Fire Resistant Cable BTTRZ 4x50mm²+1x25mm² Mineral Insulated 0.6/1kV

Technical Datasheet — BTTRZ 0.6/1 kV 4×50 mm² + 1×25 mm²

Cable Designation & Meaning

Construction: Flexible mineral-insulated fire-resistant cable, corrugated copper tube sheath, round profile (5-core)

Note: BTTRZ employs Class 5 fine-stranded flexible copper conductors. Each core is insulated with fire-resistant mica tape plus XLPE (or ceramic silicone rubber). Cores are assembled with mineral fillers and enclosed in a continuously welded corrugated copper tube sheath, which serves simultaneously as armour, water barrier, and PE conductor. The 4+1 configuration is designed for TN-S three-phase five-wire systems; the PE conductor is reduced to 50% of the phase conductor cross-section (50→25 mm²), complying with GB/T 16895 requirements.

BTTRZ 4×50 + 1×25 mm² — Cable Specification & Engineering Data

1. Product Overview & Rating Summary. BTTRZ 4×50+1×25 is a flexible mineral-insulated fire-resistant power cable rated 0.6/1 kV (Um = 1.2 kV) at 50 Hz, built around four 50 mm² tinned-copper Class 5 flexible phase conductors and one 25 mm² neutral/earth conductor. Unlike rigid magnesium-oxide mineral-insulated cables, BTTRZ uses mica-tape wrapped insulation enclosed in a continuously corrugated copper tube, then jacketed in a low-smoke zero-halogen (LSZH) outer sheath. The cable is designed and type-tested to maintain circuit integrity for at least 90 minutes at 950 °C open-flame exposure (GB/T 19216.21 / IEC 60331-21). Finished diameter is about 44 mm and nominal mass about 3000 kg/km (≈ 300 kg per 100 m), supplied on 500 m or 1000 m wooden-steel drums. With four 50 mm² cores loaded, the cable carries about 175 A in free air at 25 °C (engineering estimate), making it the standard fire-rated feeder for emergency and safety-critical power circuits.

2. Layer-by-Layer Construction (Conductor to Outer Jacket).

3. Electrical Characteristics. Each 50 mm² phase conductor is held to a maximum DC resistance of 0.387 Ω/km at 20 °C, rising to about 0.497 Ω/km at the 90 °C operating point. The 25 mm² neutral/earth conductor holds R ≤ 0.741 Ω/km at 20 °C. Every length survives the routine 3.5 kV AC power-frequency proof held for five minutes. Finished-cable insulation resistance remains above 36.7 MΩ·km (mica-rated, very high), and typical figures include per-core capacitance ≈ 0.45 μF/km and 50 Hz AC impedance ≈ 0.387 Ω/km. With four 50 mm² cores energised, reference loading is about 175 A in free air at 25 °C.

Insulation Data

Electrical Parameters

Reference values: 50 mm² at 170 A, 3-phase 400 V → max balanced load ≈ 118 kW. Voltage drop at 170 A ≈ 2.1 V/km per core (≈0.5% per 100 m).

Temperature Characteristics

4. Thermal Response & Fire Behaviour. Mica insulation sustains a 90 °C continuous conductor temperature, with short-circuit capability up to 250 °C for ≤ 5 s. The cable is rated for service ambients between −15 and +70 °C. The defining property is fire resistance: under GB/T 19216.21 / IEC 60331-21, the cable maintains circuit integrity at rated voltage for at least 90 minutes when directly exposed to a 950 °C open flame. The corrugated copper sheath provides both a fire barrier and a mechanical shield against flame penetration. The LSZH outer jacket emits low smoke and no acid gas (halogen-free), meeting the requirements for tunnels, metro systems, hospitals and high-rise public buildings.

Fire Performance (BTTRZ — Mineral Insulated)

5. Installation Practice & Handling. Bends must not fall below 15 times the actual outer diameter — about 660 mm for this size. The corrugated copper sheath must be earthed at both ends to provide protective-earth continuity. Special sealing glands and termination kits are required at both ends to keep moisture out of the hygroscopic mica layer — improperly terminated ends are the most common failure point on mineral-insulated cables. Reels held below 0 °C in storage must be warmed indoors before uncoiling. The 175 A reference requires derating whenever ambient temperature, grouping or burial depth deviates from reference conditions. Because the cable weighs about 300 kg per 100 m, drum jacks and rated pulling gear must be used.

Technical Datasheet — BTTRZ 0.6/1 kV 4×50 mm² + 1×25 mm²

Standard Compliance Note: BTTRZ belongs to the category of flexible mineral-insulated fire-resistant cables​ (GB/T 34926-2017 Flexible Mineral Insulated Fire-Resistant Cables Rated up to 0.6/1 kV). This is a fundamentally different product category from the PVC flexible cords (RVV) discussed earlier. Parameters below are based on GB/T 34926-2017 and typical manufacturer technical data.

Cable Designation & Meaning

Construction: Flexible mineral-insulated fire-resistant cable, corrugated copper tube sheath, round profile (5-core)

Note: BTTRZ employs Class 5 fine-stranded flexible copper conductors. Each core is insulated with fire-resistant mica tape plus XLPE (or ceramic silicone rubber). Cores are assembled with mineral fillers and enclosed in a continuously welded corrugated copper tube sheath, which serves simultaneously as armour, water barrier, and PE conductor. The 4+1 configuration is designed for TN-S three-phase five-wire systems; the PE conductor is reduced to 50% of the phase conductor cross-section (50→25 mm²), complying with GB/T 16895 requirements.

Applicable Standards

• GB/T 34926-2017 — Flexible mineral insulated fire-resistant cables rated up to 0.6/1 kV
• GB/T 3956 / IEC 60228 — Conductors (Class 5 flexible)
• GB/T 19216.21 / IEC 60331 — Circuit integrity under fire (950 °C / 180 min)
• GB/T 17651 / IEC 61034 — Smoke density (low smoke)
• GB/T 17650 / IEC 60754 — Halogen gas emission (zero halogen)
• GB/T 18380.33 / IEC 60332-3-24 — Flame propagation of bunched cables (Category B)

Product Components / Construction (inside → outside)

Dimensional Data

Insulation Data

Electrical Parameters

Reference values: 50 mm² at 170 A, 3-phase 400 V → max balanced load ≈ 118 kW. Voltage drop at 170 A ≈ 2.1 V/km per core (≈0.5% per 100 m).

Temperature Characteristics

Fire Performance (BTTRZ — Mineral Insulated)

Mechanical & Installation Parameters

6. Typical Service Applications. This 4×50+1×25 BTTRZ cable is the fire-rated feeder for life-safety and emergency power systems: emergency lighting and escape-route supply feeders, fire-alarm system main power and control loops, smoke-exhaust and pressurisation fan feeds, fire-pump and sprinkler-pump power circuits, emergency elevator and refuge-floor power feeds, hospital operating-theatre and ICU emergency supply, metro and tunnel emergency power circuits, high-rise building main fire-fighting risers, data-centre backup power and UPS feeders, oil and gas platform and refinery fire-resistant circuits, tunnel and underground-railway power and control cables, industrial oven and furnace auxiliary power where fire risk is high, stadium and large-venue emergency distribution, nuclear power plant auxiliary circuits, and any circuit where continued operation during a 90-minute fire event is mandated by building code. Approved installation methods include cable tray, direct tray in fire-protected zones, and conduit in fire-rated walls.

7. Testing & Quality Assurance Regime. Routine tests on every length include conductor DC resistance verification (50 mm² ≤ 0.387; 25 mm² ≤ 0.741 Ω/km) at 20 °C, the 3.5 kV AC / 5 min withstand, insulation resistance ≥ 36.7 MΩ·km, conductor continuity across all five cores, corrugated copper sheath electrical continuity, and dimensional inspection covering mica ≈ 0.8 mm, Cu sheath 0.3–0.5 mm, LSZH jacket ≥ 1.8 mm and overall diameter ≈ 44 mm. Sample and type tests comprise the 950 °C / 90 min fire-resistance test (GB/T 19216.21), vertical flame spread GB/T 18380.34 class A, smoke density GB/T 17651, halogen acid gas content GB/T 17650, sheath moisture-tightness / water-immersion leak test, bending at ≥ 15 × OD, short-circuit to 250 °C, and voltage re-test after fire exposure. A factory test certificate accompanies each drum.

Cable Parameters

Cable Test Parameters

Cable Cross Section Structure

Cable Construction Description

Cable Construction Description

8. Standards & Conformity. Design and production are governed by GB/T 19216.21 / IEC 60331-21 for fire-resistance (950 °C / 90 min), GB/T 19666-2019 for flame-retardant and fire-resistant cable classification, and GB/T 12706.1-2020 for low-voltage power cables at 0.6/1 kV. Conductors satisfy GB/T 3956 Class 5. General test methods follow GB/T 19216 series and GB 5023. Surface marking complies with GB/T 6995. The LSZH jacket meets halogen-free requirements per GB/T 17650. Cables can also be supplied to IEC 60331, BS 5839, BS 7621 or NEK 606 requirements on request.

9. Packaging, Storage & Logistics. Standard delivery is 500 m or 1000 m per wooden-steel drum, with bespoke cut lengths available on request. Each drum carries type, voltage, size, supplier identity, production year and sequential metre marking per GB/T 6995. Storage should be in dry, covered premises at −15 to +40 °C, shielded from direct sunlight, moisture, oils and sharp objects; drum end seals must remain intact until installation. Because mica is hygroscopic, any drum whose end seal has been damaged must be re-tested for insulation resistance before use. During transit, drums must be secured against rolling and impact.

10. Procurement Specification. State "BTTRZ 0.6/1 kV 4×50+1×25" together with the required length or drum arrangement, and specify whether the corrugated copper sheath is to be used as the protective earth (PE) or whether a separate green-yellow 25 mm² conductor is required. Always order the matching sealing gland and termination kit at both ends. Always request the factory test certificate, which must include the 950 °C / 90 min fire-resistance report, to confirm the actual diameter (≈ 44 mm), weight (≈ 3000 kg/km) and conductor resistances for the production batch.

11. Cable Industry FAQ.

• Q1: What does "BTTRZ" actually mean? B = fixed-installation wiring cable; T = copper conductor (tinned); T = mica-tape insulation; R = flexible (corrugated, not rigid magnesium-oxide); Z = fire-resistant (circuit integrity maintained under flame). It is the Chinese designation for a flexible mineral-insulated fire-resistant cable, equivalent to BTTW or YTTW in parallel naming systems.
• Q2: How is BTTRZ different from rigid BTTZ (magnesium oxide) cable? Rigid BTTZ uses magnesium-oxide powder packed around solid copper conductors inside a solid copper tube — it cannot bend on site. BTTRZ uses mica-tape insulation on flexible Class 5 stranded conductors inside a corrugated (spiralled) copper tube, so it bends on site like a normal cable and does not require special installation skills.
• Q3: What does "950 °C / 90 min" actually guarantee? During the GB/T 19216.21 / IEC 60331-21 test, the cable is laid in a test furnace, energised at rated voltage, and directly exposed to a 950 °C flame for 90 minutes. The cable must continue to carry the load without electrical breakdown. This is the rating that justifies its use on fire pumps, emergency lighting and escape-route circuits.
• Q4: Why is the corrugated copper sheath necessary? The copper sheath serves three purposes: (i) it is a physical barrier that prevents flame from reaching the mica layer; (ii) it is a moisture barrier — mica is hygroscopic and must stay dry; (iii) it provides a continuous electrical path that can double as the protective earth (PE), reducing the need for a separate earth conductor.
• Q5: Why is the jacket LSZH (low-smoke zero-halogen) instead of PVC? In a fire, PVC releases dense smoke and hydrochloric acid gas, which are the dominant causes of death in fires (inhalation, visibility loss, corrosion of equipment). LSZH jacket releases low smoke and no acid gas — essential in tunnels, metros, hospitals and high-rise public buildings where evacuation is slow and equipment must be protected.
• Q6: Why must the termination kit be special? Mica tape is hygroscopic: if moisture enters the cable end, the insulation resistance collapses and the cable fails. Standard PVC cable glands are not air- and moisture-tight. The BTTRZ termination kit uses a sealed brass gland with epoxy sealing compound and a heat-shrink boot, keeping the mica layer dry for the design life.
• Q7: Can the copper sheath replace the separate earth conductor? Yes — the corrugated copper sheath is electrically continuous and can be sized as the protective earth (PE), provided its cross-sectional area and fault-current capacity meet the installation code. Many BTTRZ 4+0 designs omit the separate earth core and rely on the sheath, reducing the cable size.
• Q8: Why is this cable so heavy (≈ 3000 kg/km)? Three reasons: 50 mm² copper is dense (5 × 4 × 8.89 g/cm³ ≈ 178 kg/km of copper); the corrugated copper sheath adds another ≈ 1500 kg/km of copper; and the LSZH jacket is compounded with mineral fillers. The result is a heavy cable that needs drum jacks and mechanical pulling.
• Q9: Can BTTRZ be used outdoors or buried directly? Yes — the LSZH jacket is UV-resistant and the copper sheath is an effective moisture barrier, so BTTRZ can be installed outdoors, in trays or directly in buried trenches. Unlike ordinary PVC cables, it does not degrade under fire-adjacent or moisture-exposed conditions.
• Q10: Which tests confirm acceptability on delivery and before energisation? At delivery, verify the factory fire-resistance certificate (950 °C / 90 min), conductor resistance (50 ≤ 0.387; 25 ≤ 0.741 Ω/km), dimensions (≈ 44 mm), and the drum end-seal integrity. After installation, complete an insulation-resistance test, a 3.5 kV AC / 5 min withstand, and verify both ends of the corrugated copper sheath are properly earthed before energising.
• Q11: What service life can be expected? When installed, terminated and operated within the stated temperature, voltage and fire ratings, BTTRZ cable is designed for a service life of around 30–40 years in fixed installation. The two failure modes to watch are moisture ingress through improperly sealed terminations (reduces insulation resistance) and mechanical damage to the corrugated sheath (loss of earth continuity). Both are prevented by correct installation and periodic inspection.