No. There are no "adaptors". To get 240V from a 120v supply you use a 120-240V step up transformer.
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Clothes dryers, water heaters and and other high-power 240 volt appliances cannot be run on a transformer from a 120 volt circuit. They must be powered from a separate branch circuit that has the right size breakers, cable and socket outlet to suit the appliance.
No, you will need a step down transformer.
NO
A 220 volt line may put out 250 volts because this specification features voltage that varies between 220 and 250 volts. In other countries, the electricity varies in voltage between 110-120 volts.
No, the electrical insulation rating of a 15 amp duplex receptacle is only rated at 130 volts. The 15 amp 240 volt receptacle is rated at 250 volts. The 240 volt receptacle also has a tandem pin configuration instead of the parallel configuration of the 120 volt device. The different pin configuration is so that a 120 volt electrical device can not be plugged into a 240 voltage receptacle.
12 Volts.
No. 140 volts on a 120 volt system is symptomatic of something wrong. On a 120 volt system, 120 volts is near the top end of the acceptable scale with 110 volts being on the lower end of the acceptable scale. The first thing that you should do is check your volt meter against another one to make sure that the readings are the same. Many times meters that get knocked about need to be recalibrated. If you know an electrician check your meter reading against what his shows using a common source of voltage at the time.
A #4 copper conductor will limit the voltage drop to 3% or less when supplying 20 amps for a distance of 250 feet at 120 volts.
P = i*v250w = i * 250vi = 250/120 = 2.08a
Almost every home in north America will have a 240 volt supply (250 volts is the same).
Devices are rated by voltage and amperage. If you have a source rated for 600 volts you can use a 250 volt device, but not vice versa.
12 volts
An adapter can be used. Make sure that the adapter that you use is of a capacity that it can produce the amperage that your appliance needs. An adapter too small will burn itself open and will be of no use to anyone. Remember; Watts = Amps x Volts.
In the US the voltage is about 220 volts. This voltage is based upon the average voltage of the AC sine wave. It can peak as high as 240 volts or as low as 210 volts. So these different voltages are actually referring to an average 220 volt system.