SMA America, LLC
4 Product Description
Installation Manual
CU600-1000US-IA-en-10
17
The minimum size of the string fuses and cables is calculated by means of the short-circuit current
rating (
ISC)
of the PV module. The
National Electrical Code
®
stipulates that all string fuses and cables
are designed to be at least 1.56 times as large as the I
sc
of the PV module being used. The correct
size of the string fuse is determined by calculating the minimum size and then rounding it up to the
nearest standard size for string fuses.
4.5 Reverse Polarity Detection
The SMA Connection Unit 1000-US is equipped with reverse polarity detection.
Figure 5: Reverse polarity detection in the SMA Connection Unit 1000-US
The reverse polarity detection will test if the polarity of the connected conductors is correct once a
string has been newly connected. Testing occurs by operating the integrated button. As long as there
is sufficient DC voltage, the test result is visualized by the LEDs flashing.
Example: calculating the minimum size of the string fuses
For example, if the I
sc
of the PV module equals 6.9 A, then the size of the string fuses is determined
as follows: 1.56 x 6.9 = 10.76
The nearest standard size for string fuses would be a 12 A fuse.
Item
Designation
A
LED for visualizing a polarity-reversed string at
INPUT A
B
LED for visualizing a correct connection for
INPUT A
and
INPUT B
C
LED for visualizing a polarity-reversed string at
INPUT B
D
Button for activating the reverse polarity detection
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