: When electricity flows through a conductor in a corner, it is more or less obstructed by the conductor. This barrier is called the resistance of the conductor. Resistance reduces voltage drop and current in the circuit. This is why resistance has to be adjusted sometimes in series, sometimes in parallel and sometimes in series-parallel. This combination of resistance is called resistance grouping. There are three main types of resistance grouping. Namely: (a) series grouping , ( b) parallel grouping and (c) mixed grouping.