NEC 690.8 PV conductor & OCPD sizing
NEC 690.8 sizes PV circuit conductors and overcurrent devices from the module short-circuit current (Isc), with two 125% factors that stack.
The rules
- 690.8(A)(1) — maximum PV circuit current = Isc × 1.25.
- 690.8(B)(1) — the overcurrent device (and conductor ampacity before adjustment) must be ≥ 1.25 × the maximum current, i.e. Isc × 1.25 × 1.25 = 1.56 × Isc.
- 690.8(B)(2) — the conductor must also satisfy the ampacity-after-derating check (temperature + fill) from 310.16.
Worked example: a module with Isc = 13.9 A → max current 17.4 A; OCPD sized to 25 A. A 10 AWG copper conductor on a 45 °C roof with 2 conductors: derated ampacity 34.8 A vs the 21.72 A needed at the 90 °C base — passes.
Related: 690.7 string sizing · 705.12 interconnection.
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