BS 7835 XLPE LSZH 6.35/11 (12) kV Power Cable – Fire Resistant, Low Smoke, Zero Halogen, Underground & Outdoor Use

General Information

Cable Type	BS 7835 XLPE LSZH 6.35/11 (12)kV
Application	Power networks, underground, outdoors, and in cable ducting. Suitable for installations where fire, smoke emission, and toxic fumes create potential threat to life and equipment.
Voltage Rating Uo/U (Um)	6.35/11 (12)kV
Temperature Rating	Fixed: 0°C to +90°C
Minimum Bending Radius	Single core (fixed): 15 × overall diameter 3-core (fixed): 12 × overall diameter Single core 12 × and 3-core 10 × where bends are adjacent to joints/terminations with controlled use of a former

Construction

Component	Material / Details
Conductor	Class 2 stranded copper conductor
Conductor Screen	Semi-conductive XLPE
Insulation	XLPE (Cross-Linked Polyethylene)
Insulation Screen	Semi-conductive XLPE
Metallic Screen	Individual or overall copper tape
Filler	PET fibres
Separator	Binding tape
Bedding	LSZH
Armour	Single core: AWA (Aluminium Wire Armoured) Multi-core: SWA (Steel Wire Armoured)
Sheath	LSZH
Sheath Colour	Red / Black

Standards

Standard Type	References
Cable Standard	BS 7835, EN 60228, IEC/EN 60502-2
LSZH	IEC/EN 60754-1/2, IEC/EN 61034-1/2
Flame Retardant	IEC/EN 60332-1-2, IEC/EN 60332-3-24
Other	UV Resistant

Dimensions

No. of Cores	Cross Section (mm²)	Nom. Diameter Under Armour (mm)	Nom. Diameter Over Armour (mm)	Overall Diameter (mm)	Nom. Weight (kg/km)
1	50	21.7	24.9	28.5	1200
1	70	23.0	26.2	30.0	1500
1	95	24.7	27.9	31.7	1600
1	120	26.7	29.9	33.9	2100
1	150	27.5	31.5	35.7	2500
1	185	29.3	33.3	37.5	2900
1	240	31.6	35.6	40.0	3600
1	300	34.6	38.6	43.0	4300
1	400	37.0	41.0	45.8	5200
1	500	40.5	45.5	50.5	6500
1	630	44.6	49.6	54.8	8000
1	800	48.8	53.8	59.2	9850
1	1000	53.5	58.5	64.3	12100
3	35	41.6	46.6	51.6	4700
3	50	44.4	49.4	54.6	5300
3	70	48.1	53.1	58.5	6300
3	95	52.0	57.0	62.6	7300
3	120	55.6	60.6	66.6	8400
3	150	58.6	63.6	69.8	9600
3	185	62.7	67.7	74.1	11000
3	240	68.1	74.4	81.2	14000
3	300	73.5	79.8	87.0	16600
3	400	78.3	84.6	92.2	20000

Conductor Details

Cross Section (mm²)	Nominal Stranding	Max Resistance at 20°C (Ω/km)
50	19	0.387
70	19	0.268
95	19	0.193
120	37	0.153
150	37	0.124
185	37	0.0991
240	37	0.0754
300	61	0.0601
400	61	0.047
500	61	0.0366
630	91	0.0283
800	91	0.0221
1000	91	0.0176

Electrical Characteristics (Current Ratings)

De-rating Factors

Air Temperature (°C): 25–55

Temp (°C)	25	30	35	40	45	50	55
De-rating Factor	1.00	0.96	0.92	0.88	0.83	0.78	0.73

Ground Temperature (°C): 10–40

Temp (°C)	10	15	20	25	30	35	40
De-rating Factor	1.03	1.00	0.97	0.93	0.89	0.86	0.82

Ground Thermal Resistivity (k·m/W): 0.9–3.0

Resistivity	0.9	1.0	1.2	1.5	2.0	2.5	3.0
De-rating Factor	1.06	1.04	1.00	0.92	0.82	0.74	0.68

Depth of Laying (m): 0.8–2.5

Depth (m)	0.8	1.0	1.25	1.5	1.75	2.0	2.5
De-rating Factor	1.00	0.97	0.95	0.94	0.93	0.91	0.90

In modern power networks, safety, reliability, and environmental compliance are paramount. The BS 7835 XLPE LSZH 6.35/11 (12) kV power cable has emerged as a preferred choice for engineers, contractors, and utility companies, particularly in underground and outdoor installations. This cable combines advanced insulation, fire resistance, and low smoke zero halogen (LSZH) properties, making it suitable for locations where fire hazards pose significant threats to life and equipment.

What Materials Are Used in BS 7835 XLPE LSZH Cables?

The choice of materials is critical for fire resistance, environmental safety, and long-term performance:

Copper Conductors: Class 2 stranded copper offers flexibility and high conductivity.
XLPE Insulation: Cross-linked polyethylene provides thermal stability (0°C to 90°C), chemical resistance, and mechanical toughness.
LSZH Bedding and Sheath: Emits minimal smoke and zero halogen gases during fire, reducing harm to personnel and equipment.
Copper Tape or Wire Armour: Enhances mechanical protection and electromagnetic shielding.
PET Fillers: Maintain roundness, preventing deformation during installation.

The synergy of these materials ensures that BS 7835 cables can perform reliably in high-risk environments such as underground tunnels, industrial parks, and densely populated urban areas.

Where Can BS 7835 XLPE LSZH Cables Be Applied?

BS 7835 cables are ideal for locations where fire safety, low smoke, and minimal toxic gas emissions are critical. Common applications include:

Underground Power Networks: High voltage distribution in tunnels, mines, and subways.
Outdoor Installations: Exposed urban and industrial environments requiring UV-resistant, flame-retardant cables.
Cable Ducting Systems: In commercial buildings, industrial parks, or utility networks where fire safety standards must be met.
High-Risk Facilities: Hospitals, data centers, airports, and petrochemical plants where toxic fumes can cause severe hazards.

Case Study: Indonesia

In Jakarta’s Mass Rapid Transit (MRT) project, BS 7835 cables were deployed for underground power distribution. Engineers prioritized LSZH cables to reduce smoke and halogen emissions, ensuring safe evacuation paths in tunnels during emergency situations. The AWA/SWA armouring provided mechanical protection against accidental digging and vibration from heavy trains.

Frequently Asked Questions About BS 7835 XLPE LSZH Cables

Can BS 7835 Cable Be Buried Directly in the Ground?

Yes, BS 7835 is suitable for direct burial, with proper armouring (AWA/SWA) and bedding. De-rating for soil thermal resistivity must be considered.

Is BS 7835 Cable Suitable for High-Risk Fire Environments?

Absolutely. LSZH insulation and sheath minimize smoke and toxic halogen gas, while flame-retardant XLPE resists ignition. It is ideal for tunnels, hospitals, and data centers.

What Sizes Are Available?

BS 7835 comes in single-core sizes from 50 mm² to 1000 mm² and three-core sizes from 35 mm² to 400 mm², accommodating various current requirements.

How Do I Choose Between Single-Core and Multi-Core?

Single-core: High-voltage transmission, large current capacity, buried or ducted.
Multi-core: Distributes three-phase power with compact installation; preferred in ducted or outdoor areas with controlled layouts.

Can BS 7835 Replace Standard PVC Cables?

Yes, especially in fire-prone areas. Compared to PVC cables like BS 5467, BS 7835 provides better fire resistance, LSZH properties, and UV resistance, though at slightly higher cost.

How Does It Perform in Tropical Climates Like Indonesia?

BS 7835’s thermal rating up to 90°C and UV-resistant LSZH sheath make it suitable for hot, humid climates. Case studies in Jakarta show stable performance underground and in elevated outdoor routes.

Installation Tips and Recommendations

Always plan the route considering bending radius and termination points.
Use suitable LSZH-compatible glands and joints.
Avoid excessive mechanical stress during pulling; use rollers for underground installation.
Apply current de-rating for local ambient and ground temperatures.
Perform insulation resistance tests post-installation to verify cable integrity.

Why Choose BS 7835 XLPE LSZH Cables?

Superior fire safety and reduced smoke/halogen emission.
High mechanical and thermal performance for underground and outdoor use.
Compliance with international and Indonesian standards.
Versatile in industrial, commercial, and public infrastructure projects.
Proven real-world performance in demanding environments such as MRT tunnels and high-density urban areas.

For engineers, contractors, and utility companies seeking reliable, fire-resistant medium-voltage cables, BS 7835 XLPE LSZH 6.35/11 (12) kV offers the perfect solution. Contact your authorized BS 7835 supplier today for technical support, quotations, and installation guidance. Ensure your projects meet the highest safety and compliance standards.