How long meters for RJ-45 cable RS232

Hello, I want use Digi PCI Xp card with RJ45 16 port, and I need know how long maximal cable, can I using for. Our future application is data adquisition from smart card readers.
And I want know if can I use the anny power pin for ourself designed smartcard reader for power suply.
Many thanks.

The amount of distance that RS-232 can be extended depends on the quality of the cable used for the most part, and whether or not its shielded.

Here’s an article about the subject that will give you more detail:

As for the power pin, which pin are you talking about and on which interface (db25/db9/?)?