ira wrote:If you use 2 breakers and a 4 wire connection to two outlets, one on each phase with a common neutral, you can not use a GFI or ACFI breaker on either of those as the neutral will commonly carry less current than either phase. In that case the safety circuits in the breakers will trigger.

As long as each outlet or circuit has the neutral wire and the phase wire back to the panel I think you should be fine if the breaker is installed correctly.

With two circuits on conventional breakers you typically have the neutrals from both circuits connecting to the common neutral bus bar in the panel, and each breaker only has a single terminal to connect with the phase (hot) wire for that circuit. But if you replace one of these with a GFCI breaker it has an additional neutral pigtail wire for connecting from the breaker to the neutral bar, and has a terminal on the breaker for connecting the neutral from the circuit. So your electrician will first determine which neutral wire on the bus goes to the circuit they are upgrading, and remove that wire from the bus and reconnect it to the breaker, then connect the breaker's pigtail wire to the neutral bar in the panel. Now all current, phase and neutral, from that one circuit go through the GFCI and it works properly.