VFDs have been used to control the speed of electric motors for many years. However, many pump end users were hesitant to adopt this technology. Steps to increase efficiency reliability and the cost of VFDs have made this technology more approachable.Successfully including VFDs in a pumping system will involve an understanding of its operating principles and unique requirements. The first edition of this guidebook was one of the first non-commercial documents that provided information on these requirements relative to the pumping industry. This second edition adds a variety of additional details, covers changes in application and technology, and more thoroughly addresses troubleshooting. Changes made in the second edition include:• A new section on the maintenance of VFDs• Extensive rewrite of the application consideration for VFDs• Expanded section of VFD Input Power cables, motor cables, and controls• Expanded section on troubleshooting to include hardware issues and fault codes