Hello all,
I am currently dealing with a device which seems to have a bizarre earth issue.
The device is a piece of industrial equipment, it is being powered by a DIN rail Class-I AC/DC SMPS (TDK Lambda series) and operates on 24VDC from a 230VAC supply. The internal metal work of the equipment (which is bonded to the earth pin of the incomming power to the power supply) is sitting around 55VAC above ground (at 50Hz precisely so it's mains referred) when measured with a meter.
This is causing a 'nibble' to operators whenever the case is opened.
Probing the +/- output of the PSU shows there is negligible AC component, (around 70mVAC) as well as the + or - pins to ground, which again show negligible AC components. The DC cable run from the PSU to the equipment is short and I can't see how it could inductively pick up anything along the way. Essentially I've got a very noticeable 55VAC 'appearing' from nowhere inside the unit, there is nothing inside the equipment which could potentially generate this stray voltage (it's an instrument amplifier and a few solenoid valves).
Any tips for dealing with bizarre earth faults? I've not had a good chance to look at it yet, but it's a bit of headscratcher. If the DC lines contained a large AC component I'd understand, but this voltage appears from 'nowhere'.
Being an instrument amplifier, having a stray 55VAC in the unit isn't helping with accuracy either!
Any suggestions, could this be PSU related or is it being coupled in from somewhere else?