By remodeling my bedroom, I discovered my current tub is using 240v 20A, which are powered by two 12-2 cable. As an update, I don't want a this fancy tub, and also want to add a dryer in my bedroom. However, considering that my bedroom is on second floor and the panel is in the basement, it needs to cut so many thing to run a regular 10-3 wire upstairs. I though of a short cut to use those two 12-2 wire to create a 240V 30A socket which doesn't need a neutral.
So please correct me if I'm wrong. For a dryer which doesn't need a neutral wire in most case (NEMA 10-30 doesn't have neutral), and by the code to run 30A need 10gauge wire. (However most dryer only need 22.5A, as 5400w), I can combine two 12 gauge wire equivalent to 9 gauge in size. I can use each 12-2 cable as one 10 gauge wire to each pole of the NEMA10-30 socket to form a 240V.
Please tell me any danger might happen, or why not to do thing such like this.
Otherwise I can only get a NEMA 6-15 socket which only supports 240V 20A to some smaller ventless dryer which I don't want.
Also, I know code won't allow something like this. But to run a new wire would cost $5000+, which I just want to know are there any risk other than code.
Best Answer
Are you trying to break a record for "most code violations"? Code exist for a reason, the reason is safety. Tech is supposed to serve us, not kill us.
Your entire logic is that "Code is a bunch of nonsense legalese" simply because you don't understand it. No, every rule has a safety reason.
Further, you have a bunch of beliefs that are wrong. And all your beliefs happen to support your plan. Coincidence? Not. You are "making these facts up" to justify what you want you do. That's the road to perdition.
NEMA 10-30 receptacles haven't been legal for 30 years.
Old ones that were installed properly prior to 1990 are grandfathered (you don't need to rip them out) but you're certainly not allowed to install any new ones. All dryers which might plug into a NEMA 10-30 are required to use a 14-30 today, and all are able to do that.
NEMA 10-30 has a neutral. Not a ground.
Neutral is not ground.
The whole problem with NEMA 10-30 is it doesn't have a ground. That pin you think is ground is actually neutral.
All the dryers you think don't need neutral, actually do need neutral. They are using an archaic exception in Code that allows plugging them into legacy NEMA 10-30 sockets if the socket was installed over 30 years ago.
The reason usual/cheap dryers need neutral is they have 120V tumble motor and controls. I don't know why they don't just make those 240V, SMH, but that would cost $10 more, and we can't have that!! They also use electric resistive heat strips to dry the clothes, which is the most expensive and inefficient way to do that thing. Cheap to buy, expensive to run.
If you want hot-hot-ground, use NEMA 6. But most dryers can't use that.
For instance your 12/2 cable could support a NEMA 6-20 recep, which indeed may be able to feed certain high-tech dryers such as the condensing types you don't like for some reason. (perhaps you do not pay the electric bill).
It doesn't cost $5000 to run a branch circuit. 5000 pesos, maybe.
Paralleling is right out.
It requires special equipment on the supply side that is specifically UL-listed for paralleling. That means it needs to meet the safety regs in the UL White Book also. Also paralleling is not allowed below #1/0 wire size (125A), and realistically nobody does it below 4/0 (200A). So you simply won't find appropriate equipment, nor would you want to pay for it if you could.