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PV Array Current & OCPD

NEC 690.8 · 690.9 · Conductor & Overcurrent Sizing

When to use: Sizing PV source/output circuit conductors and overcurrent protection. Per NEC 690.8(A)(1) the maximum circuit current is Isc × 1.25 (irradiance factor). Per 690.8(B)(1) conductors and OCPD are sized at 125% of that (continuous duty) — an effective 1.25 × 1.25 = 1.5625× factor on Isc.

Array Parameters

Module Short-Circuit Isc

Parallel Strings

Temp Correction≤ 1.0

Conduit Fill Factor≤ 1.0

Calculation Steps

Array Isc = 9.5 × 3 = 28.50 A

690.8(A): × 1.25 = 35.63 A

690.8(B): × 1.25 = 44.53 A

÷ derate (88%) = 50.60 A min table ampacity

Required OCPD Rating

45A

Next standard fuse/breaker (240.6)

Results

Array Isc (combined)28.50 A

Max Circuit Current (690.8A)35.63 A

Required Ampacity (690.8B)44.53 A

Min Table Ampacity50.60 A

OCPD Rating45 A

NEC References

NEC 690.8(A)(1) — Isc × 1.25 irradiance

NEC 690.8(B)(1) — 125% continuous

NEC 690.9 — Overcurrent protection

NEC 240.6 — Standard OCPD ratings