ELK-M1XIN Does it have to be powered from the bus?

Can I power the ELK-M1XIN (Input Expander) from an external power supply or does it have to be from the RS485 Data Bus?
 
Reason being, I have a remote unit in the garage and only a single CAT5E between the buildings. I want to use some of the pairs for other things as  I have a 12+ PSU local to the input expander so it seems like a waste to pull power from the other building. 
 
Cheers

The M1XIN can be powered from an aux power supply.  In theory, the RS485 bus can work with just the two Data A and Data B signals between the M1 and the XIN.  But in practice, you may find that you need a common ground (NEG) signal between the two for it to work reliably.  Without a common ground, the two power supplies can have a difference in what each sees as the 0 volt signal level (i.e. a different ground reference).  If they get too far apart, the RS485 receivers can't detect the signals properly.

I recommend getting a power supply with adjustable output voltage. That will allow you to tweak it a little if needed to overcome a long wire run and match it close to the supply on the M1.
 
Mike.