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Installation Manual
SMA Solar Technology AG
DC-CMB-IA-U10-xx-en
4 Product Description
4.5 String Fuses
The string fuses protect the PV modules of a PV system from reverse currents. Only install string fuses supplied or approved
by SMA Solar Technology AG as accessories for Combiner Box.
Figure 4: Principle of reverse current
A reverse current can occur when different open-circuit voltages are applied to PV modules connected in parallel. In this
event, the reverse current can be much higher than the short-circuit current of the PV modules. The higher the reverse
current, the more the PV modules of the faulty string will heat up. Strong heat build-up can destroy the modules of the
faulty string.
A reverse current can be caused by the following:
• a short circuit in one or more modules
• a short circuit in one or more cells in a module
• a double ground fault in a module
• a double ground fault in the cabling
The string fuses trip when the string current is too high and protect the PV modules of the faulty string.
4.6 Overvoltage Protection
The Combiner Box is equipped with a surge arrester for overvoltage protection. The surge arrester protects the inverter
from transient overvoltages. In order to guarantee the overvoltage protection function, the surge arrester must be
connected to the external grounding.
