Originally Posted by twd000
This subpanel is being fed with a 50A breaker. The 8/3 feeder cable is Type NM-B
Be careful of that 50A. 8/3-W/G is usually derated to 40A.
"Type NM-B (nonmetallic-sheathed cable) may be used for both exposed and concealed work in normally dry locations at temperatures not to exceed 90°C (with ampacity limited
to that for 60°C conductors) as specified in the 2011 National Electrical Code."
OK, you will loose a full size single 20A breaker; opening a spot for the 'quad'.
But you'll gain (2) 20A-single and (1)30A/2-pole.
The outside breakers work independent of any other breaker in the quad.
You can even use two quads if you want.
15A-2x30A-15A and then 20A-2x30A-20A
(This is assuming the quads will fit your panel)
So far, all your options are still on the table. Just be careful loading that 8/3 past 40A. There is some safety factor built in, but any extended duration full load is going to heat up that feed wire.