Section 125.21 - Grounding of Overhead Transmission Lines(1)Scope. 220 CMR 125.21 shall apply to the grounding of transmission line structures and equipment where the grounding is intended to be a permanent and effective protective measure.(2)Parts to Be Grounded. All metal conduits, cable sheaths, switch operating handles and metallic structures shall be effectively grounded.(3)Material and Continuity. In all cases the grounding conductor shall be of a metal or combination of metals which will not corrode excessively under the existing conditions and, if practicable, shall be without joint or splice. If joints are necessary, they shall be so made as to not materially increase the resistance of the grounding conductor.(4)Size and Capacity. The grounding conductor or conductors shall have a current-carrying capacity sufficient to insure continuity and continued effectiveness of the ground connection under and subsequent to conditions of excess current caused by either of the following: (a) Impulse surge due to direct lightning stroke to structure or lightning protection wires.(b) Power frequency follow current due to insulation flashover for the length of time required for the protective devices to clear the circuit. The minimum breaking strength of the grounding conductor shall be 1,000 lb.
(5)Underground Grounding Conductors. Wires used for grounding conductors, if laid underground, shall, unless otherwise mechanically protected, be laid so as to prevent their being readily broken. Joints shall be so made as to not materially increase the resistance of the grounding conductor.(6)Ground to Railway Returns. Protective grounds shall not be made to railway negative-return circuits.(7)Made Electrode Grounds. Where made electrodes are used, they shall, as far as practicable, be embedded below permanent moisture level. Made electrodes shall be of materials or combination of materials which shall not corrode excessively under the existing conditions. Made electrodes may be buried plates, ground rods, counterpoise, pole plates or wire attached to the pole before pole setting. Where conditions require more than one electrode, a single grounding conductor may be connected to a group of electrodes which have been bonded together for the purpose of lowering the resistance to ground of the group. No portion of a made electrode shall be installed with less than seven feet separation from underground pipelines.