I remember seeing the mu symbol about fifty years ago when I worked with various relays. I believe that it denotes “micro disconnection” which is measure of insulation regarding the isolation across the contact(s). It gives the user confidence in the safety of the device and manufacturers often confirm the measure by stating a maximum voltage across the contacts before breakdown of the gap, such as 750V. I don’t imagine anything has changed over the years.
Last Edit: May 2, 2022 13:54:59 GMT 1 by lurcher: Stupid idea