water accessing electrical panel

When it rains heavy I get water in the electrical panel which is located in the basement. The problem is when they wired the house originally they neglected to add a "drip loop" prior to the main line entering the box. There is plumbers putty at the meter outside the house which should keep the water out. If I add another wad of plumbers putty at the lowest point before the wire enters the box will this keep the water out in the future? Is it common to have a drip loop in the line before it enters the box? Thanks in advance.