be specified by the specific manufacturer of an
electronic device.” So, what arethe NMEA’s
general recommendations? I’ve adapted them
as follows:
- All metal-cased electronics equipment
shall have a case ground tied to the boat’s
DC grounding system with at least 12
AWG cable, but preferably 8 AWG. - All metal structures mounted to the ves-
sel, such as tuna towers, radar arches, and
outriggers, are required to be connected
to the boat’s DC grounding systems by at
least two conductors with a minimum
size of 6 AWG. Further, these grounding
links are required to be labeled “Ground
Connection, Do Not Disconnect.”
- Finally, the NMEA standard describes RF
grounding quite specifically as a common
ground used to reduce stray radio fre-
quency noise and “set” all cases of elec-
tronic equipment at ground potential,
free from noise sources that may be intro-
duced from being connected to the DC
or AC ground buses.
This last statement is where things may get
a bit confusing. The standard goes on: “The
grounding systems 127
Battery Charger Installation
power inlet (electrically
insulated from the boat
if isolator is installed)
shore
connection
shore-power
cable
main shore-power
disconnect
circuit breaker chargerbattery
DC grounding
conductor
AC grounding
conductor
main AC
two-pole, three-wire grounding bus
grounding-type
plugs and
receptacles
optional
galvanic
isolator
polarity
indicator
engine negative
terminal or its bus
battery battery
switch
to engine
cranking
motor
shore sideboat side
shore-power
cable connector
ungrounded conductor (black)grounded neutral conductor (white)grounding conductor (green)
L
N
Notice the differences between the ABYC standards for grounding in a battery charger installation per ABYC Standard
A-31 (shown here), and the more general installation standards for lightning, shock, and corrosion protection as stated
in Standard E-11 and shown in the previous illustration. If you study these diagrams carefully, you’ll notice that in the Stan-
dard E-11 drawing, each component connected to the grounding system has only one wire linking it to ground. No
loops are shown. But in the case of the Standard A-31 drawing, a loop is created between the AC and DC sides of the
grounding system (highlighted area). (Reprinted with permission from Boatowner’s Mechanical and Electrical Manual,
third edition, by Nigel Calder)