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Criteria for the Proper Selection of String Fuses

Criteria for the

Proper Selec-

tion of String

Fuses

Effects of

Using Under-

rated Fuses

With underrated fuses, the nominal current rating of the fuse is less than

the short circuit current of the solar module.

Effect:

The fuse may blow under intensive irradiance conditions.

Fuse Recom-

mendations -

Application

Example

NOTE! Only select fuses whose nominal voltage is higher or

equal to the max. input voltage of the inverter being used.

Example: Maximum short circuit current (I

) of the solar module = 5.75 A

According to the criteria for selecting the correct fuse, the fuse must have

a nominal current greater than 1.56 times the short circuit current:

5.75 A x 1.56 = 8.97 A

The fuse that should be selected according to the ‘Fuses’ table: KLK D 9

with 9.0 A and 600 V AC / DC

General The use of string fuses in the Fronius String Control 250/25 also adds

fuse protection to the solar modules.

A crucial factor for the fuse protection of solar modules is the maximum

short circuit current I

of the respective solar module.

The following criteria must be fulfilled for each solar module string when

using fuse protection:

-I

> 1.56 x I

-I

< 2.00 x I

-V

≥ max. input voltage of inverter being used:

FRONIUS CL....................................... 600 V DC

....... Nominal current rating of fuse

..... short circuit current for standard test conditions (STC) according to

solar module data sheet

..... Nominal voltage rating of fuse

NOTE! The string fuse size must not be greater than the maxi-

mum fuse current rating of the PV module as provided on the PV

module manufacturers data sheet. If no maximum fuse size is

indicated, please contact the PV module manufacturer.