet. Good electrical performance is essential to ensure the product's performance and lifespan.

3.2 Mechanical Performance

The mechanical properties, high and low temperature performance, and aging resistance of RH5Z1 cables should meet the standard requirements. The standard provides detailed specifications for the traction force, bending radius, temperature, and fixing involved in installation, storage, and transportation.

4. Environmental and Fire Requirements

MV cables operate in tough places: wet tunnels, dusty factories, underground ducts with standing water. The standard requires resistance to moisture, UV exposure (for outdoor cases), and temperature changes. Fire behavior also matters. Flame spread, smoke levels, and burning characteristics must meet defined thresholds, especially when cables run through public infrastructure. The CPR rating of the cable shall comply with standard EN 50575.

5. Where These Cables Are Used

Suitable for overhead or buried lines in power distribution systems.

5.1 Distribution Networks

Urban feeders, rural take-offs, and substation links rely on stable MV circuits. Failures here aren’t just technical issues; they often become urgent maintenance missions in the middle of the night.

5.2 Renewable Energy

Wind and solar farms bury MV collectors that aren’t touched again for twenty years unless something goes wrong. Stable insulation, predictable thermal performance, and low partial discharge behavior are essential.

5.3 Infrastructure and Industry

Rail tunnels, wastewater facilities, airports, and heavy industrial plants all use standardized MV cables because unplanned outages are expensive and disruptive. A harmonized standard keeps procurement and approvals straightforward.

6. How Compliance Works

Manufacturers must go through a mix of type tests, routine tests, and sample tests, and companies like TDDL cable typically keep long-term records to monitor whether materials or processes changes over the years.

6.1 Type Tests

These are carried out once for each design. They include dielectric tests, heating cycles, partial discharge checks, impact and pressure tests, aging simulations, water penetration tests, and flame tests. A failed type test often means adjusting materials or design.

6.2 Routine Tests

Performed on every production length. They cover conductor resistance, insulation thickness, sheath spark tests, and dimensional checks. Routine tests catch gradual drift in production before it becomes a field issue.

6.3 Sample Tests

Periodic checks—tensile strength, elongation, thermal aging—help confirm that materials stay consistent. These results often end up in quality logs that engineers revisit when something unusual is reported from the field.

7. Why This Standard Matters

UNE HD 620 S3 gives utilities, EPCs, and installers a shared technical baseline. Everyone involved can predict how the cable will behave, which reduces surprises during installation and operation. For long-term reliability, sticking to a known standard simply avoids trouble later, especially across networks that stretch over wide and mixed environments.

FAQ

Q: What voltage levels does UNE HD 620 S3 apply to?

A: Usually 3.6/6, 6/10, 8.7/15, 12/20, and 18/30 kV.

Q: Is UNE HD 620 S3 identical to IEC 60502-2?

A: They have many similarities, but UNE HD 620 S3 is mainly used in Europe and America and provides more detailed descriptions of the structure, materials, electrical and non-electrical properties, installation, storage and transportation of different cables.

Q: Does RH5Z1（UNE HD 620 S3）define cable model names?

A: Yes. It sets performance and construction rules.

Q: Where are these cables of RH5Z1(UNE HD 620 S3 ) usually installed?

A: Distribution networks, renewable plants, industrial facilities, and major infrastructure systems.

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