cor.vandewa...@gmail.com said:
You do not really have a ground fault, it seems your power supplies have an input circuit that causes a small current to ground
John, are these built as DC/DC converters? Or are the AC-input power supplies that you are using with a DC input?
AC power supplies usually have noise filter caps, and resistors to discharge these capacitors when unplugged to satisfy UL requirements. It's common to find capacitors from hot and neutral to ground, and a high-value resistor or two to ground to discharge them.
If the supply has no ground pin (2-wire cord or wall-wart), then there will be a capacitor and resistor from the AC input side to the output side, in the hopes that the output negative side "might" be grounded. If this is the case, you could remove these capacitors or resistors to cure your ground fault.
UL requires a considerable amount of insulation between AC and DC sides (like 3750vac for one minute with less than 1ma leakage). But there are tons of cheap supplies that simply don't meet the standard. They either ignore UL, or lie and put a fake UL label on it.
Some small AC switchmode supplies I've taken apart have gone so far as to wind the primary and secondary of their transformers with ordinary magnet wire, one directly on top of the other, with no supplemental insulation at all! That gives them a breakdown voltage barely over AC line voltage -- no safety margin at all. A voltage spike, age, or moisture can puncture this insulation, and the supply will probably work anyway -- but with a path from input to output.
Similarly, some DC/DC converters have only a small amount of isolation between input and output. It's not required for many applications, where input and output both share a common ground anyway. Such supplies can be UL listed with only 500v isolation between input and output (and it's a 1-time, 1-second test; not 1-minute with repeated tests allowed as for AC).
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