Installation
3.10 Branch circuit protection of multiple inverters
SINAMICS G120D converter
Getting Started, 07/2016, FW V4.7 SP6, A5E38556189B AA
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Branch circuit protection of multiple inverters
For installations with more than one inverter, the inverters are normally powered from a 400-
V power bus with a T distributor.
Image 3-9 Power supply to an inverter group via a shared 400-V branch circuit
Calculation of the branch circuit protection according to IEC and UL standards
Calculation of the branch circuit protection:
● Add together the rated input currents of the inverter group.
● The sum of all rated input currents must be ≤ 24 A.
● Use one of the following protection devices for the inverter group:
– Fuse or circuit breaker with a rated current of 30 A
– Intrinsically safe circuit breaker with a rated current of 25 A
The branch circuit protection also depends on the following conditions:
● Type of cable routing
● Limit values of the cables and system components, e.g. the T distributor.
● Country-specific regulations
If it is precluded that all of the inverters of a group operate simultaneously, it is permissible to
form larger inverter groups on one 400-V branch circuit. The sum of the input currents of all
inverters must always be less than 24 A.
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