6491B H07Z-R Low Smoke Cable 450/750V BS7211

6491B cable is a single-core, stranded copper conductor cable insulated with Low Smoke Zero Halogen (LSZH) material. It is a harmonised type H07Z-R cable, meaning it’s rated at 450/750 V and uses a halogen-free thermosetting insulation. This cable is designed for fixed wiring installations where limiting smoke and toxic fumes in the event of fire is crucial. Commonly referred to as LSZH singles, 6491B cables are used inside conduit, trunking, and other protective enclosures for power and lighting circuits, switchgear, control gear, and building wiring. In practice, 6491B is the LSZH equivalent of the standard PVC-insulated single-core wire (6491X), offering enhanced fire safety for commercial and public installations.

Designation and Standards (6491B vs H07Z-R)

The designation “6491B” comes from British Standards and indicates a single-core non-sheathed cable with LSZH insulation. Its harmonised code “H07Z-R” breaks down as follows:

• H – Harmonised cable (built to an EU standard)
• 07 – Voltage rating of 450/750 V (U0/U)
• Z – Insulation material is zero-halogen, thermosetting (LSZH)
• R – Rigid stranded conductor (Class 2 stranding per IEC 60228)

In essence, H07Z-R is the European harmonised designation for 6491B cable. This cable is manufactured to BS EN 50525-3-41, the harmonised standard for halogen-free cross-linked insulation single-core cables (which replaced the older BS 7211 standard). It is typically BASEC approved, indicating it has been independently tested and certified for compliance.

Key fire performance standards are met by 6491B cables to ensure safety in fire conditions. They are flame-retardant per IEC 60332-1-2 and emit very low smoke (IEC 61034) with no halogen acid gases (IEC 60754) when exposed to fire. This means 6491B cables will not propagate fire easily, and if they do burn, they will not release dense smoke or corrosive fumes. These characteristics make them suitable for installations in public buildings where fire safety is paramount.

Construction and Materials

Conductor: 6491B cable uses a plain annealed copper conductor with Class 2 stranding (sometimes called “rigid stranded”). Class 2 stranded conductors provide some flexibility for installation while remaining relatively stiff, making them ideal for fixed wiring. Standard sizes range from small cross-sections like 1.5 mm² up to large 630 mm² conductors to cover a broad spectrum of electrical current requirements. The conductor complies with BS EN 60228 standards for copper conductivity and cross-sectional area.

Insulation: The insulation is a single layer of Low Smoke Zero Halogen compound, typically a thermosetting polymer (cross-linked polyolefin). In standards, this insulation type is classified as Type EI5 under BS EN 50363-5. Being thermosetting, it can operate at higher temperatures (90 °C) without melting or deforming. The insulation thickness varies by cable size, sufficient to meet the 450/750 V rating and electrical safety requirements.

Identification: 6491B cables are available in a variety of insulation colours to identify phases, neutrals, or earth conductors in wiring. Common colours include brown, black, grey, blue, red and white, orange or violet, and green/yellow bicolour. The cable itself is usually printed or marked with “6491B” or “H07Z-R” along its insulation to distinguish it from PVC types.

Physical Form: 6491B is a non-sheathed single core – meaning it consists solely of the insulated conductor with no additional bedding or outer jacket. The finished cable has a relatively small overall diameter. Because the insulation is LSZH, the surface has a slightly different feel than PVC – often a matte finish and a firmer texture.

Electrical Characteristics and Performance

Voltage Rating: The cable is rated 450/750 V (U0/U). This means it can be used in AC circuits up to 750 V phase-to-phase, or 450 V phase-to-earth. It is suitable for the typical low voltage mains distribution in buildings, with ample voltage headroom.

Thermal Ratings: One advantage of 6491B’s thermosetting LSZH insulation is its higher operating temperature threshold. The continuous operating temperature of the cable is up to 90 °C conductor temperature. The minimum operating temperature is around -15 °C. During short-circuit conditions, the cable can withstand conductor temperatures up to 250 °C.

Current-Carrying Capacity: The current capacity of 6491B cables depends on the conductor size, installation method, and ambient conditions. A 2.5 mm² 6491B in conduit is rated to carry about 30 A in a single-phase circuit. A 16 mm² 6491B can carry roughly 95 A in conduit. These values are referenced from standard installation conditions.

Voltage Drop: The resistance of the copper conductor causes voltage drop along the cable run. For example, a 35 mm² 6491B has a conductor resistance of about 0.524 Ω/km at 20 °C. Lower cross-sections have higher resistance, so voltage drop needs consideration for long runs.

Mechanical Bending Radius: The cable’s flexibility (Class 2 stranded) allows it to be bent around corners and pulled through conduit, but minimum bending radii should be observed. As a rule of thumb, for 6491B the minimum bend radius is around 3× the outer diameter for smaller sizes up to 25 mm², increasing to 4× OD for medium sizes and 6× OD for the largest sizes.

Other Characteristics: 6491B is halogen-free and lead-free in its materials, making it environmentally safer and RoHS compliant. It has high dielectric strength and insulation resistance, ensuring safety at the rated voltage.

Advantages of Low Smoke Zero Halogen (LSZH) Insulation

• Minimal Smoke Emission: LSZH cables produce very low smoke when exposed to fire. This greatly improves visibility in a burning building.
• Zero Halogen & Low Toxicity: Burning LSZH emits no hydrochloric acid and far less toxic output, thus significantly reducing health risks.
• Flame Retardancy: Meets IEC 60332-1 requirements for single cable flame propagation.
• Compliance with Safety Standards: LSZH cables comply with strict fire safety standards, often exceeding building regulation requirements.
• Environmentally and Occupationally Safer: No halogenated additives, safer for the environment and for installation workers.

Typical Applications of 6491B Cable

• Conduit Wiring Systems
• Trunking and Ducting
• Distribution Boards & Switchgear
• Lighting Circuits
• Industrial and Plant Wiring
• Airports, Underground & Transportation
• Earthing and Bonding
• Replacement and Upgrades

6491B must be installed in a protected manner – e.g., inside conduit, trunking, or enclosures – because it has no additional outer sheath.

Comparison: 6491B vs 6491X (PVC) and H07V-R Cables

Purchase Information

6491B H07Z-R low smoke cable provides the same electrical performance as standard singles, with vastly improved fire safety. Its LSZH insulation ensures that in the event of a fire, it will limit the spread of flames and reduce smoke and toxic fumes.

Cable Services offers a full range of 6491B cables in sizes and colours to suit your installation needs – all BASEC-approved and compliant with BS and IEC standards.

When safety, compliance, and quality matter – choose 6491B from Cable Services.