A 90-amp twin breaker fed an HVAC unit of the roof of this condo. The two hots were connected to the breakers in this sub panel. The neutral was not connected to the neutral bus bar. An equipment grounding conductor from that cable was connected to the ground bus. Is the ground carrying the return of the circuit? Doesn’t seem right.
Like the others said, there is NO “return” in a 240v circuit. This is a line-to-line circuit, as opposed to a line-to-neutral circuit. In fact even 120v circuits have no “return”, but that’s another story.
A comment on teminology. The breaker in question is a two-pole breaker, or double pole, or 2-pole. It will NEVER be referred to as a “twin” breaker.
The breaker on the lower left IS a twin breaker, at least here in NY. It will get called many things across the country; twin, skinny, cheater, peanut, and more.
Functionally, it needs one, but there’s no requirement. The equipment could just as easily have a transformer built into it for the 120V loads. Commercial laundry equipment and rooftop air conditioning units often do have a 240x120 control transformer. There is a general prohibition against using the neutral and jumpering it to also serve as the equipment ground, as was once done with ranges and dryers.