I have a 240V subpanel on one side of my house which is fed from a main panel on the opposite side of the house. It is on a 100A breaker. This subpanel is full, with 2 50A breakers and a 30A breaker to an oven and 2 A/C condensers. I would like to somehow add a 20A breaker to this circuit to power a small 240V mini split A/C unit for my office, if possible.
The questions: Can the existing 100A circuit feeding this subpanel handle another 20A circuit? If so, would I need to add an additional subpanel fed by this one? Not to sound stupid, but is there a way to safely add it to the existing subpanel with some kind of tandem breaker or something? Maybe this: HOMT220230CP?
Edit: Spec plates (what I could find anyway...)
The mini-split hasn't arrived yet but here is a link to the listing which has some technical specs: SENL-12CD/220/X