NMEA 2000 network diagram with NGX

The NGX-1 will be replacing the NGT-1 and NGW-1 soon.

Building an NMEA 2000 network can be a daunting task, with a number of standards and specifications that should be adhered to. However, it’s not as overwhelming as it looks, and as long as you follow the fundamentals, you’ll be off to a solid start. We’ve outlined 3 fundamentals that highlight the importance of the NMEA 2000 specification, and why these are required to ensure the network runs smoothly and displays the data you might require.

1. Cable and connector types

NMEA 2000 utilises the DeviceNet 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

The key things to take away from this table are the backbone lengths and current capacity. 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. For smaller vessels and leisure craft, this isn’t too much of a concern, but when building larger networks, careful design and planning are needed.

2. Number of devices

Device limits are also something which does not trouble the leisure market anywhere near as much as the commercial market, but nonetheless, they exist and should be followed.

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). For example, our W2K-1 NMEA 2000 Wi-Fi Gateway claims one address on the ‘physical’ product, and then one for each enabled data server. This results in up to 4 source addresses being claimed.

Bridges can be used to overcome some of the network limitations; however, this makes for a more technical subject which will be covered in a different article in the future.

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. Sometimes the installation of a terminator on a sailing boat can be a bit of a challenge as the backbone has to run up the mast. These areas are limited in space, awkward and not always reachable. To overcome this, a terminator must still be used, but an inline terminator can replace the standard ‘end of network’ terminator.

For more on building and testing your NMEA 2000 network, read our article here.

Or download our guide to building an NMEA 2000 network as an eBook here.