I installed a cat 5 cable as part of a proposed dimming system in my newly refubed kitchen. Problem is that I cant afford dimmer pack at the moment. Missus D is not making tea any more! I though I might stick a few relays in a box in the meantime and control them using the cat 5. Cant find any info on net on current carrying capacity probably because they were not designed to carry current per se.
CAT5 is definitely overkill, but widely-available. I am sure that's the primary reason. Unless there's a very unusual need, all telephone/data wiring is 24 gauge. The exception is CAT6, which is 23 gauge.
22 gauge was the norm for surface wiring that was run around baseboards to make it more resilient to damage during installation.
Regardless, it's more than enough to handle the small control circuit loads as Paul mentioned.