BTTRZ x50mm²+1x25mm² Mineral Insulated Fire Resistant Copper Sheathed Cable for Emergency Power

Cable Designation & Meaning

Construction: Copper conductors, mineral insulation (magnesium oxide or ceramic compound), copper sheath, flexible design with overall LSZH outer sheath.

BTTRZ 4×50+1×25 mm² (flexible mineral-insulated MgO Cu-sheathed fire-resistant cable) — Specification & Engineering Data 

1. Overview & Ratings. BTTRZ 4×50+1×25 — flexible mineral-insulated (MgO) copper-sheathed fire-resistant cable, four 50 mm² copper power cores (L1/L2/L3/N) plus one 25 mm² PE core, embedded in compacted magnesium oxide powder inside a continuous corrugated copper tube, rated 0.6/1 kV; built and tested per GB/T 13033 / BS 6387. The cable maintains circuit integrity at 950 °C for 180 minutes. Ø ≈ 38.5 mm, ≈ 3850 kg/km, wooden drums.

2. Construction Stack (Conductor → Outer).

3. Electrical Characteristics. R ≤ 0.387 Ω/km (50 mm²) / ≤ 0.741 Ω/km (25 mm²) at 20 °C; routine test 3.5 kV AC / 5 min; insulation resistance ≥ 1000 MΩ·km (MgO — extremely high). Reference ampacity ≈ 175 A (4×50 loaded, free air, 30 °C).

Insulation & Sheath Data

Electrical Parameters

Reference values: 50 mm² Cu at 160 A, 3-phase 400 V → max balanced load ≈ 110 kVA. Voltage drop at 160 A ≈ 78.9 V/km per core (≈3.2% per 100 m at 400 V).

4. Thermal & Fire. 105 °C continuous conductor temperature (MgO allows higher than XLPE/PVC); short-circuit 250 °C; fire rating 950 °C / 180 min per BS 6387 class C — the cable remains energised during fire with impact and water spray. Zero toxic gas emission, zero halogen.

Temperature Characteristics

Fire Performance (BTTRZ — Mineral Insulated, Fire Resistant)

BS 6387 Classification:

5. Installation Practice & Handling. CRITICAL: install special MgO end seals at both ends — MgO is hygroscopic and absorbs moisture. Bend ≥ 12 × OD ≈ 460 mm fixed. Use Cu compression lugs + end sealing kits. The Cu tube is the primary fire barrier; the thin PVC outer sheath is only for corrosion protection.

Mechanical & Installation Parameters

6. Typical Service Applications. Fire pump power supply, emergency lighting circuits, smoke control systems, fire alarm circuits, evacuation signalling, critical life-safety power — any circuit that must remain operational during a fire.

7. Testing & QA Regime. Routine: conductor DC resistance, 3.5 kV AC withstand, insulation resistance ≥ 1000 MΩ·km. Type: BS 6387 class C fire test (950 °C / 180 min with impact and water spray), crush resistance, halogen/toxicity test (zero), end seal integrity.

Cable Parameters

Test Parameters

Cable Cross Section Structure

Construction Description

8. Cable Structure Display

9. Packaging, Storage & Logistics. 100 m per wooden drum with sealed ends. Continuous marking: BTTRZ, 4×50+1×25, 0.6/1 kV, 950 °C, GB/T 13033, metre marks. Store dry, indoor, with factory end seals intact.

10. Procurement Specification. State "BTTRZ 4×50+1×25, 0.6/1 kV, 950 °C/180 min" + length. Order matching end sealing kits. Confirm against factory fire test certificate. Do not substitute ordinary YJV for fire-rated circuits.

11. Cable Industry FAQ.

• Q1: What makes BTTRZ fire-resistant? Unlike RVV (PVC insulation which burns and melts at 70 °C), BTTRZ uses magnesium oxide (MgO) — a non-combustible mineral powder — as insulation, and a solid copper tube as the sheath. Neither MgO nor copper burns. The cable can maintain circuit integrity at 950 °C for 3 hours.
• Q2: Why are end seals so critical? MgO powder is hygroscopic — it absorbs moisture from air. If the cable ends are left unsealed, moisture enters the MgO, lowering insulation resistance. Special end sealing kits must be installed at both ends immediately after cutting.
• Q3: What is the difference between BTTZ and BTTRZ? BTTZ uses a solid (non-corrugated) copper tube — rigid, hard to bend. BTTRZ uses a corrugated copper tube — flexible, easier to install. Both are mineral-insulated; BTTRZ is the flexible version.
• Q4: Can BTTRZ be used for normal power distribution? Yes, but it is significantly more expensive than YJV. Use BTTRZ only for fire-rated emergency circuits (fire pump, emergency lighting, smoke control). For normal distribution, use YJV.
• Q5: Why is the cable so heavy (3850 kg/km)? The solid copper tube (≈ 0.9 mm wall over Ø 36.5 mm) is thick copper — much heavier than a PVC sheath. RVV's PVC sheath weighs ~50 kg/km; BTTRZ's copper tube alone weighs ~1500 kg/km.
• Q6: Does BTTRZ need armor? No — the copper tube itself provides excellent crush and impact resistance. This is why it is the standard for fire-rated circuits.
• Q7: What is the maximum conductor temperature? 105 °C continuous (higher than XLPE's 90 °C), because MgO can withstand far more heat. Short-circuit temperature up to 250 °C.
• Q8: Can BTTRZ be buried directly? Yes — the copper tube is water-tight and corrosion-resistant (with the PVC outer sheath). No additional armor needed for direct burial.
• Q9: What is the difference between BS 6387 classes? Class A = 950 °C / 3 hours (highest); Class B = 950 °C / 90 min; Class C = 950 °C / 180 min. BTTRZ meets class C. Class A/B require higher fire ratings.
• Q10: Can RVV be used for fire pump circuits? No — RVV's PVC insulation burns at ~250 °C and releases toxic smoke. Fire pump circuits MUST use mineral-insulated cable (BTTRZ/BTTZ) or fire-rated silicone cable.
• Q11: How do I terminate BTTRZ? Cut the cable square, remove the outer PVC, slide on the end seal gland, fill with sealing compound, install the Cu lug, and crimp. The seal must be moisture-tight. Improper termination is the #1 failure point for mineral-insulated cables.