Garage has 100A service sub-panel from main home. The panel contains a 40A 240V breaker. This connects through a heavy-gauge wire (looks to be same wire as feeding the 100A panel itself) to what I think is only a 15A outlet. That is, based on the physical dimensions and prong arrangement compared to info I found online, I believe this is a NEMA #6-15R receptacle. Am I right?
If the rest of the circuit is 40A but the outlet 15A, then I think this would be undersized and dangerous? Would it be appropriate to replace this #6-15R with a #6-30R? Do I also need to put in a 30A breaker?
The reason this came up is that I would like to use a 20A 240V heater in the garage. The heater uses a #6-30P plug, which can be seen dangling in one of the photos below. Basically, I am looking for a safe way to clean up the electricals, in a way that will make the end result compatible with this NEMA #6-30P heater.