65
EN-US
Criteria for the Proper Selection of String Fuses
DC disconnect re-
quirements
NEC 690.15-18 allows the use of fuse holders as a suitable means of disconnecting PV
arrays for servicing.
Additional DC disconnects external to the inverter may be required by the local authority
having jurisdiction.
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
> 1.56 x I
SC
-I
N
< 2.00 x I
SC
-V
N
≥ 600 V DC
- Fuse dimensions: Diameter 0.41 x 1.38 - 1.50 in. (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.
NOTE! The string fuse size must not be greater than the maximum fuse size rat-
ing 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 suitable for a voltage of 600 V DC.
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