Ground loops can cause System Damage

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Title: Ground loops can cause System Damage
Keywords: Ground loops, Opto-Isolated, damage
Author: MHH
Date: may 29 1995
KDB: kdb-105
Distribution: External

Preamble:
"A ground loop is a current through a conductor between
two two grounded points" as in two buildings connected by
an rs232/rs485 data line.

The potentials are different and if the voltage is great
enough ... a current flows down the signal ground of the
data cable ... and your serial port is damaged.

When two devices carry a difference in ground potential,
the potential will try to even itself out ... in much the
same way as water seeks its own level. It will travel
through the the lines and connectors and overload the
circuitry of both the high-potential and low-potential
device.

** A lightning strike or electrical spike ... is a sudden
event causing damage ... smoking chip/traces.

*** A ground loop is more insidious ... and is a long term
steady event that weakens the chip ... and slow cooks the
chips and they eventual fail ... blackened tops and melted
circuit boards.

Note:
A surge protector does NOT guard against ground loops.

The best prevention for ground-loop problems is to use
optical isolation on long data lines.