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On occurrence of a short- circuit , the voltage at the fault point is reduce to zero and current of abnormally high magnitude flows through the network to the fault point.
On the other hand, an overload means that load greater than the designed value have been imposed on the system.
In case of an overload, the voltage at the overload point may become low, but can not be zero.
The undervoltage conditions may extend to some distance beyond the overload point in the remainder of the system.
In case of an overload, the currents are high but are substantially lower than in the case of a short- circuit.