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 MIL-HDBK-419A
5.4.1 Lower Frequency Network (0-30 kHz, and in some cases up to 300 kHz). The lower frequency grounding
network for the facility should conform to the following principles:
a.
It should be isolated from other ground networks including structural, safety, lightning and power
grounds, etc. The purpose of this isolation is to prevent stray currents (primarily 50/60 Hz power) from
developing voltage differentials between points on the ground network.
b . The inter-equipment or facility ground system should not be expected to provide the primary return
path for signal currents from the load to the source. Figure 5-18 illustrates a way of discriminating against
those extraneous signals which may inductively or capacitively induce currents into the grounding network and
develop differential voltages between the source and the load. For example, Figure 5-19 illustrates a practice
that is not recommended. If only one source and one load constitute the entire system or if the various
source-load pairs within the system are essentially noninterfering in nature of their operation, this grounding
arrangement may be acceptable.
c . The lower frequency grounding network must be connected to the earth electrode subsystem at only
one point.
Figure 5-18. Recommended Signal Coupling Practice for Lower Frequency Equipment
5-29
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