Appendix C: Grounding and RF protection
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About marine grounding
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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
Definition
DC Negative
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.
Lightning
Ground
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.
Corrosion
System
Ground
Bonding arrangement that ensures equal electrical potential for all dissimilar
underwater metal parts and provides galvanic protection by means of
sacrificial anodes.
AC Ground
(Protective
Earth)
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.
RF Ground
(Capacitive)
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.
RF Ground
(Electrical)
Underwater ground potential that is electrically coupled to seawater ground
by means of a separate ground plate (e.g. Dynaplate). Also referred to as
“counterpoise” for the SSB/HF aerial system.
