Knowing the next part... 09:12 Nov 20, 2011
...is essential.
There is a rule that, where the wiring cross section changes (that is, downstream in the installation, at every point where the wire gets "thinner" than upstream of this point), there must be a breaker, but this would apply here (for sure) if the wording were "...en un [or "en cada"] cambio de sección" (and adding "de conductores" would not do any harm, either).
As it is, it might mean quite a lot of things, some of which would "collide" with others, thus choosing the wrong one might result in a [potentially bad] slip. | 
The translation workplace 
