I know this is an old thread, but I felt that I should put in my two cents based on real world, on-the-job experience.
An e-call system with smoke warning for senior living facilities which I serviced at my former job used UTP wire exclusively. Either cat3 or cat5. The current draw on the corridor wireless pendant receivers was high enough that the manufacturer recommended pair 1 for the serial data and tripling the power with the remaining 3 pairs. Their engineering department figured the effective gage was nearly 18 awg.