Every metre of cable has resistance. When current flows through resistance, voltage drops — and that lost voltage means lost power. In a solar system, excessive voltage drop reduces energy production every day for 25 years. The cumulative loss adds up to tens of thousands of pesos.
| Circuit | Standard | Max Allowable Drop | Why Stricter for DC? |
|---|---|---|---|
| DC (PV string to inverter) | AS 4509.2 / NEC 690 | 1% | DC losses are unrecoverable — no transformer to compensate |
| AC (inverter to panel board) | AS 3000 / PEC 2017 | 3% | AC systems can tolerate small drops within code |
| AC (total from meter to load) | PEC 2017 | 5% | Combined subfeeder + branch circuit limit |
For DC and single-phase AC (copper cable, ρ = 0.0175 Ω·mm²/m):
ΔV = (2 × L × I × 0.0175) / A
Where: L = one-way cable length (m), I = current (A), A = cable cross-section (mm²)
| Scenario | Cable | Length | Current | Drop | Result |
|---|---|---|---|---|---|
| PV string (48V DC) | 6mm² | 15m | 13A | 1.14V (2.4%) | ❌ Exceeds 1% — use 10mm² |
| PV string (48V DC) | 10mm² | 15m | 13A | 0.68V (1.4%) | ⚠ Still over 1% — use 16mm² |
| PV string (48V DC) | 16mm² | 15m | 13A | 0.43V (0.9%) | ✅ Within 1% limit |
| AC run (220V) | 4mm² | 20m | 20A | 3.5V (1.6%) | ✅ Within 3% limit |
Calculate your cable voltage drop before buying wire at solarenergyph.shop — the Voltage Drop calculator supports DC, single-phase, and three-phase AC circuits.
Engr. Jason Morales — Founder, SolarEnergyPH