Following a recent incident in which one of our people appears to have received an electric shock, we are trying to determine whether this was as a result of static or AC/DC volts. The person involved was working a fixed conveyor belt system used to transport plastic rolls to and from a mezzanine area. There is a history of static shocks from time to time but this particular incident appears to have occurred when the operative touched an uninsulated part of a light beam sensor. The machine was immediately taken out of use, electrically isolated, locked off until such time as it was checked out and the missing cover replaced by an engineer. Subsequent investigations have shown that the maximum possible volts from this were 15.2v AC and around 8v DC. My main question is as follows: Whilst this incident appears to have occurred as a result of the operative touching the uninsulated sensor, how could we determine whether a shock is as a result of static or AC/DC voltage? Thanks in advance for your input. Mike

MPH, The voltages you quote are unusual. Does this light beam sensor connect to a dedicated control? The uninsulated part, presumably is then conductive and metallic? Is this reliably earthed (not saying it has to be)? The better the earthing on conductive parts the higher the level of shock that will be felt due to the static charge, finding an easier path back to ground. It will be easy for a competent person to establish if the device is capable of delivering a shock, there are various tests that can be done checking earth paths, "fault loop impedances" etc. Some of the techniques would be more familiar to an install electrician, but not in the context of machinery, and there may be many machinery electricians that are not familiar with the concepts of testing for and proving automatic disconnection in the event of a fault. If the section of machine that was touched is reliably earthed, and correctly installed and connected then it will not be possible to experience an electric shock. Also you need to speak to the operative to find out what the shock felt like, if it was like a needle it will have been static, if it was more like a punch it will have been a.c. if they could not let go then it was probably d.c. A simple quick test would be to do an R2 test back to the local machine earth from the part of the sensor that "caused" the shock. An R2 test would be better understood by an install spark, but not in this context. Don't undertake an insulation resistance test on it though! ian, The fan was probably still earthed, which would be common practice, and thus it would have been a static discharge, remembering that in both your and the scenario described by MPH, it will be the person that is charged, not the equipment.