Are there any guide lines for sending voltage down a cat 5e cable?

Yes there are guidelines to how much voltage you can run over CAT5 cable, these guidelines are set out in the specifications in IEEE std. 802.3af-2003 which added clause 33 to the IEEE 802.3 standard. It allows the powering device to use a voltage between 36–57 V DC, though the nominal voltage is 48 V, over two of the four available pairs on a Cat. 3/Cat. 5e cable with a selectable current of 10–400 mA subject to a maximum load power of 15.40 W. If you would like further information, wikipedia is a good source here http://en.wikipedia.org/wiki/Power_over_Ethernet