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How to correctly select wires and cables?
Release time:
2025-03-04
Correctly selecting wires and cables is crucial for ensuring the safe, reliable, and efficient operation of electrical systems. Selection requires consideration of the following core factors to form a systematic decision-making process.
Correctly selecting wires and cables is crucial for ensuring the safe, reliable, and efficient operation of electrical systems. Selection requires a comprehensive consideration of the following core factors to form a systematic decision-making process:
I. Clarifying Application Requirements (First Step)
Application Type:
Power Transmission: Main power lines, equipment power supplies (such as motors), lighting circuits, etc.
Signal/Data Communication: Networks (Ethernet), telephones, audio/video transmission (HDMI), control signals (PLC/DCS), instrument signals, etc.
Special Functions: Fire prevention (flame-retardant/fire-resistant), explosion-proof, high-temperature resistant, anti-interference (shielding), etc.
Installation Environment:
Indoor/Outdoor: UV radiation, temperature differences, rain and snow impact (outdoor requires waterproof, weather-resistant materials).
Laying Method:
Direct Burial Underground: Requires moisture-proof, corrosion-resistant, and mechanical damage protection (armored cables such as YJV22).
Overhead: Requires tensile strength and weather resistance (such as steel core aluminum stranded wire or self-supporting optical cable).
Cable Tray/Conduit: Consider bending radius and heat dissipation (multi-core flexible cables are suitable).
Underwater/Undersea: Special submarine cables (multiple layers of waterproofing, reinforced armor, anti-biological corrosion).
Special Environments: High temperature (boiler room), low temperature (cold storage), chemical corrosion (chemical plant), flammable and explosive (oil depot, mine), electromagnetic interference (near machine room).
Mobility Requirements:
Fixed Installation: Most power cables (such as YJV, VV).
Frequent Movement/Bending: Equipment connection lines, robots, drag chains (high-flexibility cables such as TRVV/PUR sheath).
II. Key Electrical Parameters (Safety Core)
Voltage Level (U₀/U):
Select based on the highest system operating voltage (e.g., 300/500V cable for 220V system, 6/10kV cable for 10kV system). Rated voltage must be ≥ system voltage!
Common Levels: 300/500V (household), 0.6/1kV (low-voltage power), 3.6/6kV~26/35kV (medium-voltage), 64/110kV and above (high-voltage).
Conductor Cross-sectional Area (Core of Current Carrying Capacity):
Calculation Basis: Maximum load current + correction factor (ambient temperature, laying method, number of parallel conductors, etc.).
cosϕ: (Power Factor)
Table Lookup Verification: Select the minimum allowable cross-sectional area according to national standards (such as GB/T 16895.15, IEC 60364-5-52). Do not rely solely on experience estimation!
Voltage Drop Check: Long-distance power transmission requires voltage drop calculation (generally ≤5%), increase cross-section if insufficient.
Current Type:
Alternating Current (AC): Most applications, pay attention to the skin effect (use segmented conductors for large cross-sections).
Direct Current (DC): Photovoltaic systems, energy storage, charging piles (pay attention to polarity, special DC cables such as PV1-F).
III. Conductor and Insulation Material Selection (Performance Basis)
Conductor Material:
Copper: Preferred, high conductivity, good ductility, corrosion resistance (models such as BV, RV, YJV).
Aluminum/Aluminum Alloy: Low cost, light weight, but low conductivity (requires increased cross-section), easy oxidation (requires special terminals). Suitable for long-span overhead lines (such as JL/G1A).
Conductor Structure:
Fixed Installation: Single-core (high current), multi-core (space saving).
Mobile Applications: Stranded conductors (Class 5/6, such as RVVR, TRVV).
Insulation Material:
PVC (Polyvinyl Chloride): General purpose, low cost, good flame retardancy, but low temperature resistance (70°C).
XLPE (Cross-linked Polyethylene): Mainstream power cable, high temperature resistance (90°C), large current carrying capacity, and good aging resistance.
EPR (Ethylene Propylene Rubber): Good flexibility, moisture resistance, suitable for mobile cables.
Silicone Rubber: High temperature resistance (180°C+), used in high-temperature environments (such as heaters).
TPE/TPU (Thermoplastic Elastomer): High elasticity, wear resistance, suitable for drag chain cables.
IV. Sheath and Protective Layer (Resisting Environmental Threats)
Sheath Material:
PVC Sheath: General purpose, mechanical protection, flame retardant (such as VV, RVV).
PUR (Polyurethane): Wear-resistant, oil-resistant, tear-resistant, suitable for robots and drag chains.
LSZH (Low Smoke Zero Halogen): Low smoke and non-toxic when burning, used in subways, hospitals, and airports (such as WDZ-YJY).
Protective Layer Type:
Armor:
Steel Tape Armor (22): Pressure resistance (for direct burial, such as YJV22).
Steel Wire Armor (32/33): Tensile strength (for overhead and underwater use, such as YJV32).
Shielding Layer:
Copper wire braided shielding: Electromagnetic interference protection (instrument cables KVVP, inverter cables BPYJVP).
Aluminum-plastic composite tape shielding: Protection against small signal interference (computer cables DJYVP).
Rodent and ant prevention layer: Special nylon/metal layer (outdoor, substations).
V. Safety Certification and Special Performance (Compliance and Reliability)
Mandatory Certification:
China: CCC certification (wires and cables, flame-retardant/fire-resistant products).
EU: CE certification (CPR fire rating must reach B2/C class), RoHS.
North America: UL/CUL certification (such as UL758, UL1581).
Fire Performance:
Flame retardant rating (IEC 60332):
Single-wire flame retardant (IEC 60332-1) → Bundled flame retardant A/B/C class (IEC 60332-3) (A class is the highest).
Fire resistance performance (IEC 60331): Maintaining power during a fire (90min/750°C or higher, such as NH-YJV).
Other Performance:
Oil resistance: Engineering machinery, gas stations (such as CY cables).
UV resistance: Long-term outdoor exposure (marked UV resistant).
Halogen-free and environmentally friendly: Compliant with RoHS/REACH (preferred for green buildings).
VI. Selection Process Summary (Quick Check Table)
Steps Key Issues
1. Application Power transmission, signal control, or special functions (fire/explosion proof)?
2. Environment Indoor/outdoor? Buried/overhead/underwater? Temperature, chemical corrosion, mechanical stress?
3. Electrical parameters Voltage level? Current size (calculation + table lookup)? Is shielding/armor required?
4. Conductor Copper or aluminum? Single-core or multi-core? Does the cross-sectional area meet the current carrying capacity and voltage drop?
5. Insulation/sheath PVC/XLPE/rubber? Ordinary or halogen-free flame retardant (WDZ)? Is wear resistance (PUR) required?
6. Protection Is armor (pressure/tension resistance) required? Shielding (anti-interference)? Rodent and ant prevention?
7. Certification Does it meet local mandatory standards (CCC/CE/UL)? Does the fire rating (A/B/C class) meet the standard?
8. Cost Under the premise of meeting safety and performance requirements, choose the most cost-effective solution (avoid over-design).
Pitfalls to Avoid:
Strictly prohibit using undersized cables: Insufficient cross-section leading to overheating is the main cause of fire!
Beware of the aluminum-for-copper trap: Aluminum wires require special connectors, and blindly replacing copper wires can easily cause connector failures.
The shielding layer must be grounded: Ungrounded shielded cables will introduce interference!
Fire-resistant ≠ Flame-retardant: Fire-resistant cables ensure power supply during a fire, flame-retardant cables suppress fire spread (important places require both, such as NH-WDZ-YJY).
Avoid non-standard cables: Poor quality insulation materials age quickly and are prone to breakdown and leakage.
Final Suggestions:
Residential/Decoration: Choose BV/BVR (single-core hard wire) conduit, lighting 1.5mm², sockets 2.5mm², air conditioning 4mm², total incoming line ≥10mm²; WDZ-BYJ (halogen-free flame retardant) is preferred.
Industrial power: Mainly choose YJV/YJV22 (XLPE insulation + steel tape armor), shielded cables (BPYJVPP) for frequency conversion equipment.
Data communication: Cat5e/Cat6 shielded twisted pair (FTP), fiber optics preferred.
New energy scenarios: PV1-F for photovoltaic, EV-dedicated cables for charging piles (high specifications for liquid-cooled supercharging).
Be sure to follow national standards (such as GB 50217 "Electrical Cable Design Standard for Power Engineering Projects"), consult professional electrical engineers for complex projects! Safety is paramount, and correct selection is the first line of defense against electrical accidents.
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