Greg wrote:

You may be on to it here for I've run into this several time and I had to
move
breakers around to find one that would take the piggy back breaker in a Home
box.



It should be on the label somewhere telling you which slots will take the
tandem. Some panels will not take them at all.


My Bryant 200 amp panel label indicates the duplex slots by a dashed
line through the slot boxes.
________
| _ _ _ |
|_______ |