Apologies if these questions have been asked before...I've been searching for some time now and believe I know what my plan is, but am curious about a few things.
The previous owners of my house switched the dryer from electric to gas, so I have an unused 10-30R (3-wire 240v) in the basement that's still live. I'd like to use it to power a single 5500W heat stick using these instructions for the control panel: http://www.instructables.com/id/Electric-brewing-system/#intro
Obviously, I need GFCI protection. My understanding is that I can't just switch the breaker in my panel to a GFCI one, as there's no true ground running to it (3-wire outlet). I can't find a 240v 30a GFCI cord under $150 (let alone a 3-wire one), so I was looking at spa panels at home depot.
A few questions:
1) I'd like to plug the spa box into the 10-30R (3 wire). This means the spa box isn't connected to any true ground, but as far as I can tell, this is okay, as the spa box acts as an "effective ground" and if anything shorts the power will "instantly" be cut anyway. Is my understanding of this correct? As far as I can tell, this only actually protects the 240v line such that if I were to use anything that pulls at 120v from the wires I'd need a GFCI for that line as well?
2) As a follow-up to that, "instant" is relative, and I've seen that for it to be safe, the panel would need to trip the GFCI in under 5ms. Is there any way to confirm a given box would do this? None of the boxes on HD's website have anything about a response time. Is this just an industry standard on any new box thus it's not a worry?
3) Any spa boxes I see at HD have max wattages of ~240 watts. This is on a "50 Amp 240 Volt" box. If something's running at 50 amps and 240 volts, that makes it 12000w, which means this box can't handle anywhere near a 5500w heat stick. What does the 240 watt max actually mean then?
4) The spa box is 50amps, but I'm never going to pull more than 30amps from it (all the outlet is anyway). Knowing this, if I'm running 15' of line from the outlet to the spa panel, then 3' of line from the spa panel to my controller, do I definitely need to use #10 wire, or is #12 okay?
5) After all of this, this diagram: http://www.instructables.com/file/FBYO7DFGX5XKQ6Q
will work fine for me, with the exception that going from the 30A breaker into the spa panel is actually only 3 lines?
6) Any reason to not disassemble the spa box, and wire everything (spa box and controller) all in one box?
7) I'm kind of stuck on this page: http://www.homebrewtalk.com/f170/supplying-power-3-prong-range-outlet-371101/index8.html
worrying that this whole thing is still potentially dangerous. What if I used a standard 3-plug cord with the ground connected inside the spa box and the hot and neutral terminated, and plugged the other end into a standard outlet? Would that alleviate the potential code violation? I'm not worried about a fine, I'm worried that the code is there for a reason - safety, and $20 worth of wire would make it a bit safer.