IEC Standard XLPE Insulated Low-Smoke Zero-Halogen Flame Retardant Medium Voltage Power Cable

Design and Compliance Basis
This product is designed, manufactured, and tested in strict accordance with the IEC (International Electrotechnical Commission) system of standards, ensuring that all performance aspects meet advanced international levels.

Core Standards
- IEC 60502-2:2014+AMD1:2024 CSV: "Power cables with extruded insulation and their accessories for rated voltages from 1 kV up to 30 kV – Part 2: Cables for rated voltages from 6 kV up to 30 kV". This is the core standard specifying cable construction, dimensions, and test requirements, applicable to fixed-installed extruded solid dielectric power cables for voltages from 6 kV up to 30 kV.
- IEC 60228: "Conductors of insulated cables". Specifies DC resistance requirements for conductors.
- IEC 60754-1/-2: "Test on gases evolved during combustion of materials from cables – Determination of halogen acid gas content and acidity". Specifies halogen-free performance requirements.
- IEC 61034-1/-2: "Measurement of smoke density of cables burning under defined conditions". Specifies low-smoke performance requirements.
- IEC 60332-1-2 / IEC 60332-3: "Tests on electric and optical fibre cables under fire conditions". Specifies flame retardant performance requirements (vertical flame test on a single cable and vertical flame test on bunched cables).

IEC 60502-2:2014, the third edition, replaced the 2005 second edition. Key technical revisions include simplification of the calculation procedures for lead sheath and oversheath thicknesses, addition of a method for determining conductor temperature, modification of the routine voltage test procedure, addition of an electrical test on the oversheath, and modification of requirements for non-metallic sheaths (including semi-conductive layers). The amendment published in 2024 (AMD1:2024) further supplements the latest technical requirements.

Special note: This standard applies to fixed installations such as distribution networks or industrial facilities, but does not apply to special installation and service conditions such as overhead lines, the mining industry, nuclear power plants (containment area and its vicinity), submarine or shipboard applications.

Cable Construction and Materials
The low-smoke zero-halogen flame retardant medium voltage power cable adopts a triple-layer co-extrusion process of conductor screen + XLPE insulation + insulation screen, effectively eliminating air gaps and ensuring very low partial discharge. The typical product construction is as follows:

Typical Construction Layers
1. Conductor: Annealed stranded copper (single-core or multi-core), complying with IEC 60228 Class 2 stranded conductor requirements. Function: Electrical energy transmission.
2. Conductor screen: Extruded semi-conductive compound. Function: Uniforms the electric field distribution and prevents air gaps between conductor and insulation.
3. Insulation layer: Cross-linked polyethylene (XLPE). Function: Core electrical insulation layer.
4. Insulation screen: Extruded semi-conductive compound. Function: Uniforms the electric field distribution outside the insulation.
5. Metallic screen: Copper tape or copper wire wrapping. Function: Carries fault current and shields against electromagnetic interference.
6. Filling and binding: Polypropylene fillers and non-woven fabric tape. Function: Maintains cable roundness and provides cushioning protection.
7. Inner covering (bedding): Polyolefin (PVC or PE optional). Function: Isolates the armour layer from mechanically rubbing against the insulation screen.
8. Armour layer: Steel tape armour (double steel tape wrapping) or steel wire armour. Function: Enhances mechanical protection, withstands radial pressure and axial tension.
9. Outer sheath: Halogen-free low-smoke flame retardant polyolefin (LSZH). Function: Fire safety, environmental protection, mechanical protection.

The core insulation material XLPE possesses very high dielectric strength and thermo-mechanical properties. The outer sheath is a low-smoke zero-halogen flame retardant polyolefin material, halogen-free, with low smoke density during combustion and no release of toxic corrosive gases such as HCl.

Main Technical Parameters
4.1 Rated Voltage Grades
The product's standard rated voltage grades cover the following ranges:
- 3.6/6 (7.2) kV
- 6/6 (7.2) kV
- 6/10 (12) kV
- 8.7/10 (12) kV
- 8.7/15 (17.5) kV
- 12/20 (24) kV
- 18/20 (24) kV
- 18/30 (36) kV
- 21/35 (40.5) kV
- 26/35 (40.5) kV
These are the most common types and conductor cross-section coverage. Users can select based on the rated voltage of the power supply system in accordance with national standards such as the GB/T 12706 series. The maximum operating voltage can reach 1.2 to 1.5 times the rated voltage.

4.2 Operating Temperature
- Maximum continuous permissible operating temperature: 90 °C
- Maximum conductor temperature during short circuit (max. 5 s): 250 °C
- Minimum ambient operating temperature: -20 °C; installation temperature should not be lower than 0 °C

XLPE insulation raises the normal operating temperature from 70 °C for standard PVC insulation to 90 °C, while increasing the short-circuit withstand temperature from 160 °C to 250 °C, significantly enhancing the cable's current-carrying capacity and system reliability.

4.3 Bending Radius (per IEC 60502-2 / GB/T 12706)
- Single-core armoured cable: ≥ 15 × cable overall diameter (D)
- Multi-core armoured cable: ≥ 12 × cable overall diameter (D)

4.4 Key Electrical Performance
- DC conductor resistance at 20 °C: Meets IEC 60228 requirements.
- Power-frequency voltage test: 2.5 kV / 5 min, no breakdown.
- Partial discharge test: At 1.73 U₀, no discharge exceeding the declared sensitivity is detectable.
- 4-hour power-frequency voltage withstand: 3.5 U₀ / 5 min, insulation no breakdown.

4.5 Mechanical Properties
Insulation:
- Tensile strength before ageing: ≥ 12.5 N/mm². After ageing (110 ± 2 °C / 240 h): variation ≤ ±30%.
- Elongation at break before ageing: ≥ 200%.
Sheath:
- Tensile strength before ageing: ≥ 12.5 N/mm². After ageing: ≥ 10.0 N/mm².
- Elongation at break before ageing: ≥ 300%. After ageing: variation ≤ ±30%.
Heat shrinkage test (80 ± 2 °C / 5 heating cycles): Sheath shrinkage rate < 3%.

Low-Smoke Zero-Halogen Flame Retardant Properties (Core Features)
These properties distinguish this product from standard XLPE cables and represent its core value in providing fire safety assurance for densely populated locations.

5.1 Flame Retardant Performance (IEC 60332 series)
Bunched cable flame test (IEC 60332-3): The charring extent on the sample does not exceed 2.5 m above the bottom edge of the burner.
Flame retardant performance is classified into different classes such as Class A, Class B, and Class C. Users can select the appropriate class of flame retardant products based on installation density and environmental requirements. Low-smoke zero-halogen flame retardant cables can also be supplemented with additional properties such as oil resistance, UV resistance, anti-termite, and anti-rodent.

5.2 Low-Smoke Performance (IEC 61034)
Smoke density measurement during cable combustion (light transmittance): Minimum light transmittance ≥ 60%. Some high-end products (e.g., super Class A flame retardant) can achieve ≥ 70%.
Sufficient light transmittance during a fire is essential for the safe evacuation of personnel. Traditional PVC cables produce a large amount of black smoke when burning, which can reduce visibility to less than 1 meter within minutes, seriously hindering escape.

5.3 Halogen-Free / Low Corrosivity Performance (IEC 60754)
- pH value (weighted): ≥ 4.3
- Conductivity (weighted): ≤ 10 μS/mm
- Individual halogen content (F, Cl, Br, I): ≤ 2 mg/g
- Total content of four halogens: ≤ 5 mg/g
Among the above indicators, a pH value ≥ 4.3 indicates that the combustion gas is not strongly acidic, conductivity ≤ 10 μS/mm indicates very low gas corrosivity, and total halogen ≤ 5 mg/g ensures that the sheath material does not contain halogens such as chlorine or bromine. Traditional PVC cables have a chlorine content of over 30%, and the HCl gas released during combustion corrodes equipment and severely damages the human respiratory tract.

5.4 Flame Retardant Performance Comparison
PVC Sheathed Ordinary Cable vs. This Product (XLPE + LSZH):
- Flame retardant class: None or low vs. Class A/B/C
- Combustion light transmittance: ≤ 20%, dense black smoke vs. ≥ 60%, good transmittance
- Combustion gas corrosivity: Strong acid (HCl), corrodes equipment vs. Weak acid/neutral, equipment safe
- Toxic gas release: Highly toxic dioxins, chlorine vs. Trace non-toxic gases
- Personnel safety: Severe threat vs. Safe evacuation assured

Product Model Designation
6.1 Common Domestic Model Examples
The domestic model designation for this product generally follows the following rules:
- Type prefix:
  - WDZ / WDZA / WDZB / WDZC — Halogen-free low-smoke flame retardant (Class A/B/C)
  - WDZN — Halogen-free low-smoke flame retardant and fire-resistant
  - NH — Fire-resistant
- Insulation code: YJ — Cross-linked polyethylene insulation (XLPE)
- Sheath code:
  - Y — Polyethylene sheath
  - E — Polyolefin sheath (low-smoke zero-halogen)
- Armour code:
  - 22 — Steel tape armour + PVC outer sheath
  - 23 — Steel tape armour + PE outer sheath
  - 32 / 33 — Steel wire armour (fine/coarse steel wire)

Example: WDZA-YJY23-8.7/15kV 3×240 mm²
Interpretation:
- WDZA: Halogen-free low-smoke flame retardant Class A
- YJ: XLPE insulation
- Y23: Polyethylene sheath + steel tape armour
- 8.7/15kV: Rated voltage
- 3×240 mm²: 3 cores × 240 mm² conductor cross-section

6.2 Common International Model Cross-References
A common corresponding model in the international market is N2XSEFGbY (IEC type), with the construction: copper conductor (Cu) / XLPE insulation / copper tape screen (CTS) / PVC inner covering / galvanized steel flat wire armour (SFWA) / PVC outer sheath, in accordance with IEC 60502-2. Customization based on samples is accepted, with low-smoke zero-halogen (LSHF/LSZH) outer sheath available as a premium option.

Application Areas
Due to its sound electrical performance and top-tier fire safety characteristics, this product is widely adopted in various high-safety-requirement projects:

7.1 Transportation Hubs and Public Facilities
- Subways and rail transit: Underground line installations must use low-smoke zero-halogen flame retardant cables to minimize harmful gases produced during cable combustion endangering personal health and evacuation during a fire. Above-ground lines should also preferably use low-smoke zero-halogen flame retardant cables.
- Airport terminals: High personnel density, high fire safety level.
- Railway tunnels, road tunnels.

7.2 Healthcare and Educational Institutions
- Hospitals: General hospital building codes require that power and control cables for emergency systems preferably be halogen-free low-smoke flame retardant type; clean surgery departments should preferably use low-smoke zero-halogen type.
- Schools, kindergartens.

7.3 Commercial and Industrial Facilities
- Super high-rise buildings, large shopping malls, hotels: Power cable design standards require that halogen-free insulated cables such as XLPE be used in densely populated places, and PVC insulated cables should not be selected.
- Underground substations, power plants.
- Data centers: Power distribution lines installed in concealed ventilation spaces should preferably use low-smoke zero-halogen flame retardant cables.
- Offshore platforms, chemical plants: XLPE insulation has outstanding resistance to chemical corrosion.
- Nuclear power plants, mines (note: IEC 60502-2 does not directly apply to nuclear power plant containment areas).

7.4 Key Considerations in Fire Protection Design
In densely populated places, the window for evacuation during a fire is very short. Traditional PVC sheathed cables release large amounts of dense black smoke (containing carbon black particles, with light transmittance generally below 20%) and highly toxic HCl (hydrogen chloride) gas during combustion, causing loss of visibility, respiratory tract damage, and asphyxiation within seconds. Low-smoke zero-halogen cables can raise light transmittance to 60% and above, while the combustion gases are weakly acidic/neutral, gaining valuable escape time for safe personnel evacuation. They also effectively protect fire emergency equipment such as alarms, smoke exhaust systems, and public address systems from malfunctioning due to corrosion.

Supplementary Notes
1. Flame retardant class classification: According to GB/T 19666-2019, flame retardant cables are divided into Class A, Class B, Class C, and Class D. Class A has the highest flame retardant performance and is suitable for main line installations in densely populated areas; Class D is only applicable to products with an outer diameter ≤ 12 mm or conductor cross-section ≤ 35 mm². This product typically achieves Class A or Class B flame retardancy.
2. International cooperation and adoption of standards: This product not only conforms to IEC standards but can also be manufactured according to different national or industry standards such as GB 12706, BS, DIN VDE, ASTM, flexibly meeting the demands of the global market.
3. Customization for special needs: Comprehensive customized solutions such as fire-resistant type (fire performance), oil-resistant type, UV-resistant type, anti-termite type, anti-rodent type, longitudinal water blocking type, A/B/C class flame retardant and low-smoke zero-halogen type can be provided according to specific project requirements.
4. Authoritative certifications: Products from well-known manufacturers have passed international authoritative certifications such as TÜV, CE, RoHS and third-party flame retardant test reports, ensuring the authenticity, reliability, and compliance of product performance.
5. Reference standards: The equivalent national adoption standards are GB/T 12706.2-2020 "Extruded insulation power cables and accessories for rated voltages from 1 kV (Um=1.2 kV) up to 35 kV (Um=40.5 kV) – Part 2: Cables for rated voltages from 6 kV (Um=7.2 kV) up to 30 kV (Um=36 kV)", and GB/T 19666-2019 "General rules for flame retardant and fire-resistant wires and cables or optical fibre cables".