I am aware that there is a way to append units to the siunitx package, but I wanted to recommend the addition of the unit "ampere."
Please let me know if it is already in the package and I haven't seen it. Thanks! I think it will be useful to some!
Math & Science ⇒ siunitx Electronics Units
NEW: TikZ book now 40% off at Amazon.com for a short time.

siunitx Electronics Units
Did you check the manual of the siunitx package? On page 5, an example is given. The details are on page 8.
OS: Debian/GNU Linux; LaTeX System : TeXLive; Editor : Vim