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Fuse & Breaker Sizing

Overcurrent protection per NEC / IEC.

Electrical

Inputs (SI units)

Results

Minimum rating
31.2 A
Fuse rating
32 A
Breaker rating
32 A

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Engineering Formula

  • I_ocpd ≥ 1.25 (continuous) × 1.25 (PV irradiance) × I
  • = 1.56 × I for PV source circuits

NEC 690.9 mandates 156% multiplier for PV. Non-PV continuous loads use 1.25×. Round up to next standard rating.

Step-by-step Calculation

  1. 1.SizedI × SF31.2 A
  2. 2.Standardnext IEC step32 A

Design Assumptions

  • • Ambient below 40 °C (else derate 0.9× per 10 °C).

Engineering Tips

  • ◆Match string-fuse to module Ifuse rating (typ. 15–25 A).
  • ◆Use gPV fuses for DC PV — NOT gG.

Warnings

  • ▲AC breakers cannot interrupt DC arcs — never substitute.

Standards & References

NEC 690.9IEC 60269-6 (gPV fuses)IS 13703

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