Some electrical transformers are made for use inside appliances and other devices, but some transformers are made to be portable, external devices. One type sold to help international travelers is sometimes called a voltage transformer. These devices are made to be plugged into the wall socket in an overseas location so you can use American-made electronics requiring 120 volts. Since many destinations in Europe and elsewhere operate on 240 volt current, the voltage transformer is required; otherwise your electronic components would be overloaded. Some of these transformers are "step down" voltage transformers as described above, while "step up" transformers do the opposite. Some of these electrical transformers are made to step up or down, and are the most convenient for frequent travelers.