NMEA 2000 Cable Length and Device Limitations
When building your NMEA 2000® network, consider these limitations:
The distance between any two points on an NMEA 2000 network must not exceed 100 m (328 ft). To estimate this distance, measure between the terminators on your backbone and add the length of the drop cable for the devices connected to the T-connectors at the ends of the network.
The total length of all drop cables cannot exceed 78 m (256 ft).
The maximum length of a single drop cable from the top of a T-connector to NMEA 2000 device is 6 m (20 ft).
No more than 50 NMEA 2000 devices can be connected to an NMEA 2000 network.