Safety Solar PV

DC Arc Faults: Why Solar Cabling Gets Special Fire-Safety Attention

A sustained DC arc behaves very differently from an AC arc — a genuine reason solar DC circuits get dedicated fire-safety provisions.

DC arc faults get dedicated attention in solar PV codes for a genuine physical reason: DC arcs behave fundamentally differently from AC arcs, and that difference has real fire-safety implications.

Why AC Arcs Are Comparatively Self-Limiting

Alternating current crosses zero amplitude 100 or 120 times per second (depending on frequency), and an arc naturally tends to extinguish at each zero-crossing — giving AC arcs a built-in, repeated opportunity to self-terminate.

Why DC Arcs Don't Get That Opportunity

DC current never crosses zero during normal operation — a DC arc, once established, can sustain itself continuously, burning at extremely high temperature at the fault point until something (a protective device, or the arc physically burning through the conductor) interrupts it.

Where DC Arc Faults Actually Occur in Solar Systems

• Degraded or poorly mated MC4 connectors — the single most commonly cited real-world cause
• Loose terminal screws in combiner boxes or junction boxes
• Cable insulation damage creating a partial fault path

Why This Justifies Dedicated Provisions

This is precisely why arc fault circuit interrupters (AFCI/AFDD-style protection) exist as a distinct requirement for certain PV installations under multiple codes, and why connector quality and correct termination technique get so much emphasis throughout solar installation practice — the consequence of getting it wrong is genuinely different from a typical AC circuit fault.

Engr. Jason Morales — Founder, SolarEnergyPH & OhmWorks

← All articles