the Circuit Breaker has a switching capacity von 6 kA 

Or do I need to use a circuit breaker with higher switching capacity?

Thanks in advance

I have never seen a MPCB with only 6kA of short circuit protection.

As far as i know when using a combination of protective devices you will need to check the manufacturer backup tables. these tables show how much more short circuit current a device can withstand if it is mounted under another protection.

here is an example:

https://support.industry.siemens.com/cs/us/en/view/109795872

in some cases a device with 6 kA might be considered good up to 50 kA, in others you will need to change it for a more robust solution.

Hallo,

thanks for the answer , i will read the links.

The Datasheet from the MPCB 3VA2110-5MN36-0AA0 (Icu 2,5 kA by 690 Volt)

Product Details - SiePortal - Siemens RC-DE

Best regards