Advanced Marine Electrics and Electronics Troubleshooting A Manual for Boatowners and Marine Technicians

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)