Very often machines like compressors, pumps, and fans are driven by electrical motors and powered from the electrical grid. Some severe problems in the field can have a root cause in the grid itself or the connection of the machine to the grid. Due to this it is state of the art to monitor not only bearing or winding temperature of a machine but also under voltage, over voltage, phase asymmetry, or phase loss. There are some significant differences between those measurements performed in a lab and done in the field, especially if machines are used worldwide, and are connected to various grids. This paper presents some constraints which are important for those measurements.