I'm still mystified. How do people treat
ground-and-negative power
differently from ground-and-positive that makes ground stabler?
If you have multiple power supplies of the same nominal voltage supplying
different parts of the system (say several 5V PSUs, each supply part of
the TTL logic in the device), you only interconnect one side of them,
conventiaolly the side that's called 'ground'. If you conenct both side,s
you're connecitng the PSUs in parallel and either high currents will
flow in an attempt to equalise the voltages, or one supply wil lend up
doing most of the work, since the 2 supplies won't have exactly the same
output votlage under all conditions.
In that case I cna think of times where it could make a difference
whether it was the positive of negative rail that was common throughout
the machine.
-tony