In the good ol'(bad) maybe days. The CO's enforced an isolated ground
bond
network. Logic ground, or -48 return lines and chassis ground were separate.
The equipment chassis was bonded to the rack and the rack grounded but that
was, I believe for power cross protection. But today's equipment seems to tie
logic ground and chassis ground together for much digital equipment. (The
debate still rages between 1 ground and many grounds but I don't want to get
into that discussion for the moment.)This is a hard ground rather than a
capacitive or soft ground.
The -48 return line is tied to ground at the batteries - some distance
of
really large copper busbar away.
It would seem that the -48 return earth ground at the batteries and the
earth
ground of the chassis/rack can be some volts apart, and if the two were tied
together it would be problematic. I'm going to guess a 3 volts difference, not
because I know but because one of the RBOC's has a test for operation with a 3
volt potential.
What am I missing? (If its the boat let me down gently please, I'm old
and
sensitive)
Gary
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