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

record of satisfactory performance, do not
immediately assume the networked equip-
ment is at fault. The first step is to determine
if the more vulnerable wired connections are
faulty. If you have a new installation, the prob-
lem may be software incompatibilities or
glitches in the software itself. (Whenever I see
that a piece of gear is running or controlled by
version 1.0 of any software, I’m always suspi-
cious. The programming people don’t always
get things perfect on the first go-round.) If
you suspect a software problem, call the equip-
ment dealer or manufacturer to find out if
there is a history of problems, and what the
software solution might be.
The next step is to positively identify the
function of each of the networking cables
connected to the electronic equipment, and

then determine the function of each of the

pin connections in the cable assembly. You’ll

need to refer to the equipment owner’s man-

ual or installation guide for this information.

If you don’t have the documentation, you

might as well stop. You must know what role

each and every wire and pin play in the system

to determine if all the “dots” are connected

properly and that the cable harness is in good

working order.

The NMEA installation standard clearly

identifies standard color codes for its 2000

standard cable harnesses. These colors apply to

the individual conductors within the multi-

conductor cable. Due to the cable design,

however, you won’t really be able to see the

various colors; you are going to have to work

from pin to pin at the cable ends to confirm

proper continuity of conductors.

Remember that failures at the connection

point on the equipment are not uncommon,

and with a visual inspection you’ll be able to

see corrosion or loose wires. Slight corrosion

has a much more profound effect on a network

system’s ability to distribute data than on more

traditional electrical connections, so carefully

inspect the cables and connections. Look for

any signs of corrosion on the pins or socket

ends of the termination points. If you see

loose wires at screw and ring-eye connections,

tighten them.

If you use an ohmmeter for these tests,

take into account the inherent resistance of the

wire, which is very small gauge, typically 16 to

24 AWG (1 to 0.2 mm^2 ). The NMEA 2000

standard identifies maximum allowable resist-

ance values for power runs as 1.34 ohms per

100 meters for heavy-gauge network cable (16

to 18 AWG) and 5.4 ohms per 100 meters for

light-gauge network cable (22 to 24 AWG).

Table 17-1 identifies typical resistance values

for commonly used copper wire gauges as well

as the metric equivalents.

onboard networks 195

An NMEA 2000 network can distribute up to 1 amp per
device over network wiring. Beyond that, dedicated
power leads are required.

power

supply

connection

depth meter wind meter

radar unit

dedicated

power lead

for devices

+ VDC

ground

shield

drop cable

without power

connection

(provided by

manufacturer)