NMEA 2000 also specifies maximum allow-
able voltage drop as supplied by a battery at
1.5 V, and it goes into great detail explaining
step-by-step procedures for checking each leg of
the network as more nodes are added to the sys-
tem. Use the inTELLECT meter (see Chapter 2)
to determine if cabling is within the allowable
parameters. Concerns with voltage drop apply
to any network system, so always identify and
use specific manufacturers’ requirements. If you
really want to learn more about the intricate
detail of these systems, I strongly recommend
that you get a copy of the NMEA’s Installation
Standards for Marine Electronic Equipment Used
on Moderate-Sized Vessels, second edition. Go to
http://www.nmea.org to order a copy (it’s not free—it’s
$175 for NMEA members and $295 for non-
members—but it’s worth every penny).The Future of Onboard Power Distribution
Another area of onboard wiring that is rapidly
changing is power distribution to equipment
other than electronics. This applies to DC and,in some cases, AC power. Many companies
have entered the marketplace, some of them
with systems that have been used successfully in
the commercial aircraft industry for several
years. These same systems also use computer-
based protocols to send data, and as already
stated there are protocols in place other than
the NMEA 2000 standard. Some are CAN-
based networks just like NMEA 2000 and
SmartCraft systems, and others are not.
Three-Wire Power Distribution
The basic goal behind these new power distri-
bution systems is to dramatically reduce the
actual amount of wiring needed on board the
boat. The systems will still use the traditional
DC positive conductors and negative returns
to and from a main distribution panel. The
essential difference, though, is that these sys-
tems will use only one positive conductor and
one negative conductor to power multiple
DC loads distributed throughout the boat.
The third wire in the system will beused as a
two-way data communication cable that
will have multiple uses, such as actual data196 marine electronics installation and troubleshooting
Ohms/ Ohms/
AWG Feet/ohm 1,000 feet mm^2 Meters/ohm 1,000 meters
10 980.4 1.01 5.26 304.8 3.28
12 617.3 1.62 3.31 191.9 5.21
14 387.6 2.58 2.08 120.6 8.29
16 244.5 4.09 1.31 75.9 13.17
18 153.6 6.51 0.82 47.7 20.95
20 96.2 10.4 0.52 30.02 33.31
22 60.6 16.5 0.32 18.9 52.95
24 38.2 26.2 0.21 11.9 84.22
26 24.0 41.6 0.13 7.47 133.9
28 15.1 66.2 0.08 4.69 213.0Specifications are for copper wire at 77°F (25°C).TABLE Resistance for Copper Wire
17-1