Connecting a new cable - different wire gauge

[timthetoolman]

TL;DR Summary

Cut a cable that has 2 wires connected as a single thicker wire and connect another regular one

Hi.
(not a native English speaker, so apologies in advance for inadequate techical terms)
220V AC, Europe.
There is a cable with 5 wires (2.5mm2 crosssection each) that I would like to cut and make a junction box in the attic to connect another cable to it, to get another outlet. The wires are connected so two of them are live under 25A circuit breaker, two of them are neutral and the fifth is ground. This is an existing feed to the garage that needed more capacity and replacing the whole cable would be a terrible ordeal. There is a separate grounding rod at the cable's destination, so no worries there.
Anyway, when I connect the new cable in the junction box, do i:

a) replicate the same connection, i.e. connect the new cable with 5 wires x 2.5mm2, 2 to the 2 live ones, 2 to neutrals and one grounding

OR

b) take the 3 x 2.5mm2 cable, put a 16A CB and connect one wire to one of the live ones (or both?), same for neutral?

 

[berkeman]

Welcome to PF, Tim.

In the US, and I think in Europe also, we have local regulations about how AC Mains wiring can be used. And when we as homeowners want to modifiy the already-approved wiring in our homes, we need to file for permits and have before/after inspections by the local building departments on our modifications.

This thread is locked temporarily. Please send me copies of your building permit application for the modifications via PM (click on my avatar and Start a Conversation), so I can re-open your thread. Thanks.