[HayZee518]

ok, your feeder will be a 10/2 with ground romex. Tape the white wire with a red colored "phase" tape. tape both ends at the appliance and at the panel. something about nomenclature here. romex cable is designated by the number of conductors it carries [minus] the bare ground which is a given. so.....12/2 is two current carying conductors with a bare ground. 10/3 will be two hots, a neutral and a bare ground. FOR YOUR BREAKER for the hot water tank. Purchase a two pole 30 circuit breaker. DON'T get two single pole units. The two single pole units require a tie-bar to be installed on the breaker's handles. Romex can be stapled to the existing joists, but if stapled between the joist surface must be run on running boards. you don't require emt tubing for the installation. the feeder doesn't require a junction box next to the heater. run the cable directly inside the unit. the bare connects to the green screw. a junction box is just another reason for a failure, should any of the splices loosen up. the bare at the panelbox goes to the neutral bar.