Re:Insulating D-shell from chassis

>I'm building chassis for my Xylotex controllers, and I need to
>insulate the female D connector from the chassis to prevent a ground loop in
>the signal path.

You should not have any electrical connection to the shell, including
ground. Any ground lines should run through a pin. The shell, if it is
metal, should be attached to the case with screws and spider washers to
ensure that it is at the same potential as the case.

If you suspect a ground loop, you can use a low amperage clamp on amp meter
and with everything running, check the ground wires for current
flow. There should be none. While on the subject of grounds, when you
are checking for building ground to machine ground, a good old fashion VOM
is a great tool, in fact much better than the digital ones. The digitals
tend to have a very high impedance on the input circuits, and can end up
not providing enough of a load to really check for ground/voltage potential
in a machine room environment. Back when we all got our new Fluke digitals
in the late 70's, and were checking out grounding on the new computer
instillations, we went nuts. We had weird voltages everywhere. We finally
had to go back to the old analog meters to get a good reading.

One other reason for my preference on an analog meter is that you can
detect very short pulses with it that the digital will never show. The
sampling time is just to long to catch everything.

Don