In[]:=
potential[n_]:=Range[0,n]
In[]:=
a={2,1,1};​​b={3,2};​​c={1,1,1,1};
In[]:=
Tuples[potential/@a]​​Tuples[potential/@b]​​Tuples[potential/@c]
Out[]=
{{0,0,0},{0,0,1},{0,1,0},{0,1,1},{1,0,0},{1,0,1},{1,1,0},{1,1,1},{2,0,0},{2,0,1},{2,1,0},{2,1,1}}
Out[]=
{{0,0},{0,1},{0,2},{1,0},{1,1},{1,2},{2,0},{2,1},{2,2},{3,0},{3,1},{3,2}}
Out[]=
{{0,0,0,0},{0,0,0,1},{0,0,1,0},{0,0,1,1},{0,1,0,0},{0,1,0,1},{0,1,1,0},{0,1,1,1},{1,0,0,0},{1,0,0,1},{1,0,1,0},{1,0,1,1},{1,1,0,0},{1,1,0,1},{1,1,1,0},{1,1,1,1}}