Where air or water pipes parallel the grounded return of power circuits, the return shall be securely bonded to the pipes at frequent intervals to eliminate the possibility of a difference of voltage between rails and pipes and to prevent electrolysis of the pipes. The rail return shall be of sufficient capacity for the current used, independent of the capacity of the pipes. On main haulage roads, both rails shall be bonded, except welded track, and cross bonds shall be placed at points not to exceed 200 feet apart. On secondary haulage roads, one rail shall be bonded continuously.