National standard plug size
The national standard plugs are divided into 10A, 16A and 20A. The three sizes are different, 20 are the largest, the next 16, and the smallest of 10A. Each type has a corresponding plug, which can not be mixed with each other.
The middle line is the line drawn from the neutral point of the generator or the power transformer. If it is not grounded, it is called the middle line. If it is well grounded, the middle line will also be called the zero line. Although the zero line and ground line of civil electricity are derived from the same point, their respective functions are separate and can not be mixed. For example, the zero line and the fire line are the electric circuit, they are insulated from the outer part of the electric appliance, the current flowing in the line is the same size, so the wire diameter is the same. And the ground line is connected to the outer shell of the electric appliance. When the electric appliance has trouble, it has the current in the middle of the circuit. The zero line and the fire line are electric circuits, so the zero line can never be connected to the shell, which will make the person electrocuted.