Is a fuse required on every string input of a combiner box?

Per IEC 60364-7-712, string-level overcurrent protection is usually required or must be reviewed when three or more strings are connected in parallel. The exact threshold also depends on the module maximum series fuse rating from the datasheet, cable ampacity and local authority having jurisdiction. With fewer than three strings, omission may be permitted but should still be confirmed.

✓ IEC 60364-7-712✓ IEC 61643-31 SPD✓ IEC 60269-6 gPV Fuse✓ 1000V / 1500V DC✓ 4–24 Strings

Solar Combiner Box Configurator

Enter your total string count, system voltage and string Isc — get a preliminary BOM covering combiner box quantity and spec, per-string fuse rating, DC SPD Ucpv and output isolator. Copy for RFQ in seconds.

OmniSol sources and coordinates PV combiner boxes in 4 to 24-string configurations for 1000V and 1500V DC systems from qualified manufacturers — factory-fitted fuses, SPD and isolators available.

Project Parameters

Total number of strings

Total PV strings across the entire array

System DC voltage

String short-circuit current Isc (A)

From module datasheet — used for fuse and isolator sizing

Module max series fuse rating (A) — optional

From module datasheet. If entered, a warning shows when the calculated fuse rating exceeds this value (IEC 60364-7-712 requirement)

Enclosure IP rating

IP54: dust-protected, splash-proof. IP65: dust-tight, jet-proof. IP66: dust-tight, heavy jet-proof. Most outdoor combiner boxes are IP65.

Strings per combiner box

Auto selects the box size that minimises total box count. Use manual selection for higher per-box utilisation.

Maximum string Voc, temperature-corrected (V) — optional

= module Voc × modules per string × (1 + |tempCoeff%/°C| × (25 − minTemp)). Used for SPD Ucpv per IEC 61643-31 — leave blank for a voltage-class estimate

Include in BOM

Per-string gPV fuse + holder

DC SPD Type 2 (IEC 61643-31)

DC output isolator / disconnect

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Enter project parameters and click Generate BOM

Results include combiner box qty, fuse rating, SPD Ucpv and isolator spec

4-string combiner box

8-string combiner box

12-string combiner box

16-string combiner box

Engineering Notes

1.String fuse rating uses 1.25 × Isc per IEC 60364-7-712 as minimum; must not exceed the module's maximum series fuse current rating from the datasheet. Enter this rating above to enable the compliance check.
2.SPD Ucpv ≥ 1.2 × maximum string Voc (temperature-corrected at lowest site temperature) per IEC 61643-31. Enter the temperature-corrected value for a calculated Ucpv; otherwise a conservative voltage-class estimate is used.
3.DC output isolator rating is calculated from 1.25 × (Isc × stringsPerBox). Pole configuration must be confirmed against the system earthing arrangement — not always 2-pole.
4.String fuse may be omitted when fewer than 3 strings are paralleled per combiner box, subject to module datasheet and cable ampacity confirmation per local code.
5.This tool generates preliminary specifications for RFQ and BOM review only. All values must be verified by a qualified electrical engineer before procurement.

Related Tools & Guides

DC Protection Coordinator

MCB, MCCB & SPD sizing for PV systems per IEC 60364-7-712

PV Cable Voltage Drop Calculator

Compare 4mm², 6mm² and 10mm² cable on run length and current

DC Protection Selection Guide

MCB vs MCCB vs gPV fuse — when to use which

BOS 1500V Selection Guide

Full BOS component selection for 1500V DC PV systems

Frequently Asked Questions

What is a solar PV combiner box?

A PV combiner box collects the DC output of multiple PV strings into a single DC feed to the inverter. It typically contains per-string fuses or MCBs, busbars, a DC SPD and a DC output disconnect. Combiner boxes reduce wiring runs and centralise protection on larger arrays.

How many strings can one combiner box handle?

Standard PV combiner boxes are available in 4, 6, 8, 12, 16 and 24-string configurations. For 1500V DC systems, 4–12 string combiner boxes are most common. For 1000V systems, 8–16 strings is typical. The choice depends on array size, cable routing logistics and inverter MPPT input count.

Is a fuse required on every string input?

Per IEC 60364-7-712, string-level overcurrent protection is usually required or must be reviewed when three or more strings are connected in parallel. The exact threshold depends on module maximum series fuse rating, cable ampacity and local AHJ. With fewer than three strings, omission may be permitted but should still be confirmed against the module datasheet.

What SPD rating does a 1500V combiner box need?

Per IEC 61643-31, Ucpv ≥ 1.2 × the maximum string Voc (temperature-corrected at the lowest site temperature). For a 1500V system, Ucpv ≥ 2000V Type 2 DC SPD is a conservative common choice. Enter the temperature-corrected Voc in this tool for a calculated value.

Does OmniSol supply pre-wired PV combiner boxes?

Yes. OmniSol sources and coordinates PV combiner boxes in 4 to 24-string configurations for 1000V and 1500V DC systems, with or without integrated fuses, SPD and DC isolator. Contact us with your requirements for a BOM-matched quotation.