Electric hypothetical - are these plugs useful?

[Buccaneer]

I have neither the knowledge nor the time/money/whatever to actually move to an electrical setup, but I can see myself going there at some point. I've got a super simple setup right now, but, ultimately, I'm really lazy and having to deal with propane really kinda sucks. Having more exact control of temps and stuff is also appealing to me.

So, while this idea percolates in the back of my mind as a background task, it occurred to me that my house has two unusual plugs. First, I have a NEMA TT-30 (better known as an RV plug). This is quite handy because I have one. The downside is that it's attached to the house and I brew in the detached garage. Not a big deal, though - I'd just need a 30' cord. Second, in the garage I have a NEMA 6-30. No idea whatsoever why the previous owners put that in there.

Are either of these going to be useful to me?

[AllanMar]

The TT-30 as far as I know is 120V 30A. (3600W max)
The NEMA 6-30 is the opposite 240V 30A. (no neutral). (7200W max)
If the wire to the 6-30 has a neutral you could install a NEMA14-30 which is your standard Dryer plug most people use for 30A electric.
The 6-30 would be decent for running heating elements/etc you'd just have to get your 120V (for pumps/etc) from somewhere else.

My guess would be the 6-30 was for a welder?