Short-Circuit Current (Isc)

Definition

Isc is the short-circuit current of a PV module at Standard Test Conditions, printed on the datasheet. String current for overcurrent math follows Isc, not Imp. NEC 690.8 sets the maximum circuit current at 1.25 × Isc, and conductors (690.8) and fuses (690.9) are sized at 125% of that, so 1.56 × Isc. Combiner fuses are typically required when three or more strings share a bus. MPPT output current at the battery is still about array watts ÷ battery volts, which is not the same number as module Isc.

Calculators that use this

• Wiring and electrical safety

  Solar Combiner Box Fuse Sizer

  Size PV string and combiner fuses at 1.56 × Isc and see when three or more parallel strings need fusing.

• Inverters and charge controllers

  MPPT Charge Controller Sizer

  Size an MPPT charge controller from array watts and battery voltage, with 20% current headroom and Voc margin.

• Solar panels

  Series vs Parallel Solar Calculator

  Add Voc in series and Isc in parallel to check string voltage, array current and nameplate watts against your MPPT limits.