is concerned, or how much inherent noise the
device may be generating due to design fac-
tors. Therefore, it’s best to follow accepted
industry standards and specific manufacturer
recommendations for electronics installations.
ABYC Standard E-11, AC & DC Electrical
Systems on Boats, addresses grounding issues, as
does NMEA’s equipment installation standard.
From the ABYC’s perspective, case grounding of
equipment is one of the most important consid-
erations for a trouble-free installation. Another
is the single-point connection between the DC
and AC grounding systems on the boat. The
ABYC standards for grounding are summa-
rized in the illustration on page 126, which
I frequently rely upon for training purposes.
Keep in mind that this diagram reflects
grounding needs as they apply to lightning pro-
tection, shock hazard protection, and corrosion
protectionmore than to radio/electronic equip-
ment needs and the elimination of electroni-
cally induced “noise” (although a radio ground
plate is shown). Compare it closely to the
illustration on page 127 from ABYC Standard
A-31, Battery Chargers and Inverters, and
notice what is in effect a ground loop between
the AC and DC sides of the battery charger.
The grounding wire on the DC side of the
battery charger circuit may seem redundant,
but in the event of a case short with the DC
positive conductor, it is vital for providing a
conductor capable of carrying high current
back to the power source to ensure that the
fuse or circuit breaker in the DC positive line
will trip. In many cases, without this compara-
tively large conductor, the current would tend
to flow down the AC grounding conductor. In
all probability, this small conductor will not
have sufficient amperage-handling capabilities,
so it will overheat and possibly cause a fire.
The reason the ABYC standards don’t get
too concerned over this loop is based on the
premise that the DC grounding conductor is
not normally carrying any current; it’s merely
in place in case the worst happens. This raises
an important point about ground loops, how-
ever: they are never a problem unless electrical
current is flowing through them. But from the
troubleshooter’s point of view, that isthe prob-
lem, because the current needed to make elec-
tronic noise can be minute—too small to
pose a safety problem, but large enough to
affect the performance of some electronic
equipment.
The NMEA standards are a bit stricter in
some cases, and less strict in others. For exam-
ple, ABYC E-11 states that grounding con-
ductors can be no smaller than one wire gauge
size smaller than the DC power feed conduc-
tor to the device in question, and in no case
smaller than 16 AWG (1 mm^2 ) in size. With
AC equipment, the conductors are typically
the same size, as the power feeds to AC devices
are virtually always installed with triplex cable
with equally sized conductors sheathed in the
outer jacket. In contrast, NMEA recommends
using no smaller than 12 AWG (3 mm^2 ) in
any case for grounding purposes and prefers
the use of 8 AWG (8 mm^2 ).
The intent of the NMEA grounding stan-
dard is also telling, and reinforces the differ-
ence between ABYC and NMEA interests. To
quote from the NMEA standard: “This sec-
tion details the recommended standards and
practices for installation of grounding systems
intended to support electronic equipment on
vessels.” The NMEA is particularly focused on
the proper operation of electronic equipment
in a general sense. The ABYC, in contrast, is
only interested in the proper operation of
equipment if its faulty operation could cause a
safety hazard to people on board the boat. It’s
also important to keep in mindthe note that
follows the above statement from the NMEA
standard: “These are general recommendations.
Specific and more stringent requirements maygrounding systems 125