Greg, the ones I have encountered are for air handlers with backup heat are 240V only, so there is no requirement for a neutral. The ones I've seen are 4-circuit panels with 100 amp MLO panels to house two 2-pole breakers. They are all over the place around here. I should have clarified that there are no vacant pole spaces to allow "Harry Homeowner" to add a breaker for a ceiling fan.
Nevertheless, they still are technically sub-panels.
Don't make me go there........
