Let me start by being very clear, old electric motors does not mean bad electric motors! Like in most things, there are plenty of good, older electric motors out there running in plants. Motors from the 1960's to 1980's that are running with very little maintenance requirements and little to no problems. On the flip side, every plant has bad actors that seem to require additional "love" from maintenance.
A question for the ages, Should you purchase a spare electric motor to have "on-hand" in the event your motor fails? A simple question but there is no clear answer out there. The reason for that is because it all depends on your situation, the type of motor, and the criticality of the driven machine.
There are not many new plants being built these days. Yes, there are some but most of what takes place today is retrofitting of older, existing equipment in plants that already exist. This process of retrofitting older equipment to new, modern, technology can be complex. We see many instances where someone replaces without considering all of the aspects of a replacement and the motor ends up not working. This article should serve as a guide for doing retrofits on large electric motors, focusing on AC Induction motors. We also want to give credit for a lot of this information from our friends at Siemens. They do many retrofits every year with us as well as their other channel partners.