Definition
Overcurrent Protection Device (OCPD) is a fuse or circuit breaker that interrupts current flow when it exceeds a safe threshold. NEC 690.9 sizes OCPD at 1.25 × Isc for PV source circuits.
NEC 690.9 Sizing
OCPD_minimum = 1.25 × Isc (rounded up to standard)Standard OCPD Ratings
15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400 A.
Key Takeaways
- OCPD = fuse or breaker, NEC 690.9 sized at 1.25 × Isc.
- Source-circuit: typically gPV fuse in combiner.
- Inverter output: AC breaker.
- Each parallel string > 2 needs individual fuse.
- Round up to standard rating.
Frequently Asked Questions
4 commonly searched questions about OCPD (Overcurrent Protection Device).
What is an OCPD?
Overcurrent Protection Device — fuse or circuit breaker protecting circuit conductors from overcurrent. For PV source circuits, NEC 690.9 sizes OCPD at 1.25 × Isc.
What's the standard fuse size?
Round up to next standard rating: 15, 20, 25, 30, 35, 40 A. For Isc = 13.5 A: 1.25 × 13.5 = 17 A → 20 A standard.
Fuse or breaker?
PV source-circuit: typically gPV-rated fuse in combiner. Inverter output: typically AC breaker in service panel.
Does each parallel string need its own fuse?
Yes per NEC 690.9 if 2+ strings parallel without overcurrent protection elsewhere.
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