General Recognition shall be given to four essential points which characterize structures for outdoor substations. 1. Accuracy and Permanence??Structures shall be accurately fabricated to facilitate erec?tion. Specific consideration shall be given to prevent damage to protective coatings required by certain materials. 2. Rigidity??Consideration shall be given to providing sufficient rigidity so that all equip?ment@ such as air switches@ interrupter switches@ and circuit interrupting devices@ will operate properly and so that deflection of members will not be excessive or exceed the limits specified by the equipment man-ufacturer. 3. Erection??Outdoor substations are frequently erected by persons with varied' levels of ex?perience as structural erectors. This calls for great detail and clearness in drawings@ ac?curacy in fabrications@ and care in marking the structural components. 4. Design??Frequently it is necessary to deviate from conventional practices in structural design in order to provide electrical and mechanical clearances or to prevent inter?ference with switch operating mechanisms. Authorized Engineering Information 1-17-1968.