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NMEA2000 Basics

For newcomers to NMEA 2000 connections systems, it seems a logical assumption that if you have two devices with NMEA 2000 connections ports, then all you need is a correct length NMEA 2000 cable to join them. You will find out below that this is not the case.

NMEA stands for National Marine Electronics Association. The NMEA 2000 communications standard was developed in order to standardise messages and connectors used by marine electronic devices

Sometimes abbreviated to N2K or NMEA2k

 

What is a NMEA 2000 backbone?

 

A bidirectional connection loom that connects multiple devices together to form a  data sharing network. Made up of a series of T pieces, drop cables from the T Pieces to the devices, backbone cables between the T pieces, termination resistors at each end of the backbone and a fused power cable. These NMEA 2000 components plug together without the need for soldering. 

The network is powered, enabling low power devices such as sensors & instruments to use the network as their power supply.

NMEA 2000 is not brand specific, there may be slight differences in style or colour, e.g a Garmin t piece is grey and a Navico one is black. They use the same connectors and are interchangeable.

 

NMEA 2000 components

 

T piece (Pic and link to 230099) – male one end female the other with a female drop cable connection. these can be connected together or joined via a backbone cable. Devices are connected via drop cable to the bottom of the T piece.

BASIC NMEA 2000 RULES

 

  • Backbone must be powered by a fused 12v source
  • Either end of the backbone must be terminated 
  • Maximum backbone length 100m
  • Drop cables from T pieces to devices are limited to 6m (with the exception of wind vanes)
  • Sum of all the drop cables must be less than 78m

How to build a basic NMEA 2000 backbone 

 

Example: connecting an external GPS antenna to a Chart plotter

Equipment required

  • Chartplotter
  • GPS antenna
  • 3 x NMEA 2000 T pieces
  • 2 x NMEA 2000 drop cables
  • 1 x NMEA 2000 fused power cable
  • 2 x NMEA 2000 termination resistors

Link the three T pieces together and connect the drop cables from the T pieces to the chart plotter and antenna as in the diagram below. Connect the power fused power cable to the last t piece (please note that on a longer network the power cable should be at the midpoint of the network to avoid voltage drops at the ends of the network). Connect the male and female terminators to the ends of the backbone.

A BASIC NMEA2000 SYSTEM

NMEA 2000 Starter kits

 

If you are starting from scratch then a more convenient and affordable method of purchasing  the necessary NMEA 2000 components is by way of a NMEA 2000 starter kit. These kits contain the main components of a NMEA 2000 backbone.

What a NMEA 2000 backbone will not do

 

  • Power a device that has its own power cable e.g. A chartplotter
  • Share image data such as Radar, fishfinder or charts
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