Our home has a Square D breaker box Cat. No. QO 30HW Series E6 (based on the sticker inside the panel).
It has 30 physical spaces, and the bottom 4 (27-30) have tandem breakers on them. I am looking to add another tandem breaker which as I understand it is acceptable based on info provided in this article provided the box will accept it.
What I do not know is whether my box will accept another tandem switch. Based on this article, the diagram should indicate whether it will accept tandem switches.
However as mentioned, 27-30 already have tandem switches on them, and they work (work = I can independently turn off each switch and only impact that switch).
I cannot seem to find any literature on the box (probably because I don't know what to actually search for). Also, if it will accept another tandem switch, I don't know if it has to be the kind with clips on top and bottom, or if it will take the hook style. Again this might be answered with some literature about the box.
Does the diagram indicate where tandems are acceptable?
EDIT: This is another picture of the diagram in my box. It's about as good as I can get without pulling out the breakers on that side.