BTLY-0.6/1kV
BTLY / NG-A Aluminium-Sheathed Mineral Insulated Fire Resistant Cable
A welded aluminium tube gives MI-class fire survival at a fraction of the sheath weight of copper.
BTLY — offered by most Chinese makers under the newer NG-A code — places a continuously welded and corrugated aluminium tube over mica-taped cores with a mineral fill between them. The tube acts as mechanical protection for the fire barrier and as the circuit protective conductor at the same time. Aluminium weighs roughly a third as much as copper per metre of sheath, so a 4 × 25 mm² BTLY run is lighter to handle and to cleat than the BTTZ equivalent, and the corrugation lets it bend tighter than a solid copper tube.
The trade-off is termination discipline. Aluminium does not solder like copper, so the earth connection at the gland must be made with a mechanical lug and antioxidant compound, and buried or permanently wet locations need the oversheathed version rather than a bare tube. Voltcore supplies both forms at 0.6/1 kV, with 6/10 kV and 8.7/15 kV available, and ships matched aluminium-body glands with each drum.
Specification
| Item | Value |
|---|---|
| Rated voltage U0/U | 0.6/1 kV (6/10 kV and 8.7/15 kV on request) |
| Conductor | Plain copper, Class 2 stranded, IEC 60228 |
| Fire barrier | Synthetic mica tape, two layers, minimum 25% overlap |
| Insulation | XLPE, 90 °C continuous, 250 °C short-circuit (≤ 5 s) |
| Isolation layer | Glass-fibre mineral fill and polyester binder tape over the laid-up cores |
| Metallic sheath | Continuously welded, corrugated aluminium tube, 0.6 – 1.2 mm wall |
| Outer sheath | LSZH polyolefin, orange or black; bare-tube version also available |
| Circuit integrity | BS 6387 C/W/Z and BS 8491; GB/T 19216.21 at 950 °C for 180 min |
| Min bending radius | 12 × OD bare tube, 15 × OD oversheathed |
| Cross-section range | 1.5 – 400 mm² single-core; 1.5 – 120 mm² multi-core |
| Earth fault duty | Aluminium tube cross-section stated in mm² on the datasheet for loop impedance calculation |
Layer-by-layer construction
Listed from the conductor outward. Read this alongside the specification table — the two together tell you whether the cable will survive its installation method.
- 1. ConductorClass 2 stranded plain copper, IEC 60228
- 2. Fire barrierSynthetic mica tape, two layers at minimum 25% overlap
- 3. InsulationXLPE, colour-coded, 90 °C continuous rating
- 4. Isolation layerGlass-fibre mineral fill and polyester binder tape over the laid-up cores
- 5. Metallic sheathContinuously welded and corrugated aluminium tube, 0.6 – 1.2 mm wall thickness
- 6. Outer sheathLSZH thermoplastic polyolefin, orange or black; omitted on the bare-tube version
Reference dimensions and weights
| Nominal cross-section (mm²) | Conductor structure (n × mm) | Insulation thickness (mm) | Aluminium tube wall (mm) | Approx. overall diameter (mm) | Approx. weight (kg/km) | Max. DC resistance at 20 °C (Ω/km) |
|---|---|---|---|---|---|---|
| 4 × 4 | 7 / 0.85 | 0.7 | 0.60 | 17.2 | 470 | 4.61 |
| 4 × 6 | 7 / 1.04 | 0.7 | 0.65 | 18.6 | 600 | 3.08 |
| 4 × 10 | 7 / 1.35 | 0.7 | 0.70 | 21.6 | 900 | 1.83 |
| 4 × 16 | 7 / 1.70 | 0.7 | 0.75 | 24.2 | 1300 | 1.15 |
| 4 × 25 | 7 / 2.14 | 0.9 | 0.85 | 28.6 | 1900 | 0.727 |
| 4 × 35 | 7 / 2.52 | 0.9 | 0.90 | 31.6 | 2480 | 0.524 |
| 4 × 50 | 19 / 1.78 | 1.0 | 1.00 | 36.4 | 3350 | 0.387 |
| 4 × 70 | 19 / 2.14 | 1.1 | 1.10 | 41.0 | 4500 | 0.268 |
Reference figures for preliminary sizing and drum planning. Overall diameter and weight vary with strand construction and sheath thickness tolerance; certified drawings are issued with each quotation.
Engineering characteristics
- Welded corrugated aluminium tube carries earth fault current and shields the mica barrier from impact and crushing.
- Meets BS 6387 C at 950 °C for 180 minutes, W with water spray and Z with mechanical shock, plus BS 8491 combined duty.
- Sheath mass is roughly 60% lower than an equivalent copper-sheathed MI cable, reducing support and cleat spacing on vertical risers.
- Corrugated tube bends to 12 × OD, so a fire riser can be routed on site without every bend being pre-formed.
- XLPE insulation gives 90 °C continuous and 250 °C short-circuit ratings, so ampacity follows standard XLPE tables.
- LSZH oversheath keeps acid gas below 5 mg/g and smoke transmittance above 60% where routes pass occupied areas.
- No hygroscopic powder inside: a damaged end does not destroy the insulation resistance of the whole drum length.
Typical applications
- Fire pump, smoke extraction and evacuation lift risers in high-rise residential and commercial towers
- Hospital and airport emergency distribution where long vertical runs make weight a design factor
- Metro and rail tunnel emergency circuits, including wash-down zones
- Chemical and petrochemical plant emergency shutdown and deluge systems
- Battery energy storage and solar sites needing fire-surviving auxiliary power
- Boiler houses and incinerator halls with high ambient temperature
Ordering options
- Bare aluminium tube with no oversheath for dry internal risers where a lighter cable is preferred
- LSZH oversheathed version for buried, wet or chemically aggressive routes
- 6/10 kV and 8.7/15 kV constructions with conductor and insulation screens
- Matched aluminium-body glands, mechanical earth lugs and antioxidant compound kits
- Copper-sheathed BTTZ alternative where the specification forbids aluminium sheaths
Standards manufactured to
- BS 6387 (C/W/Z)
- BS 8491
- GB/T 19216.21
- IEC 60331-21
- IEC 60502-1
- GB/T 13033
- IEC 60754-1
- IEC 61034-2
Manufactured to other standards on request. Send the standard number with your RFQ and we will quote against it rather than against a near-equivalent.
Price and availability for BTLY / NG-A Aluminium Sheathed Mineral Insulated Cable
Include cross-section, core count, voltage grade, route length and installation method — those five determine price more than anything else on the page.
- Engineer-reviewed before pricing
- Reference drawings issued with the quotation
- Free sample up to free sample up to 5 m
BTLY / NG-A Aluminium Sheathed Mineral Insulated Cable — frequently asked questions
Is the aluminium sheath acceptable as the circuit protective conductor?
Yes, provided the gland and earth lug are aluminium-compatible. The tube is continuously welded, so its conductance is known and Voltcore states the sheath cross-section in mm² for loop impedance calculation. Terminate into an aluminium-body gland with antioxidant paste; a copper lug clamped directly onto aluminium forms a galvanic joint and loses continuity over time.
How does BTLY compare with BTTZ on fire performance?
Both are submitted to BS 6387 C, W and Z, and both rely on inorganic barriers rather than polymer survival. BTTZ uses magnesium oxide, which tolerates a far higher continuous temperature: 250 °C against 90 °C for the XLPE in BTLY. BTLY is lighter, bends tighter and installs faster. Where the drawing names MgO insulation, BTTZ is the compliant submission.
Can BTLY be buried directly in soil?
Only the oversheathed version, and only with bedding and warning tape as for any armoured cable. Bare aluminium tube in contact with wet soil or fresh concrete will corrode, so Voltcore supplies the LSZH oversheath plus sealed glands for direct burial. Where ducts or trays are used instead, the bare version is acceptable and saves overall diameter.
Why do some drawings call it NG-A and others BTLY?
They describe the same construction. BTLY was the earlier industry code; NG-A is the shorthand adopted by several Chinese manufacturers for the isolated mineral-insulated, aluminium-sheathed design. Voltcore quotes either name on the datasheet and drum label so the delivery matches the code written into the project documents and the inspection checklist.