What is alternating current (AC)? This website provides explanations supported by illustrations. Check it out.
AC - Alternating Current Current that regularly reverses the direction of its flow in a repeating, cyclical pattern. AC is the dominant form of power because it can be transformed and transported over long distances.
"There is one very important point to remember when reading this article; It is the alternator, not the battery, which provides the requisite electrical power to operate the various, on-board devices." from the site
"An inverter changes 12-volt DC from your batteries to 120-volt (or 115 or 110) alternating current, the same as household power. It can run anything, from a computer to a freezer to an electric drill; and if sized correctly, it can run them all at once."(from Johnson's article)
Alternating current does change direction-- standard household electricity is alternating current, because of its flexibility in traveling long distances. It changes direction at a specific frequency-- 60 times per second, or 60 Hz (in the United States, Japan, and a couple of other countries; in Europe the standard is 50 Hz). (from the site)
"The ground-fault circuit interrupter, or GFCI, is a fast-acting circuit breaker designed to shut off electric power in the event of a ground-fault within as little as 1/40 of a second." (from the site)
ELCIs, and the more familiar GFCIs, are part of a larger family of devices that measure current flow in the hot and neutral wires and immediately switch the electricity off if an imbalance of current flow is detected. (from the site)