A common symbol for the voltage in a direct current (DC) circuit. In DC circuits, both voltage and current are constant. The "SI" does not allow symbols to be modified with additional information; instead of "12 VDC," write "DC 12 V."
Russ Rowlett (Director), How Many? A Dictionary of Units of Measurement, Center for Mathematics and Science Education University of North Carolina, USA 2005. http://www.unc.edu/~rowlett/units/dictA.html, (Unit of Meas and Covr Factors - Amer) {608}