Retrofit Precix 3 Axis Gantry Mill

Re. the Einschaltstrombegrenzer -- You can talk to me in german too (probably better in the german subforum) as I'm a fellow austrian.

The magnetic flux in the transformer will try to keep any current flowing while it is collapsing, and can generate more or less unlimited voltages, so turning off inductive loads with SSRs that are not designed to do that can be problematic -- the stored energy in the magnetic field needs to be dumped somewhere.

The tripping of multiple breakers in a row is really suspicious. A B-type breaker takes at least 3-times the rated current for the magnetic disconnect, so 48A. To limit current, you could wire a light-bulb (100W incandescant) in series to the transformer, but I'm not sure if it will survive the shut-off surge so take care. Can you upload your schematics? Maybe the SSR really is the problem even when turning off. Try using a contactor ("Schütz") or for test purposes a manual switch or even bridge it.

Re. safety, maybe you can use a light-curtain ("Lichtgitter", ~500-1k€) in your e-stop loop (with "Schlüsselschalter" to bridge it) -- but those can be problematic if chips can disrupt the beams.

The Servo Power SSR was originally planned also to be controlled by LinuxCNC E-Stop. But as this inductive problems came up i thought maybe leave the toroid on for E-Stop cycles.
The big caps would run the motors for quite some while in case of mosfet shorting out?
So you mean just to add the extreme/min switches to the E-stop. right?

Bin eigentlich "Steirer" living in vienna.
It worked before with ssr for ages, the B breakers trip also on other machines. i will do the schütz thingy for sure. The light bulb comes only when everything fails , but i am optimistic with the schütz. 
Added an image of old ssr/ntc and my scheme... thx 

 

From memory, AC SSR should only switch on at zero crossing, otherwise they blow up.
Not sure if they also switch off at zero crossing, though?

Did a research on this, zero crossing is most common, random switching you hardly stumble upon. Checked mine are 0 crossing. Low chance the blown one was bad fabrication (Chinese)

Chinese SSR if it says 40A, probably 10-15A is OK, above it they usually blow up. Plenty of videos on youtube about exactly that.
Get an Omron one, original if possible!