Fronius DC Box 60/12 MET, Operating Instructions Manual, Page: 53 / 68

51
EN-US
Criteria for the Proper Selection of String Fuses
General The use of string fuses in the Fronius DC Box 60/12 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
SC
of the respective solar module.
Criteria for the
Proper Selection
of String Fuses The following criteria must be fulfilled for each solar module string when using fuse protec-
tion:
-
I
N
> 1.5 x I
SC
- I
N
< 2.0 x I
SC
- V
N
>/= max. input voltage of inverter being used:
Fronius IG 15 - 60 ... 530 V DC
Fronius IG Plus / IG Plus V ... 600 V DC
- Fronius IG-TL ... 850 V DC
- Fuse dimensions: Diameter 10.3 x 35 - 38 mm
I
N
Nominal current rating of fuse
I
SC
Short circuit current for standard test conditions (STC) according to solar module
data sheet
V
N
Nominal voltage rating of fuse
Effects of Using
Underrated Fuses With underrated fuses, the nominal current value may be less than the short circuit current
of the solar module.
Effect:
The fuse may trip in intensive lighting conditions.
Fuse recommen-
dations
For total safety, always use the following fuses, which have been tested by Fronius:
-
Littelfuse SPF fuses
Fronius shall not be liable, and all warranty claims shall be invalidated, for damage or other
incidents that are associated with the use of different fuses.
Fuse Recommen-
dations - Applica-
tion Example Example: Maximum short circuit current (I
SC
) of the solar module = 5.75 A
According to the criteria for selecting the right string fuses, the fuse must have a nominal
current greater than 1.5 times and less than 2.0-times the short circuit current:
-
5.75 A x 1.5 = 8.625 A
- 5.75 A x 2.0 = 11.5 A
Fuse to be selected from the 'Fuses' table:
SPF9 with a nominal current of 9 A
or
SPF10 with a nominal current of 10 A.
NOTE! Always select fuses whose rated voltage is greater than or equal to the
maximum input voltage of the inverter used.