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
AC, or alternating current.AC, or alternating current.AC, or alternating current.AC, or alternating current.
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.
An "Alternating Current" (AC).
It is called an alternating current
There are two types of electric current, DC or direct current and AC or alternating current. The power delivery to homes in most places in the world is AC or alternating current. This is where the electrons are pushed one way then back the other way with usually 100 or 120 changes in direction per second. This produces 50 or 60 forward/back cycles every second called 50Hz or 60Hz.
A diode or rectifier converts AC to DC.
alternating current (AC)
Is called AC voltage or current.