My house initially had many outlets grounded to the copper plumbing using ground pipe clamps like this one which I know are no longer allowed via code:
I have gone through and replaced my copper lines with PEX for finishing a basement. In the process I had an electrician install a new breaker box. The breaker box itself has a copper line that runs from it to my water supply source (copper line).
To avoid having to run new 14/3 wire for all outlets, is it acceptable to attach my outlet grounds to the circuit breaker ground wire using a split bolt connector like the one shown below? If it is acceptable, is there any guideline to how many per terminal are allowed?