- 55 -
001050AG
5 - Installation
S
tring Fuse sizing (-S / -SC models)
The correct sizing of the positive side (+) and negative side (-) string fuses
to be used to protect from “return currents” is very important because it
reduces the risk of fire and damage to the PV array.
A “return current” can be generated in the event of a fault and short circuit
at the ends of one or more PV modules. This can result iin all the current
supplied by the strings not involved in the fault, but in the same array, to
pass through the faulty string.
Fuses must be sized for each single string in the PV array. Incorrectly
sized fuses can result in damage to the fuse itself and an inverter
malfunction.
-S models have fuse holders for each individual string conductor pair.
Fuses are sized for single-string currents only. Strings may be not
paralleled in the PV array.
The maximum string fuse size is 20A.
Take into the following two conditions when sizing the string fuses:
1.
The nominal current of the fuse (I
rated
) must not exceed the maximum
series fuse rating found on the PV modules’ technical datasheet and/or
product label. This must be in compliance with standard UL 1703:
I
rated
< Maximum series fuse rating
2.
The fuse rating (I
rated
) must be based on the string current and on the
sizing guidelines provided by the fuse manufacturer to avoid untimely
tripping. As a general guideline, the photovoltaic modules’ short circuit
current (I
sc
) and the following formula give an estimate of the fuse rating.:
I
rated
> 1.25*1.25*I
sc
Fuses must be chosen from among the standard commercially available
ratings, selecting the size that is closest to the calculated value.
N A B C
N A B C
PVS-60-TL-S(-R)-US
PVS-60-TL(-R)-US
PVS-60-TL-SC(-R)-US
42
44
43
34
35
N A B C
N A B C
PVS-60-TL-S(-R)-US
PVS-60-TL(-R)-US
PVS-60-TL-SC(-R)-US
42
44
43
34
35
