Combiner Box Design Calculator

Design NEC-compliant combiner boxes for solar PV arrays with proper fusing and ratings.

Number of Strings Strings to combine (2-32 typical)

Modules per String

Module Isc (A) Short-circuit current from datasheet

Module Voc (V) Open-circuit voltage from datasheet

Module Imp (A) Maximum power current

Module Series Fuse Rating (A) From module datasheet

Temperature Correction Factor

Combiner Box Type NEC 690.9 allows unfused for 2-string systems

Environment

NEC Fusing Requirements


                        NEC 690.8: Isc x 1.25 (continuous)

                        NEC 690.9: Fuse >= 1.56 x Isc

                        Fuse <= Module Max Series Fuse

                        Unfused allowed for 2 strings (690.9)

Standard Fuse Sizes

Fuse (A)	Typical Module Isc	Common Use
10A	< 6.4A	Small panels
15A	6.4 - 9.6A	Standard 60-cell
20A	9.6 - 12.8A	72-cell panels
25A	12.8 - 16A	High-current bifacial
30A	16 - 19.2A	Large format

Combiner Box Design Calculator

Combiner Box Specifications

String Fusing

Output Ratings

System Info

NEC Fusing Requirements

Standard Fuse Sizes