About Marine Grounding - KVH Industries FleetBroadband FB250 Installation Manual

Appendix C: Grounding and RF protection
C.3 About marine grounding
There is great confusion about the different ground terms used when dealing
with marine electrical installations. The various terms are listed below for
reference.
Term
DC Negative
Lightning
Ground
Corrosion
System Ground
AC Ground
(Protective
Earth)
RF Ground
(Capacitive)
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Definition
Actually not a ground but a current-carrying conductor
which carries the same current that flows in the positive
conductor. The DC Negative may be electrically
connected to seawater (at one point only, via the engine
negative terminal though the shaft and the propeller) or
left completely floating.
Ground potential immersed in seawater. Provides a path
to ground lightning strike energy. Please note that this is
not a functional part of any other electrical system.
Bonding arrangement that ensures equal electrical
potential for all dissimilar underwater metal parts and
provides galvanic protection by means of sacrificial
anodes.
Ground potential immersed in seawater (typically the
hull for steel and aluminum vessels). Serves as safety
ground (protective earth) thus preventing shocks or
electrocution in the event of a fault situation.
Underwater ground potential that is capacitively coupled
to seawater ground. Typically numerous pieces of
bonded underwater metal parts such as keel (isolated),
water tank, engine block etc. will act as a capacitive RF
ground (that is; no DC connection to seawater). Often
referred to as "counterpoise" for the SSB/HF aerial
system.

About marine grounding