Moreover, a drop (also known as a spur) from an N2K backbone (aka trunk) can be much more than one cable to one device. Legal N2K network with 8 female ports and a 4-tee backbone That’s a big network, and I’m told that the NMEA was conservative in terms of what other standards permit on the same DeviceNet Micro C “physical layer” (also known as cabling and connectors). (And please ignore the wire nuts, which should never be seen on a boat.)īut for Micro cable networks the NMEA permits up to 50 devices on a backbone up to 100 meters (328 feet) long with numerous drop cables up to 6m (20ft) long (but not exceeding 78 m or 256 ft in total drop length). Secondarily, there can’t be much voltage drop as the 12v DC passes from the power drop cable out to the far ends of the network. The terminating resistors, for instance, are from different manufacturers (though they should provide the same resistance), and I think that skinny power drop cable may contain power wires even smaller gauge that the 22 AWG that’s normal with the N2K Micro size cabling most boats use.Īs I understand it, the main characteristic of a reliable N2K cabling and connector design is clean impedance in the data wires, which means good connectors throughout and proper backbone termination.
I don’t actually remember when or why I put together this funky 3-way backbone and power drop, but I know it works OK while also illustrating numerous poor practices. Funky DIY 3-way N2K network with backbone to growīut let’s start with what you can get away with… at least with a small NMEA 2000 network… and at least most of the time.
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