Cat7 cable

Are you saying they want to use the brown and blue pair to run a separate physical CobraNet network?  And why do you mention CAT7, are they planning on running 10 gig thru the copper?

If they are just trying to save money, then tell them they could actually save money by running an additional cable, then to take a chance on this trick.

Because yes, I have run two 100 BaseT network connections down a single CAT 5 cable, back when I was doing network cabling.  I know it "can" be done.  It was a case of "we don't have enough room in the conduit to run another cable".

But will it work for CobraNet?  There may be too much crosstalk for this to work.  Keep in mind, when I did this, it was for a pair of computers that could "ask" for another send of the data frame (and the user would not even notice the dropped frames, it happens so fast).  And those computers would rarely be getting traffic down that cable at the same time.  CobraNet would ALWAYS be getting network traffic at the same time, and cannot "ask" for a resend, it just drops the damaged frames.

Would I tell anyone that it WILL work, not a chance.  Especially if it is just to save money.  But IF they are in a bind, and there is just no other way to run another cable, then they can give this a try.  Maybe using a CAT 7 (with the higher twist rate of this cable type) will help with the crosstalk at 100mb enough to work.  It should ONLY be done a last option!