How the use the guide. Understand how the motor is to be operated before selecting options below. A Variable Frequency Drive is also called a VFD. The variable frequency drive specification guide will generate a sample VFD specification in the field at the bottom, as well as indicate the selections you have made. If the variable speed ac motor application is understood, the guide should generate a sample specification that can save you valuable time. Use the VFD specification guide as a reference only, for example, during preliminary engineering of a project.