Specifications

Powertap can handle large loads as long as no more than 8
amps is drawn through any single segment of the trunk line.
However, cable resistance may limit your application to less
than 8 amps.
3.3 Micro/Mid Power Connection
Like the Mini power connection, power is supplied to a Micro/
Mid trunk line via a Powertap, which is shown in Figure 5.
3.4 Micro/Mid Power Capability
Micro/Mid cable is rated to 4 amps but like Mini cable,
strategic placement of the power source could support higher
current. For example, 8 amps of power could be supplied to
the middle of the trunk where 4 amps is supplied to both
sides of the power tap. It can handle large loads as long as
no more than 4 amps is drawn through any single segment
of the trunk line. However, cable resistance may limit your
application to less than 4 amps
3.5 End-Powered Network
End-powered networks are typically seen on smaller vessels
with only a few NMEA 2000® devices. Figure 6 shows an
end-powered network.
3.6 Middle-Powered Network
A middle-powered network is typically found on larger
vessels and is any network where the power is connected
to the network at some location other than at the end. This
network consists of two legs, one leg extending in each
direction from the power insertion point. Figure 7 shows a
middle-powered network.
3.7 Maximum Power Supply Voltage Drop
The NMEA 2000® network is designed to work properly as
long as there is no more than a 1.5 volt difference in the
power supply voltage between any two devices on the
network. Therefore, you should perform an estimate of the
voltage drop across a network using the following equation:
Voltage Drop = 0.1 x Network Loads x Network Length x Cable Resistance/100
Where: Network Loads is sum of Load Equivalent Numbers (LEN)
for all devices (see device nameplate)
Network Length is in meters
Cable resistance is in ohms/100 meters
(see pages 1 and 9 specifications)
Power supply voltage drop estimates resulting in less
than 1.5 volts across the entire network require no further
analysis. Likewise, estimates ranging between 1.5 and 3.0
volts require no further analysis as long as a mid-powered
network is used. Occasionally, estimated power supply
voltage drops will occur outside these limits and will require
further consideration through detailed calculations by
certified technicians.
4. Ground the Network
The NMEA 2000® network should be grounded at ONE
Figure 6
End-Powered Network
72
TR TR
Depth Sounder
0.3 meter
2 loads
0.3 meter
2 loads
2 meters
1 load
Compass Display
0.3 meter
2 loads
Electronic Compass
2 meters
1 load
Speed Log
10
meters
2
meters
5
meters
.03 meter .03 meter
Autopilot
Power from
Battery
TR
Trunk Line
Drop Line
Device or Node
Drop Te e