In-Line Termination Resistors are typically used when:

• A. There are cable runs greater than 6 meters up a mast or tower.
• B. There is a single device on the bus.
• C. The bus uses fiber optic backbone.
• D. The device requires high data rate.

Answer: (A)

The main idea is to prevent signal reflections on a CAN-based network by properly terminating the line. NMEA 2000 uses a 120-ohm termination at the ends of the backbone to match the impedance and keep data edges clean. When you have long cable runs, especially up a mast or tower, the chance of reflections increases because the electrical length is greater and the end of the run may be physically distant or awkward to terminate exactly at the tip. Using an inline termination resistor helps ensure the line is correctly terminated along that extended run, maintaining signal integrity and reliable communication.

The other scenarios don’t address the need for electrical impedance matching along a long run: a single device on the bus doesn’t change the termination requirement, a fiber optic backbone changes the signaling medium and wouldn’t use electrical 120-ohm terminators, and data rate isn’t the factor—NMEA 2000 operates at a fixed CAN rate and termination is about preventing reflections, not speeding up data.