It is a common error with abbreviations when people use the abbreviation without knowing what the thing means - they end-up using the same word twice.
People habitually say AC current as well, and AC volts which is really nonsense too. It is just habit and convention and is not restricted to science/technical terms.
Additional AnswerIn fact, this is not an error at all. In electrical engineering terminology, the abbreviation, a.c., is considered to be an adjective. So it is both grammatically and scientifically correct to use the expressions "a.c. current" or "a.c. voltage".Of course, if you choose not to use the abbreviation, 'a.c.', then you should say or write "alternating current" or "alternating voltage".
AC current (alternating current) like in a wall outlet
alternating current electricity, or AC current, or AC.
Alternating current aka AC.
This is known as a direct current or DC. The two major types of currents are AC (alternating current) and DC (direct current). In AC the charges move back and forth, but in DC the charges flow in JUST ONE DIRECTION. Due to this characteristic it will not reverse direction like AC can.
AC, Alternating Current.
When electric current changes direction, it is called alternating current (AC).
An "Alternating Current" (AC).
A device called an inverter is used to convert direct current (DC) to alternating current (AC). The inverter switches the direction of the current flow at a rapid rate, creating an alternating current output from the direct current input.
A diode or rectifier converts AC to DC.
alternating current (AC)
An electric current that periodically changes direction is called an alternating current (AC). In AC circuits, the flow of electric charge reverses direction many times per second, typically at a frequency of either 50 or 60 Hz. This is in contrast to a direct current (DC) in which the flow of electric charge remains constant in one direction.
The current you are referring to is called an alternating current (AC). It changes direction periodically to allow for efficient transfer of electricity in power distribution systems.