Electrical Connection
SMA America, LLC
44
SI5048U-TUS121440
Technical Description
The current flowing through the battery cable causes a power loss and a drop in voltage with every
meter of plain battery cable. You can use the following table to find the power loss and voltage drop
associated with different cable cross-sections.
Example:
For a 32.8 ft. (10-meter) distance between the Sunny Island and the battery, at least 65.6 ft. (20 m)
of cable are needed (distance there and back). Using a cross-section of AWG 1/0 (50 mm²),
140 A (current flowing through the battery cable) cause a power loss of 170 W in total and an
effective voltage drop of 1.2 V.
Calculation of the Average Nominal Current of the Battery
You can calculate the average nominal current of the connected battery using the following formula:
I
Bat
= Nominal current of the battery
P
AC
= AC power of the inverter
U
Bat
= Nominal voltage of the battery
η
INV
= Efficiency of the inverter at a given AC power
6.2.3 Cable Protection
In addition to the internal DC circuit breaker, install a separate, external fuse as close as possible to
the battery. Install a suitable fuse plug for the fuse according to the maximum specified DC currents.
Cable Cross-section
Power loss
Voltage drop
AWG 1/0 (50 mm²)
2.6 W/ft. (8,5 W/m)
18 mV/ft. (60 mV/m)
AWG 2/0 (70 mm²)
1.8 W/ft. (6 W/m)
14 mV/ft. (45 mV/m)
DANGER
Electric shock resulting from insufficient protection of the DC lines. Death or serious burns.
• Check whether external line protection is present.
• If no external line protection is present, observe the following:
– Lay the DC cables so that ground faults and short‑circuits cannot occur.
– Install an additional current‑limiting fuse outside of the Sunny Island.
When doing so, observe all applicable local standards and guidelines.
