Short Circuit (Series):

Within a DC circuit, the only current limit is the circuit resistance. If the resistance suddenly becomes zero and if there is no resistance in a circuit, an extremely large current will flow.  That condition of very low resistance and high current flow is called as a "short circuit" which was shown in the Figure.

Figure: Shorted DC Circuit

A short circuit is said to exist if the circuit resistance is so low in which current increases to a point where damage could occur to circuit parts. Along with an increase in circuit current flow, a terminal voltage of the energy source will decrease.  That occurs due to the internal resistance of the energy source causing an increased voltage drop inside the energy source.  An increased current flow resulting from a short circuit could damage power sources, burn insulation, and begins fires.  Fuses are given in circuits to protect against short circuits.