Why don't the HOMT tandem breakers fit into all Homeline load

Hi, Re single slot mcb the one shown by beachcomber is an MCB with arc detection there is a IC inside the unit to detect arcing So it requires

Use one load center space with single-pole breakers and two spaces with 2-pole breakers Complete the project: use with Square D circuit breaker accessories

two pair poker The spaces of a QO load center interior that WILL accept QOT type tandem circuit breakers can be identified by rectangular 'slots'(of

two bet poker There are code limits on the number of circuits you can have in one residential panel And remember that both circuits are on the same phase