You need to set X, Y and set to destination locatio or do some fancy tricks.
If you set only Z then it will go to to point 0, 0, 300 and I think that is not what you want 
You need to set X, Y and set to destination locatio or do some fancy tricks.
If you set only Z then it will go to to point 0, 0, 300 and I think that is not what you want