In the connection diagram you can see multiple runs coming from the 1st floor to Tree Extension 1. We’ve numbered it so in total you will see 6 wire runs. You can connect as many runs to one branch as long as the total number of devices on all the runs is not more than 50. So in this example all the runs from 1 to 6 are coming into left branch (square number 1) of Tree Extension 1.
Tree extension 1 still has the right branch (square number 2) available, which is running to the 2nd floor. Remember, never cross the two branches.
Finally, in this example there is another tree extension (Tree Extension 2) which is added to the system for the ability to control another run (run 8) to the 3rd floor. This example assumes that run 7 is going to have the maximum of 50 devices, so therefore another extension is required.