SMA SI 4548-US - Manual (Page 45)

SMA America, LLC 6 Electrical Connection
Operating Manual SI4548-6048-US-BE-en-20 45
6.2.2 Cable Dimensioning
Example for Cable Dimensioning
With a 48 V battery voltage and an outgoing AC power of 4,500 W, a current of up to 100 A flows
through the SI 4548-US-10 battery cable. At the same battery voltage and an outgoing AC power of
6,000 W, a current of up to 130 A flows through the battery cables of the SI 6048-US-10.
The current flowing through the battery cables causes a power loss and a voltage drop with every
meter. Refer to the following table for the power loss and voltage drop associated with different wire
sizes.
Example:
For a distance of 33 ft (10 m) between the Sunny Island and the battery, at least 66 ft (20 m) of cable
are needed (distance there and back). Using a wire size of AWG 2/0 (70 mm²), 100 A (nominal
current of the battery) causes a power loss of 120 W in total and an effective voltage drop of 0.9 V.
Calculation of the averaged nominal current of the battery
You can calculate the averaged nominal current of the connected battery using the following formula:
I
Bat
= Nominal current of the battery
P
AC
= AC power of the inverter
V
Bat
= Nominal voltage of the battery
η
INV
= Inverter efficiency at a given AC power
Keep the cables to the battery as short as possible
The battery cables should be as short as possible. Long cables and insufficient wire sizes reduce
the system efficiency as well as the overload capacities. Do not lay the battery cable under
plaster or in armored conduits.
Choosing the wire size
For cable lengths exceeding 33 ft (10 m), SMA recommends choosing wire sizes greater than
those given by the National Electrical Code
®
310.15.
Wire size Power loss Voltage drop
AWG 2/0 (70 mm²) 1.8 W/ft (6 W/m) 14 mV/ft (45 mV/m)
AWG 3/0 (95 mm²) 1.4 W/ft (4.7 W/m) 11 mV/ft (35 mV/m)