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Criteria for the Proper Selection of String Fuses
General The use of string fuses in the inverter 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
>/= 600 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
You should only use the following fuses, which have been tested by Fronius, to ensure
problem-free fuse protection:
- Littelfuse KLKD fuses
- Cooper Bussmann PV fuses
Fronius shall not be liable for any damage or other incidents resulting from the use of other
fuses. In addition, all warranty claims are forfeited.
Application Ex-
ample
e.g.: Maximum short circuit current (I
SC
) 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 1.5 times the short circuit current:
5.75 A x 1.5 = 8.625 A
The fuse that should be selected according to the "Fuses" table:
KLK D 9 with 9.0 A and 600 V AC / DC
NOTE! Only select fuses suitable for a voltage of 600 V DC.
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