In Michigan all receptacles within 6' of water require gfci protection. This includes dishwasher and disposal. I ran a multi-wire for those 2 circuits. I forgot about the GFCI requirement and failed inspection. I figured I'll just spend the $100 on a 2p15a gfci breaker and call it good. Well.... I failed again! err, darn it!
I called the inspector and he said gfci breakers don't work on multi-wire. Stating that there will be a different draw on each leg and it will trip. I told him ok I didn't know that, I will research that and correct the violation.
I thought there were some 120/240 GFCIs. What do they use on spas? They typically have L/L and L/N loads. You might also find out they have them but not for your panel. This is the time to talk to your supply house.
"GFCI receptacles can be used on multiwire circuits, but they must be wired such that the neutral on the load side of the GFCI is not shared by two ungrounded conductors. Failure to observe this requirement will result in a differential current any time a load served by an ungrounded conductor not connected to the GFCI is energized, immediately tripping the GFCI.
Note that multipole GFCI circuit breakers are available for use on multiwire circuits. The GFCI sensor mechanisms in these breakers operate on the same principle as the GFCI receptacle, except that the current from all ungrounded conductors and the neutral pass through the "adding machine." As in the case of the receptacles, the unit will trip when it detects unbalanced current over the 4mA to 6mA trip range."
Not sure if the breaker I used is a true multi-pole, the 120/240v seems like it is.
I have not responded until now, as it's been a decade since I installed a 2-pole GFCI breaker.
I had a little confusion installing that one; what I thought was a 'ground wire' on the circuit really needed to be treated as neutral, and pass through the breaker. (The receptacle was a 3-prong style).
I'd venture that if the breaker has a neutral terminal, it can handle single-pole loads. The internals appear to 'do the math.'
The only 'joker' is that the breaker likely has only one neutral connection; you'll need to combine your circuit neutrals before they get to the breaker. A pigtail and wire nut will suffice.