Alternating current (AC) and Direct current (DC) are the two basic types of electrical sources. Direct current flows in only one direction whereas Alternating current continuously reverses direction.

In an AC or DC circuit, a complete path is required in order for current to flow through the circuit. When a complete circuit path or closed circuit exists, the circuit conductors and the load form a loop, and the load creates resistance in the circuit which will limit the overall amount of current flow.

An open circuit occurs when a switch or other form of disconnection device located in the loop is opened thus making the circuit path incomplete.

A short circuit occurs when the conductors in the loop somehow become connected together. For example, if an insulation failure between two or more ungrounded conductors of different polarity created continuity between the ungrounded conductors, a short circuit condition would occur.