SMA SB 5000TL Multi-String Installation - Manual (Page 38)

Sizing of a Circuit Breaker SMA Technologie AG
Page 38 SB5000TL-12:SE2006 Installation Guide
One vendor of circuit breakers for example specifies the ratings for an ambient tem-
perature of 50 °C.
Aspects that have an affect on the load specified in the data sheets:
• Reduction of the tolerable current because of continuous load > 1 h = 0.9
1
• Reduction of the tolerable current due to installation of 9 circuit breakers right
next to each other without gap = 0.77 2
• Increase of the tolerable current resulting from ambient temperatures of 40 °C in
the distribution box = 1.07 3
Result:
The nominal current of the circuit breaker is
Inr = 32 A x 0.9 x 0.77 x 1.07 = 23.7 A
The circuit breaker selected for this installation is not suitable due to the fact that the
maximum tolerable current of the circuit breaker is below the maximum current of the
used inverter. It will trip in normal operation.
A solution for this plant would be the installation of the circuit breakers with an 8 mm
gap between each unit. This would result in a reduction coefficient of 0.98 instead of
0.77. This would result in a maximum current of 23.6 A.
Beside the sizing of the circuit breakers in terms of thermal characteristics it is neces-
sary to comply with all other applicable standards
4 . These are especially:
• DIN VDE 0100 Part 410 and/or the international standard IEC 364-4-41:1992
• DIN VDE 0100 Part 430 and/or the international standard IEC 364-4-43:1977
and IEC 364-4-473:1977
• DIN VDE 0298 Part 4
1. In photovoltaic applications continuous loads of over 1 h are possible.
2. The coefficient is 1 in case there is only one single circuit breaker.
3. Resulting from the sizing of the circuit breakers for ambient temperatures of
50 °C.
4. The standards listed here are standards that apply in Germany. Please note
that other standards apply in other countries. Beside the standards above oth-
er standards may be applicable in special installations.