Consider  a  system  of   three  charges  $\frac{q}{3},\frac{q}{3}and-\frac{2q}{3}$ placed  at  points  A ,B and  C  respectively ,as  shown in the figure  below .Take  O  to be  the centre  of  the  circle  of  radius  R  and  angle   CAB= ${60}^0$

The magnitude  of  the  force  between  the charges  at  points  C and B  is  $\frac{q^2}{54\pi {\epsilon }_0{R}^2}$

The  electric  field  at  point  O is $\frac{q}{8\pi {\epsilon }_{0}R}$  directed along the  negative  X –axis 

The  potential  energy  of  the system is zero

The potential  at  point  O is  $\frac{q^{ }}{12\pi {\epsilon }_0{R}^{ }}$