Hopefully just the black wires are on the breaker. Two circuits on one breaker. Shouldn't be a problem. It would depend on how many outlets or lights were on the breaker in total. Even then, there is very little chance of something drawing current from every outlet at the same time.
The only thing is you can't put two wires under one breaker (by code). You would have to wire nut them with a pig-tail then just put the one wire under the breaker.
Ground
At the breaker box the black and white will be on a double-pole breaker (or maybe even two separate breakers). To convert to 110V attach the black to a single pole 15 amp breaker, the white to the neutral bus bar (like all the other whites in there) and the ground to the grounding bar (like the other grounds). Then replace the receptacle with a regular 15amp 110V.
Black. wire goes to breaker, white wire goes to neutral bar, and copper wire goes to ground bar.
There should be two outputs on the 30 A breaker. You will need 10 AWG wire with 3-conductors and ground. Typically the wire colors will be Black, Red, White and (Green or bare). Connect black to one output of breaker and red to other output. Connect white to the white buss bar in main panel and green/bare to ground buss bar. At heater end connect the red and black to the 240 V leads, white to white and green/bare to the heater case.
You don't say "turn off" or turn on". Light should be connected black to black and white to white and ground to ground. If you connect white to ground it will work, but you are then using the ground wire for an unintended purpose. Neutral is bonded to Ground at the panel. Current on ground wire could cause ground loops and may cause GFCI to trip if you have them in your house.
Washing machines in the U.S. operate on 120 volts. That requires a single pole 20 amp breaker and wired with 12/2 w-ground wire. Black to the breaker, white to the neutral bus bar, and copper ground to the ground bus bar.
If you are connecting 120 volts, you connect the black wire to the breaker, white wire to the neutral bar, and ground wire to the ground bar. If you are connecting 240 volts connect the black & white wires to the breaker, & ground wire to the ground bar.
There is 220 volts between the two poles. If you are running 2 wires (black and white) + ground then you hook black to one pole and white to the other. Put red or black electric tape on each end of the white wire and wrap around wire for 3 inches or so next to the connection so the next person will be able to see that the wire is hot and not a neutral.
Ground wire connects to the ground bar, white wire connects to the neutral bar, and black wire connects to the breaker. Be sure and turn off main breaker before installing the wire or the breaker.
Ground
At the breaker box the black and white will be on a double-pole breaker (or maybe even two separate breakers). To convert to 110V attach the black to a single pole 15 amp breaker, the white to the neutral bus bar (like all the other whites in there) and the ground to the grounding bar (like the other grounds). Then replace the receptacle with a regular 15amp 110V.
Assuming the wires are the correct gauge for application and breaker you use black and white wires as hot. Put red electrical tape on each end of white wire and connect red and black to the breaker output and bare wire to ground lug in panel. At receptacle connect black and red to hot contacts and bare wire to ground lug.
Black. wire goes to breaker, white wire goes to neutral bar, and copper wire goes to ground bar.
Typically the black wire is "hot", and the white wire is neutral. A 2 pole breaker is most commonly used for 240 V, and as such, you would typically use a 3 conductor wire, with black, red and white (+ ground). In a typical application, the black and red are used in the 2 pole breaker, and neutral is connected to the neutral bar in the breaker panel.
Most likely the ground (green) wire is mistakenly connected to hot instead of the hot wire (black) at the breaker panel! Possibly you meant the neutral wire not the ground wire, in that case most likely the neutral (white) wire is mistakenly connected to hot instead of the hot wire (black) at the breaker panel! In either case check all three wires in the breaker panel for that circuit to make sure they are all correctly connected! Black is hot, White is neutral, Green (or uninsulated in some cases) is ground.
This will pull 20 Amps continuous so you will need a 30 A breaker and 10 AWG wire. You would have Black, Red, White and Ground. The 240 V would be on the black and red connected to the output from a two pole 240 A breaker. White would be neutral and green or bare wire would be ground.
There should be two outputs on the 30 A breaker. You will need 10 AWG wire with 3-conductors and ground. Typically the wire colors will be Black, Red, White and (Green or bare). Connect black to one output of breaker and red to other output. Connect white to the white buss bar in main panel and green/bare to ground buss bar. At heater end connect the red and black to the 240 V leads, white to white and green/bare to the heater case.