The information in this design guide is applicable to both rigid bus and strain bus designs for outdoor and indoor@ air-insulated@ alternating current substations. Ampacity@ radio influence@ vibration@ and electromechanical forces resulting from gravity@ wind@ fault current@ and thermal expansion are considered. Design criteria for conductor and insulator strength calculations are included. This guide does not consider the following: a) The electrical criteria for the selection of insulators (see IEEE Std 1313.2TM-1999 [B22]) b) The seismic forces to which the substation may be subjected (see IEEE Std 693TM-2005 and IEEE Std 1527TM-2006) c) The design of mounting structures d) Design considerations for contaminated environments (see IEEE Std 1313.2-1999 [B22]) e) Installation methods f) Design of direct current buses Purpose Substation rigid and strain bus structure design involves electrical@ mechanical@ and structural considerations. It is the purpose of this guide to integrate these considerations into one document. Special considerations are given to fault current force calculations. The factors considered include the decrement of the fault current@ the flexibility of supports@ and the natural frequency of the bus. These factors are mentioned in ANSI C37.32-1996 but are not taken into consideration in the equations presented in that standard@ including intended users and benefits to users.