THE ISSUE of vibration caused by line voltage unbalances is well documented and widely accepted [6]. The objective here is to quantify and expand on the net effect of these unbalances. An issue commonly encountered is that the ideal situation is typically not present, so the question becomes determining what is acceptable and what tradeoffs will be required to meet a given performance expectation. Within this discussion, there will be opportunities to have several conversations that may be illuminating. Motor vibration is a field of study that is at the same time both basic as well as complicated and nuanced. Analyzing a motor with vibration issues is often a process of elimination of “suspects” to arrive at the culprit. One of the usual suspects that flies under the radar is voltage unbalance. in the motor becomes unbalanced as well. Both of these effects have negative consequences and this paper will touch on some of these concerns and concentrate on one, vibration. The reasons for concern are as varied as the applications in which electric motors are used. The seriousness of one issue or another varies depending on the end user’s policies, practices, and the needs and expectations of each site. Unbalanced voltages can lead to several issues that we will discuss in brief, but have been discussed at length in other papers [1]–[۳]. Issues that have been found are higher temperatures, lower efficiencies, and higher vibration to name a few examples. This paper will concentrate on the effects of unbalanced voltage on the vibration of motors. The various effects of unbalanced voltage have negative consequences for motor operation and lifespan. In order to obtain a longer lifespan, end users and industry organizations have taken steps to provide guidance and requirements for motors. Commonly used industry specification such as IEEE 841 and the API 541, API 546, and API 547 standards have been established in order to have a consistent standard for construction and design of motors. Many aspects of motor performance that have a direct effect on the life of motors have been considered and guidance is offered in these specifications. One potential issue that may occur from operation on unbalance voltage is higher temperatures which stress the insulation system and shorten winding lives dramatically.