Different equipment does not only conduct current by conductive materials,but also isolate from conductive parts by insulation materials which limit current circulation in a certain path to keep the people from electric shock. So the conductive materials and insulating materials need to combine for using.
The silver is the best conductive material. Due to the price is too high to use widely. The silver is used in electric contact to shrink the contact resistance of contact. Copper is common conductive materials. Cooper has high conductivity. But if it consist in a little impurity the electrical conductivity decrease a lot. The cable and dynamo coil are made of copper with high conductivity which contains 99.99% copper. The aluminum conductivity is similar to copper. Most transmission lines are made of aluminum or aluminum alloy with steel cores.Some achievements have been made in replacing copper with aluminum in the industries of electric machinery and electric appliances.
The insulation material are not non-conductive absolutely. If insulation materials with high voltage, the insulation materials need to bear high field intensity which may cause the breakdown of insulation material. In order not to make electrical equipment insulation material because of withstand too high electric field strength and breakdown, but also in order not to let the wire through too much current and heat too much, in order to ensure that the load is reliable and economical to work, so allow the voltage value added on each electrical equipment has certain provisions.This specified voltage is usually called the rated voltage of the electrical equipment.Before using any electrical appliances, we must first see whether the rated voltage of electrical appliances with the same supply voltage, if the supply voltage is higher than the rated voltage of electrical appliance. It must not be connected, otherwise, electrical appliances will burn out.If the power supply voltage is lower than the rated voltage of the appliance, it should not be connected, otherwise, the appliance will not work properly.
