cable tension for Shimano 105 Front derailleur is very tight I just got a merida scultura 400 and on the biggest chainring there's rubbing on the outside of the front derailleur cage. the only way that I can lower this is by tightening the cable by ALOT. is this normal on a road bike?
First you should make sure your "high limit screw" is loose enough.  This may be marked H on the derailleur, or it may be one of two adjacent unmarked screws.  By loosening this you allow the derailleur to travel a bit more outboard.

Then, using some combination of adjusting the cable tension with the clamp bolt and with the barrel adjuster, set the tension so that the cage stays outboard enough (but not too much).  On your particular bike the barrel adjuster is inline with the shifter cable near the handlebars.

If your question is whether it's normal for there to be significant tension on the shift cable when the front derailleur is in the outer position, the answer is yes.  This tension must overcome the (fairly strong) return spring in the derailleur.