SMA SMC 5000 Installation - Manual (Page 52)

Sizing of a Circuit Breaker SMA Technologie AG
Page 52 SMC50_60-11: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
a
• Reduction of the tolerable current due to installation of 9 circuit breakers right
next to each other without gap = 0.77 b
• Increase of the tolerable current resulting from ambient temperatures of 40 °C in
the distribution box = 1.07 c
Example for the sizing of a 32 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).
a. In photovoltaic applications continuous loads of over 1 h are possible.
b. The coefficient is 1 in case there is only one single circuit breaker.
c. Resulting from the sizing of the circuit breakers for ambient temperatures of
50 °C.