Undersized DC cables in solar PV systems are one of the leading causes of residential solar fires in Southeast Asia. The Philippine Electrical Code (PEC) 2017 — aligned with NEC Article 690 — has specific requirements for PV wiring. Most homeowners never check if their installer followed them.
DC circuits carry continuous current — unlike AC circuits that have natural zero-crossings. PEC 2017 Section 690.8 requires PV source circuit conductors to be sized at 125% of the module's short-circuit current (Isc). Then apply a second 125% factor for continuous load. Combined: cables must handle 156% of rated Isc.
Formula: Cable ampacity ≥ Isc × 1.25 × 1.25 = Isc × 1.5625
Cable ratings are based on 30°C ambient temperature. Philippine rooftop cable runs regularly reach 50-60°C, which significantly reduces ampacity.
| Ambient Temp | XLPE Cable Derating Factor | Effect on 6mm² cable (47A rated) |
|---|---|---|
| 30°C (base) | 1.00 | 47A |
| 40°C | 0.91 | 42.8A |
| 45°C | 0.82 | 38.5A |
| 50°C | 0.71 | 33.4A |
For a typical 5kW system with 550W panels (Isc ≈ 13.9A per string):
Use the SolarEnergyPH BOM tool to generate a proper Bill of Materials for your installation — cable sizes are automatically calculated based on your system specification.
Engr. Jason Morales — Founder, SolarEnergyPH