SMA SB 3300TL Installation - Manual (Page 38)

Sizing of a Circuit Breaker SMA Technologie AG
Page 38 SB3300TL-11:SE2006 Installation Guide
Several aspects that have affect on the load must be considered when you select a
circuit breaker. These aspects are specified in the data sheets of the circuit breakers.
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 = 25 A x 0.9 x 0.77 x 1.07 = 18.54 A
The circuit breaker selected for this installation is suitable due to the fact that the ma-
ximum tolerable current of the circuit breaker is above the maximum current of the
used inverter.
As well as the thermal rating of the circuit breakers and all other factors as specified
in section „Sizing of a circuit breaker for the AC line of a photovoltaic inverter for
utility interaction” (page 16), of course the applicable DIN VDE standards
4
also
need to be taken into account. The main ones that apply here are:
• 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
Example for the sizing of a 25 A circuit breaker with B characteristics for the
AC line of a photovoltaic inverter for utility interaction while the circuit breakers
are installed right next to each other without gap (with respect to the thermal
conditions).
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 other stan-
dards may be applicable in special installations.