Re: Insulating D-shell from chassis?

I've been reading all the responses and decided to weigh in on the
matter. Assuming the db25 is computer parrallel port to driver logic
and associated circuitry. Isolating the db25 could be solving the
problem in more than one method. Cable shielding to be done properly
should only be grounded on one end and that could be the source of
the problem. If you simply break the shield on one end that could be
the solution. Ground currents if not fully analyzed can be a tricky
problem, thats the reason for opto isolators. Is the pc and
the power source for the cnc electronics plugged into the very same
110vac duplex. If not, try that. If you have a voltmeter,
measure the voltage between the pc db25 shell and the cnc db25 shell,
it should be indestinguishable from random noise. If there is a
solid voltage even if it's half a volt, theres an issue. Second
would be, is the negative output of the cnc dc power supply tied back
to the power courd ground wire to the duplex? This is where it gets
tricky with ground currents. The metal associated with any exposed
cabinetry should be connected to a safety ground, but not necessarily
the negative of the power supply. I don't have enough room to go
into all the details of which is correct because it's a total system
analysis and each unique application is different. But in very brief
terms if the pc and the cnc PS are plugged into two different 110
circuits and one has a device that for some reason is leaking a
current through its ground, that will raise a potential difference of
the duplex ground betwen the two circuits and you have a ground loop
via the ac wiring. The same is true for how the power to the
steppers and the drivers and associated logic is handled. Anytime
you get that potential and the negative of the power supply is wired
to ground--> a GROUND LOOP results.

Phil