Product Specification

Copper Core 4+1 Cable ZR-YJV 4x50mm²+1x25mm² XLPE Flame Retardant 0.6/1kV

Cable Designation & Meaning

ZR-YJV 4×50+1×25 mm² — Cable Specification & Engineering Data

1. Product Overview & Rating Summary. ZR-YJV 4×50+1×25 sits at the top of the standard 4+1-core flame-retardant range before stepping into the 70 mm² and larger sizes: four 50 mm² annealed copper phase conductors are cabled around a central 25 mm² copper neutral/PE core, each insulated in XLPE and enclosed in a single ST2 PVC oversheath rated for 0.6/1 kV at 50 Hz. Manufacture and type testing are performed to GB/T 12706.1 / IEC 60502-1, stranding complies with GB/T 3956, and the ZR marking denotes class ZC flame retardance under GB/T 19666. The finished outer diameter is roughly 33 mm and the nominal mass is about 2450 kg per kilometre in copper (1150 kg/km for the aluminium YJLV equivalent), delivered in 100 m coils or wooden drums with ≥ Ø 1200 mm flanges — approximately 245 kg per 100 m.

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

3. Electrical Characteristics. Each 50 mm² phase conductor is limited to 0.387 Ω/km at 20 °C, climbing to around 0.49 Ω/km at the 90 °C operating point; the 25 mm² neutral/PE is capped at 0.741 Ω/km. Every production 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, XLPE volume resistivity exceeds 1×10¹² Ω·cm, and typical values include capacitance ≤ 0.38 μF/km, inductance ≈ 0.26 mH/km and 50 Hz AC impedance ≈ 0.40 Ω/km. On a one-second short circuit each 50 mm² phase withstands about 5.75 kA (the 25 mm² neutral on a 2.88 kA basis), using I = k·A/√t with k = 115 for copper/XLPE. With all four phase cores energised, reference loading is 175 A in free air at 25 °C and 145 A directly buried at 25 °C — engineering estimates to be confirmed against the factory test certificate.

Electrical Parameters

Cable Parameters

Cable Test Parameters

Cable Structure Parameters

4. Thermal Response & Flame Performance. XLPE sustains a 90 °C continuous conductor temperature and tolerates a 250 °C short-circuit peak for up to five seconds. The cable is rated for service ambients between −20 and +45 °C, must not be uncoiled below 0 °C without pre-conditioning, and uses 25 °C as the reference soil temperature for buried ratings. Flame behaviour meets class ZC of GB/T 19666, proven by both the single-cable vertical test (GB/T 18380.12) and the category-C bunched test (GB/T 18380.35) with char height limited to 2.5 m. The PVC jacket is halogenated and will emit smoke and acid gas in a fire; low-smoke zero-halogen projects must specify WDZ-YJY instead.

5. Installation Practice & Handling. Bends must not fall below 15 times the actual outer diameter — about 495 mm for this size. Before first energisation, apply the DC site withstand at 4U0 = 2.4 kV for 15 minutes in line with Q/GDW 13244.1-2018. Drums held below 0 °C in storage must be warmed indoors before uncoiling; pulling tension should stay within 8000 N, and for longer runs a powered winch with a proper pulling grip is advisable. The 175 A (air) and 145 A (buried) references require derating whenever ambient temperature, cable grouping or soil thermal resistivity deviates from reference conditions. Crimp lugs, glands and heat-shrink termination kits must be matched to the 9.0 mm phase core, 6.7 mm neutral core and ≈ 33 mm jacket, and both phase and neutral short-circuit withstand should be coordinated with upstream protective device settings.

6. Typical Service Applications. This cross-section serves heavy main and sub-main distribution circuits: main distribution risers in high-rise commercial buildings, transformer secondary feeders up to about 250 kVA, motor connections in the 22–45 kW range, machine-tool and process-line power leads, factory workshop and warehouse distribution panels, elevator and escalator supply circuits, and auxiliary power in light-industrial installations. Approved installation methods include steel or PVC conduit, cable trunking, tray and indoor ducting, both indoors and in covered outdoor locations. For direct burial or mechanically exposed routing, the steel-tape armoured ZR-YJV22 variant is recommended.

7. Testing & Quality Assurance Regime. Routine tests on every length include phase and neutral DC resistance verification (≤ 0.387 / 0.741 Ω/km at 20 °C), the 3.5 kV AC / 5 min withstand, conductor continuity across all five cores and dimensional inspection covering phase insulation ≥ 1.4 mm, neutral insulation ≥ 1.2 mm, sheath ≥ 1.8 mm and overall diameter ≈ 33 mm. Sample and type tests comprise the XLPE hot-set trial at 200 ± 3 °C for 15 minutes under 0.2 MPa (load elongation ≤ 175 %, permanent set ≤ 15 %), XLPE tensile ≥ 12.5 MPa with elongation ≥ 200 %, PVC sheath tensile ≥ 10 MPa with elongation ≥ 125 %, PVC thermal stability ≥ 200 minutes at 200 °C, single-cable and category-C bunched flame trials, and bending assessment. Commissioning on site requires insulation-resistance measurement, the DC 2.4 kV / 15 min withstand and positive L1/L2/L3/N/PE identification before switching. A factory test certificate accompanies each drum.

Cable Insution Parameters

Cable Flame Retardant Parameters

8. Standards & Conformity. Design and production are governed by GB/T 12706.1 and IEC 60502-1 for 0.6/1 kV extruded-insulation power cables. Conductors satisfy GB/T 3956 / IEC 60228 Class 2 — the 50 mm² phase as nineteen wires of 1.78 mm with R ≤ 0.387 Ω/km, and the 25 mm² neutral as seven wires of 2.14 mm with R ≤ 0.741 Ω/km. Flame retardance is classified under GB/T 19666 (ZC as the default for the ZR marking) and proven by GB/T 18380.12 and GB/T 18380.35 category C. Installation acceptance follows Q/GDW 13244.1-2018 and GB 50168, while surface marking complies with GB/T 6995. Cables can also be supplied to IEC, BS, DIN, ICEA or JIS requirements on request. Because the ST2 PVC jacket contains halogen, tunnels, metro systems, hospitals and other confined public areas call for WDZ-YJY.

9. Packaging, Storage & Logistics. Standard delivery is 100 m per coil or wooden drum, with bespoke cut lengths available on request. Each drum carries type, voltage, supplier identity, production year and sequential metre marking per GB/T 6995. Storage should be in dry, covered premises at −20 to +45 °C, shielded from direct sunlight, moisture, oils and sharp objects; coils and drums remain sealed until installation and are stored upright on their flanges rather than flat. In cold conditions, condition drums indoors to ≥ 0 °C before pulling. During transit, coils and drums must be secured against rolling and impact, and the cable must never be dragged across abrasive ground or sharp edges.

10. Procurement Specification. State "ZR-YJV 0.6/1 kV 4×50+1×25" together with the required length or drum arrangement and marking preferences. Specify the flame-retardant class (ZC is standard; ZA or ZB available), jacket colour and any special drum requirements. Always request the factory test certificate to confirm the actual unarmoured diameter (≈ 33 mm), weight (≈ 2450 kg/km) and ampacity for the production batch. Where low-smoke zero-halogen or armoured construction is needed, order WDZ-YJY or ZR-YJV22 respectively.

11. Cable Industry FAQ.

• Q1: How does 4×50+1×25 differ from the smaller 4×35+1×16? The phase area grows from 35 to 50 mm² (conductor from 7×2.52 to 19×1.78 mm) and the neutral from 16 to 25 mm² (7×1.70 to 7×2.14 mm), raising the rated current from about 140/115 A to 175/145 A, increasing the finished diameter from 28.5 to 33 mm, and lifting the one-second phase short-circuit withstand from about 4.03 to 5.75 kA.
• Q2: Why is the neutral/PE only 25 mm² when the phases are 50 mm²? In a balanced four-wire circuit the neutral carries mainly unbalance and harmonic current, so GB/T 12706.1 permits a reduced core in the 4+1 construction. Where the installation serves substantial single-phase or non-linear, harmonic-generating loads, an equal-section 5-core cable should be chosen.
• Q3: What do ZA, ZB, ZC and ZD mean? These are flame-retardant classes in GB/T 19666, assessed through the bunched-cable test GB/T 18380.35 at progressively higher fuel loads — ZA is the most demanding, ZD the least. The bare "ZR" marking defaults to ZC; ZA and ZB must be requested at ordering.
• Q4: When should a 4+1, equal 5-core, or plain 4-core cable be selected? Choose 4+1 for standard four-wire service with a reduced neutral/PE; equal 5-core (4×A+1×A) where neutral current is expected to approach phase current; plain 4-core when no separate PE conductor is required in the cable.
• Q5: Why do air and buried ratings differ, and how are they adjusted? Published figures assume 25 °C air or 25 °C soil at 1.0 K·m/W thermal resistivity with a single circuit. Manufacturer correction factors must be applied for ambient temperature, grouping, burial depth and soil resistivity — air factors range from about 1.29 at 20 °C down to 0.91 at 45 °C, and soil factors from 1.04 at 20 °C to 0.87 at 40 °C.
• Q6: Copper or aluminium? Copper (this cable) delivers lower resistance (0.387 versus roughly 0.641 Ω/km at 50 mm²), higher current per mm², better mechanical strength and more dependable terminations; aluminium (YJLV, ≈ 1150 kg/km in this size) costs less and weighs less but requires larger cross-sections and anti-oxidation treatment at every joint.
• Q7: Why can XLPE run at 90 °C while PVC insulation is limited to 70 °C? Cross-linking transforms polyethylene into a three-dimensional thermoset network, which raises the continuous conductor rating to 90 °C and the short-circuit withstand to 250 °C — directly increasing the ampacity available from a given copper area.
• Q8: How is the conductor cross-section chosen? Selection is governed by (a) full-load current after derating, (b) permissible voltage drop (typically ≤ 5 % for branch circuits), (c) short-circuit withstand on an I²t basis (5.75 kA·s per phase here), and (d) coordination with overcurrent protective devices; the most stringent criterion controls.
• Q9: Why does finished diameter vary between manufacturers for the same nominal size? Standards set minimum insulation and sheath thicknesses plus electrical performance, but not a precise overall diameter. Stranding compaction, filler design and sheath tolerance differ between plants — published 4×50+1×25 figures cluster around 33 mm unarmoured — so the actual measured diameter must always be used when sizing glands, trays and conduits.
• Q10: Which tests confirm acceptability on delivery and before energisation? At delivery, verify the factory test certificate (resistance 0.387/0.741 Ω/km, 3.5 kV/5 min withstand, dimensions ≈ 33 mm), jacket legibility and drum integrity. After installation, complete an insulation-resistance test plus the DC 4U0 = 2.4 kV / 15 min withstand per Q/GDW 13244.1-2018, then confirm L1/L2/L3/N/PE identification before closing the breaker.
• Q11: What service life can be expected? When installed and operated within the stated temperature and voltage limits, XLPE 0.6/1 kV cables are designed for a minimum service life of 30 years; sustained overload, ultraviolet exposure, water ingress through a damaged sheath, or operation above 90 °C will materially shorten that life.