SMC Networks Sunny Mini Central SMC 5000A - Manual (Page 46)

Electrical Connection SMA Technologie AG
Page 46 SMC50A_60A-IEN073320 Installation Guide
When selecting line circuit breakers, a number of load factors need to be taken into
account. These can be found in the respective manufacturer's data sheets. For example,
one manufacturer's circuit breaker may be designed for an ambient temperature of 50
°C.
Load factors according to data sheet specifications:
•
Reduction through permanent load >1 h = 0.9
a
• Reduction factor when 9 circuit breakers are arranged side-by-side without gaps
= 0.77
b
• Increase in nominal current as a result of ambient temperatures of 40 °C in the
circuit breaker panel = 1.07
c
Result:
The nominal load current for the line circuit breaker is calculated as:
Ibn = 32 A x 0.9 x 0.77 x 1.07 = 23.7 A
Summary:
The selected line circuit breaker cannot be used in our example case since the maximum
current-carrying capacity for fault-free operation is lower than the maximum output
current of the inverter used.
It will trip under rated operating conditions!
Solution 1:
Use a 35 A line circuit breaker. As a result, the maximum current-carrying capacity
would be 26 A (Ibn = 35 A x 0.9 x 0.77 x 1.07 = 26 A) and the line circuit breaker
will
not trip under rated operating conditions.
However, you should consider the underlying conditions once again! In this case, you
cannot use the previously selected 6 mm² cable anymore.
Solution 2:
Increase the distance between the line circuit breakers to 8 mm. This would mean that
the reduction factor is 0.98 instead of 0.77. As a result, the maximum current-carrying
capacity would be 30 A (Ibn = 32 A x 0.9 x 0.77 x 1.07 = 30 A) and the line circuit
breaker will
not trip under rated operating conditions.
Recommendation by SMA: solution 2
Example for the thermal selection of a 32 A line circuit breaker with B sensitivity
with no gap between the circuit breakers:
a.
Permanent loads of longer than one hour are possible in photovoltaics.
b.
When only one circuit breaker is used, this factor = 1.
c.
Due to the fact that the circuit breakers are rated for 50 °C.