Building an NMEA 2000 network can be a daunting task, with a number of standards and specifications that should be adhered to. We’ve outlined 3 fundamentals that highlight the importance of the NMEA 2000 specification.
1. Cable and connector types
NMEA 2000 utilizes the Device Net standard for cables and connectors. Using a universal standard makes things easier, simpler, and quicker. Because of this standard, we have the following options for cables:
NMEA 2000 cables
Lite or Micro Cables have a maximum backbone length of 100m, with a substantially high cable resistance. Whilst Mid and Heavy (Mini) cables can support up to 8 Amps thanks to the thicker wires and lower cable resistance. Be careful when using Mid Cable, as the current capacity changes greatly depending on the connector used.
Note how the max drop cable length does not change and is always 6m max. There is also another point to remember here, that the sum of all drop cables on a network should not exceed 78m.
2. Number of devices
The number of PHYSICAL devices (nodes) that can be on a network is 50, and the number of addresses available on that network is 252. You’d be right in thinking that doesn’t make sense, but remember that some devices can claim multiple source addresses (virtual devices).
Bridges can be used to overcome some of the network limitations; however, this makes for a more technical subject
3. Termination
Correctly terminating a network is something often forgotten about or missed. There should be a 120ohm ¼ watt terminator at either end of the backbone. These terminators are there to limit and prevent signal reflection which can cause data and communication issues on the network.
