DC Field Box 5 Strings 1000V with Fuses

The Icierre QDC-05/05-1000V-16A-SEZ is a DC field box for PV systems with five independent strings. Each string has its own 1000 V disconnector, its own fuse holder with a 16 or 20 A gPV fuse and its own 1000 V surge arrester; inputs and outputs are brought out on terminal blocks, in an IP66 enclosure with 54 modules.

SEZ or INT version: what changes

The same five-string box comes in two versions. The INT version uses DC circuit breakers and, in the Icierre catalogue, can be combined with a shunt trip coil for remote opening. The SEZ version, the one on this page, separates the two functions: the disconnector opens the string safely, the gPV fuse interrupts an overcurrent.

In practice, the SEZ is the natural choice when no remote trip is required and string-selective overcurrent protection is wanted, with replaceable fuses and clear manual isolation during maintenance. If the design calls for an emergency button that opens the DC side remotely, the INT version is the one to consider.

QDC-05/05-1000V-16A-SEZ features

The string fuse: when it is needed and how to choose it

With five strings kept separate up to the inverter, the fuse does not exist to protect a parallel connection inside the box, because there is none. It becomes decisive when several strings are paralleled on the same MPPT input of the inverter: if one string develops a fault, the others can push a reverse current into it that exceeds what module and cable can withstand. The string fuse interrupts that current before it causes damage.

The rating is not chosen by eye. It must sit above the short-circuit current of the string with the margin required by the design standard (IEC 62548) and must not exceed the maximum series fuse rating stated in the module datasheet. The 16 or 20 A fuses of this box suit conventional-format modules; with large-format TOPCon or HJT modules, whose short-circuit current exceeds 14-15 A, the rating must be recalculated before installation. Replacements must always be gPV DC fuses rated at least 1000 V.

Checking string voltage

The box is rated 1000 V. Many recent inverters accept 1100 V and strings are often designed to use that margin: the open-circuit voltage at the minimum design temperature must stay within 1000 V, otherwise this box is not suitable even if the inverter is.

Frequently asked questions

What is the difference between QDC-05/05 SEZ and QDC-05/05 INT?

The SEZ version uses disconnectors plus gPV fuses on each string; the INT version uses DC circuit breakers, which in the Icierre catalogue can be fitted with a shunt trip coil for remote opening. The SEZ offers overcurrent protection with replaceable fuses; the INT is for when a remote trip is required.

Are 16/20 A fuses suitable for 14-15 A modules?

Not always. The fuse rating must exceed the string short-circuit current with the margin required by IEC 62548 and stay within the module's maximum series fuse rating. With large-format modules, check against the datasheet of the module actually installed.

Does the box parallel the strings?

No. The five strings enter and leave separately: each reaches its own inverter input. Combining several strings on a single pair of conductors requires a combiner box, which has a different function and part number.

Can it be installed outdoors?

The enclosure is IP66, protected against dust and water jets. A position sheltered from direct sun is still advisable: heat build-up inside the box shortens surge arrester life and can affect fuse behaviour.

When should surge arresters and fuses be checked?

During the periodic inspections of the system. Surge arresters are sacrificial components that wear out after significant surges and should be checked via their status indicator; a blown fuse must always be replaced only after finding the cause of the fault on the string.