Why does the differential machine not work with a short circuit?

Question

Cables and wires

I purchased a differential machine model ETI KZS-2M for 25A. Today I decided to check how it will behave in case of a short circuit, as a result: the socket began to melt, sparks flew in all directions, but the machine did not work. The machine is installed at the entrance to a one-story house.
What could be the reason for this behaviour? The TEST button on the machine works properly, but when it is pressed, a glow (like a spark) appears inside the machine, is this normal?
Technical data:
Rated voltage: UN 230 V AC
Rated current: lN 6-40 A
Rated leakage current: IΔN 30 mA
Rated breaking capacity: 10 kA
IP rating: IP 40
Type: A, AC
Tripping characteristic: B, C
Cross-section of connected conductors: 1-25 mm2 max. 3Nm

Answer 1

And diff. the machine must protect against a short circuit !?

Answer 2

The short circuit current might not reach 25 A if the total resistance of the load and wiring was more than 10 ohms. The socket melted, because it is usually designed for a current of 16 A.

Answer 3

@Yekver , well, now let's simulate the situation:
a short circuit occurs in the socket / load of one of the rooms, at which the current reaches 22-24A. Automatic (serviceable) works? No. Is the fire starting? Yes (most likely).
And now the situation is different:
you replaced the machine with 20A. In three rooms, electric kettles of 8A each are switched on. Automatic (serviceable) works? Yes. House without light. Was there an emergency? No.
Do you need an electrician to understand this? ;)