Hi everyone, 

with ThinkPad Pro Dock 40A1 I can only connect two external monitors to my T450 at the same time, is that correct? 
https://support.lenovo.com/us/en/solutions/pd029622

I use two external monitors for working and one (tv) for playing games.

What I usually do is connect the TV cable only when I need it and disconnect while working because otherwise the second external monitor is excluded.

Is there a method to keep the third external monitor cable connected, excluding it anyway and to continue to use the other two monitors without problems?

I use Ubuntu as an operating system.

Thanks in advance.

So forgive me reviving an old thread. Become relevant as a charity I'm working with has been donated a number of T440's.

Having bought a 

• ThinkPad Pro Dock (40A1)
  
  I was hoping for 3 displays, but expecting to get only 2.
  
  However I seem to get only one. 
  
  Either DVI or DP, the VGA from the dock seems to be ignored?
  
  Also am I correct in thinking that if I get  a (40A2, I get 3 digital outputs?

  ThinkPad Ultra Dock 90W (40A2) or ThinkPad Ultra Dock 135W, 170W (40A2)

While the Pro Dock (40A1) do support only one digital and one analog external display/monitor, the ultra dock (40A2) supports two digital and one analog display.

You can check the available output configurations here.   You may also want to check the T440 user's guide  (chapter 7).