Fronius String Control 250/30 DCD DF - Manual (Page 69)

67
EN
Criteria for selecting the right string fuses
General String fuses are used in the Fronius String Control 250/30 DCD DF to provide additional
protection for solar modules.
The maximum short circuit current I
sc
of the solar module is crucial in affording it the correct
fuse protection.
Criteria for select-
ing the right
string fuses The following criteria must be met for each solar module string when selecting suitable fus-
es:
-
I
N
> 1.8 x I
SC
- I
N
< 2.4 x I
SC
- U
N
>/= max. input voltage of the inverter used:
Fronius Agilo .... 1000 V DC
- Fuse dimensions: diameter 10 x 38 mm
I
N
Nominal current of fuse
I
SC
Short circuit current for standard test conditions (STC) according to the solar mod-
ule data sheet
U
N
Rated voltage 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.
Application ex-
ample 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 more than 1.8 times and less than 2.4-times the short circuit current:
-
5.75 A x 1.8 = 10.35 A
- 5.75 A x 2.4 = 13.8 A
Fuse to be selected from the 'Fuses' table:
SPF D 12 with a nominal current of 12.0 A and a nominal voltage of 1000 V AC / DC
NOTE! The nominal current rating of the fuse must not exceed the maximum fuse
protection specified in the data sheet supplied by the solar module manufacturer.
If a maximum fuse protection is not specified, then this information must be re-
quested from the solar module manufacturer.
NOTE! Always select fuses whose rated voltage is greater than or equal to the
maximum input voltage of the inverter used.