NMEA 2000 4 x T-pieces

NMEA 2000 is the marine version of the CAN networks found in every modern car. NMEA 2000 allows marine electronic devices from different manufacturers to talk to each other

NMEA 2000 is a standard set of data messages, protocols and connectors that all NMEA 2000 devices must use*

* Note –   Some manufacturers have created their own “flavours” of NMEA 2000 with different connectors and cabling; Raymarine’s “SeaTalkNG” and Simrad’s “SimNet” are two examples and both need proprietary adaptor cables to connect to standard NMEA 2000 networks.

You cannot just plug two NMEA 2000 devices together with a suitable NMEA 2000 cable – they must be connected to a properly constructed NMEA 2000 network.

Each device has an NMEA 2000 interface that must be powered from the network. Some smaller low power devices, like sensors are also powered from the network

There is a small cost in setting up the network, but future expansion is very easy. A Digital Yacht NMEA 2000 Starter Kit is a cost effective way to build a small, expandable network

Digital Yacht NMEA 2000 Starter kit includes:

• 4 way T-Piece Backbone
• 2x Terminators
• 1m Power Cable (fused)
• 1m Drop Cable

The part number is ZDIGN2KIT.

The list below, gives you all of the key NMEA 2000 networking rules that, if followed, will ensure your NMEA 2000 network works correctly.

1. The network must be properly terminated; only two terminators fitted one at each end of the backbone
2. The NMEA 2000 Supply voltage must be between 9V and 16V
3. The NMEA 2000 Supply current must be less than 3A (60 LEN)
4. Maximum number of 50 physical devices on the network
5. The NMEA 2000 backbone must be less than 100m
6. Maximum single drop cable length is 6m
7. Total length of all drop cables must be less than 76m
8. The volt drop from one end of the network to the other, must be less than 1.5V

A key consideration in any good NMEA 2000 network design, is the total current that the network is consuming. If the total current is more than the safe current capacity of the NMEA 2000 cabling (3A for all Digital Yacht cables) then the cable could melt or even cause an electrical fire.

• Each device on the NMEA 2000 network consumes some current
• It is very important that the total network current is known and that it is less than 3A
• Every NMEA 2000 certified device, has a Load Equivalency Number or “LEN” for short
• 1 LEN = 0.05A (50mA)
• The LEN number will be printed on the devices product label (see example below)
• Add up the LEN values of all devices and make sure the total is less than 60 LEN which equals 3A