SMA Solar Technology AG Electrical Connection
Technical Description SI5048-TB-TEN110340 31
6.1 Grounding
Before commissioning the Sunny Island, it must be externally grounded according to the relevant
regulations. To allow different types of grounding, the N connection of the Sunny Island is not
connected to PE at the factory. However, since a connection between N and PE is required for correct
operation, this must be done outside of the device.
Due to filter measures in the Sunny Island, increased leakage currents to PE can always occur. For this
reason, a "fixed terminal" of grounding must be implemented according to EN 50178. Ground the
Sunny Island with a copper conductor (at least 10 mm² cross-section), or with two separate copper
conductors with a cross-section of at least 4 mm² each.
Calculating the Required Grounding Cable Cross-section
SMA Solar Technology cannot provide generally valid values for the cross-section of the cable
required for the external grounding of the battery. The cable dimensions depend on the type and size
of the battery connected, the external fuse (DC side) and the material used in the grounding cable.
The required cross-section of a (copper) grounding conductor can be calculated using the following
formula. Tripping times for short-circuit currents of between 2,000 A and 10,000 A are typically
about 25 ms.
A grounding conductor of 16 mm² cross-section is thus adequate for short-circuit currents up to
10,000 A.
The DC grounding conductors must be connected to the connection labeled "Ground". The grounding
conductor is installed in five steps:
1. Loosen the cable gland on the Sunny Island.
2. Thread the grounding conductor through the cable gland.
3. Remove the protective insulation from the conductor and fit a suitable ring terminal lug to the
exposed end of the conductor.
External grounding
External grounding of the positive or negative pole of the batteries (positive or negative
grounding) is generally possible, because the batteries and the grid side are galvanically
isolated within the Sunny Island. In this case, make sure that the high currents that may
occur under fault conditions can be adequately discharged.
Determining the Cross-section
Exact calculation of the grounding conductor cross-section must take account of the
regionally applicable standards and guidelines.
t = Interruption time in seconds
I
SC
= Maximum battery current (short-circuit current) in
amperes
S = Conductor cross-section in mm
2
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