3 Basics for Designing a Fault-Free NMEA 2000 Network

Building a NMEA 2000 network can be a difficult task, with a number of standards and specifications that should be followed. It's not as overwhelming as it looks, though, and as long as you follow the basics, you'll be off to a solid start. We have outlined three basics 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 may need.

1. Cable and connector types

NMEA 2000 uses the DeviceNet standard for cables and connectors. Using a universal standard makes things easier, simpler and faster. Due to this standard, we have the following options for cables:

The most important things to take away from this table are the spine lengths and current capacity. Lite or micro cables have a maximum backbone length of 100m, with a significantly high cable resistance. While 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 maximum cable length does not change and is always a maximum of 6m. There is also another point to remember here, that the sum of all the drop cables in a network should not exceed 78m. For smaller vessels and recreational boats this is not a major concern, but when building larger networks careful design and planning is required.

2. Number of units

Unit limits are also something that don't bother the recreational market nearly as much as the commercial market, but still they exist and should be followed.

The number of PHYSICAL devices (nodes) that can exist on a network is 50, and the number of addresses available on that network is 252. You'd be right to think 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 an 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 creates a more technical topic that will be covered in another article in the future.

3. Termination

Properly terminating a network is something that is often forgotten or missed. There should be a 120 ohm ¼ watt terminator at each end of the backbone. These terminators are there to limit and prevent signal reflection that can cause data and communication problems in the network. Sometimes installing a terminator on a sailboat can be a bit of a challenge as the spine has to run up the mast. These areas are limited in space, cumbersome and not always accessible. To overcome this, a terminator must still be used, but an inline terminator can replace the default "end of network" terminator.

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

Or download the Actisence guide to building a NMEA 2000 network as an e-book here.