22
Criteria for the Proper Selection of String Fuses
Criteria for the
Proper Selec-
tion of String
Fuses
Effects of
Using Under-
rated Fuses
If the fuses are underrated, the nominal current rating of the fuse can be
lower than the short circuit current of the solar module.
Negative effect:
The fuse may open under high irradiance conditions.
Fuse Recom-
mendations
General
The use of string fuses in the Fronius String Control 250/25 US 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.
The following criteria must be fulfilled for each solar module string when
using fuse protection:
-
I
N
> 1.8 x I
SC
-
I
N
< 2.4 x I
SC
-
V
N
≥
max. input voltage of inverter being used:
FRONIUS CL....................................... 600 V DC
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
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.
NOTE
Only select fuses whose nominal voltage is higher or
equal to the max. input voltage of the inverter being used.
You should only use the following fuses, which have been tested by Froni-
us, to ensure problem-free fuse protection:
-
Littelfuse KLKD 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.
Summary of Contents for String Control 250/25
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