Causes and Solutions for Cable Overheating: A Guide for Inverter Users

Root Causes of Cable Overheating

Cable overheating accelerates system aging and may cause fires. Based on field data, we identify five primary causes:

1. Substandard Conductors
   Impure copper (e.g., recycled copper) increases resistance. According to Joule’s law (Q = I²RT), resistance increase causes exponential heat generation.

2. Overloading
   Continuous current exceeding cable capacity is the leading cause. Example:

   2.5mm² cable (rated 26A) powering a 3HP AC (14A) + water heater (10A) = 24A is near its limit.

3. Poor Heat Dissipation

   • Densely packed cables in conduits (fill rate >40%)

   • Ambient temperatures >40°C (e.g., rooftop conduits)

   • Proximity to heat sources (<0.5m)

4. Faulty Connections
   Loose terminals, oxidation, or corrosion at inverter/connector junctions increase contact resistance. These points can reach 100°C+ while normal operation is ≤70°C.

5. Insulation Degradation
   Aging cables (>10 years) develop cracks allowing moisture ingress, causing leakage currents and abnormal heating.

Self-Inspection Guide

Monthly 10-minute checks prevent 80% of failures:

• Visual Inspection
  Check for:
  ✓ Discoloration (yellowing/browning) at terminals
  ✓ Deformed insulation or burnt odor
  ✓ Corrosion on lugs

• Current Measurement
  Use clamp meter to verify load current:

  Example: 4mm² cable max = 32A; if reading >38A → Overload

• Thermal Scanning
  IR thermometer readings:
  ⚠️ >60°C (PVC) or >90°C (XLPE) indicates danger

• Insulation Test
  Megger values:

  • DC strings: Positive-Negative >1MΩ

  • AC output: Phase-Ground >0.5MΩ

Proven Solutions

1. Correct Sizing

Formula: Min. CSA (mm²) = Max Current (A) / Derating Factor
*Factors: Copper=6-8, Aluminum=3-5*

2. Load Management

• Stagger startup of high-power devices

• Balance phases within 10% in three-phase systems

3. Connection Integrity

• Apply torque specified for terminals (e.g., 2.5Nm for MC4)

• Use antioxidant gel for aluminum conductors

• Seal with dual-wall heat shrinks

4. Thermal Optimization

• Maintain cable spacing ≥1× diameter

• Derate 10% for ambient >40°C

5. Quality Cables

• Oxygen-free copper (resistivity ≤0.0172Ω·mm²/m)

• XLPE insulation for DC strings (90°C rating)

• Compliance with IEC 60228 or GB/T 5023

Current Carrying Capacity Table (Copper PVC Cable, 30°C Ambient)

💡 *Power basis: 220V×Current (1-phase), 380V×Current×1.732 (3-phase)*

Inverter Sizing Guide (Copper Cables)

Example: 7kW 3-phase inverter AC current = 7,000W/(380V×1.732×0.8)≈32A → Select 6mm² (47A)

 

Cables are the lifelines of PV systems. Investing in proper sizing + premium cables + scheduled maintenance boosts efficiency by 15%. When selecting inverters, request our free cable sizing tool and thermal inspection protocol to build a future-proof energy solution.