Open Circuit (Series):

A circuit must have a "complete" path for current flow, which is, from the negative side to the positive side of a power source.  The series circuit has only one path for current to flow.   No current flows if this path is broken and the circuit becomes an open circuit that was show in the Figure.

Figure: Open Series Circuit

Circuits could be opened deliberately, like as through the use of a switch, or they might be opened through a defect, such as a broken wire or a burned-out resistor.

Because no current flows in an open series circuit and there are no voltage drops across the loads.  No power is consumed through the loads, and total power consumed through the circuit is zero.