250-50 equipment grounding connections.the grounding connection for metal non current-carrying equipment shall be made on the supply side of the service disconnecting means or as outlined in section 250-5(d)if for a separately derived system.(1975 electric code)

250.50 Grounding Electrode system.All Grounding Electrodes as described in 250.52(a)(1)Through(a)(7)that are present at each building or structure served shall be bonded together to form the grounding electrodes exist,one or more of the grounding electrodes specified 250.52(a)(4)through(a)(8)shall be installed and used.

Exception.concrete-encased electrodes of existing buildings or structures shall be required shall be required to be part of the grounding electrode system where the steel reinforcing bars or rods are not accessible for use without disturbing the concrete.