NEMA 2000 Wiring

Written by Todd S. Go2marine/LFS Tech Support

NEMA 2K is found on almost every boat now days in some way. Manufactures and electronics companies have integrated this system into almost every aspect of communication. I will discuss examples of where this may be found or utilized with a boats electrical system, along with some basic trouble shooting and repairs.

First I will break down the wiring side of the NEMA 2K. There will be 5 wires total contained in the Drop Cable , including a bare, red, black, white, and blue. The bare wire will be the shield wire, the shield wire shields the ground, signal, and power wires from any type of radio frequency interference. The red wire is used for a 12V positive power wire. You have what is called a NEMA starter kit which will include a NEMA Tee or instrument drop, that is where your 12V fused power comes in. Next the black wire is a 12V negative for power. The white and blue wires are signal wires, the white will be net-h and the blue will be net-L. The beginning and end of a NEMA 2k network has to be terminated with two 60 ohm resistors, one Female Terminator and one Male Terminator that total 120 ohms.

When building a new network, for example installing new electronics on an older boat, you will need to start with a NEMA Starter Kit. There will be one tee and one connecting wire per addition to the NEMA 2k network. For instance, if you have a radar, transducer, auto pilot, stereo, and a display you will have six tees counting your power wire tee. Keep in mind there is a cumulative maximum length cable that can be ran and it can be no more than 256 feet. Also no drop should be more than 20 feet.

Running NEMA 2k cable can be a pain with the bigger ends on the cable, the ends can be cut off to run the cable through tight spaces. There are field Male Serviceable Ends and Female Serviceable Ends available that can be installed once the cable is ran. These connectors must me soldered on due to them being signal wires, each strand of wire must contact each other at the connector for optimal performance. There is also a NEMA Bulkhead Adaptor for ease of instillation. Included below is a pin out diagram for NEMA 2K wiring.

When trouble shooting NEMA 2k wiring issues first thing to check is to make sure you have 12VDC coming through the backbone along with a good ground. If power is present, you can take your Digital Multimeter and put it on the ohm setting and ohm each wire to ground to see if it may be shorted to ground. After verifying all those tests, you can ohm out each wire individually to see if there are any breaks in the wire internally. On a non-broken wire, you should have a reading of around .5 ohms, and any more than that there will be broken or shorted wire. If you have a broken or shorted wire internally then that whole drop will need replaced.