Which wattage rating is used for NMEA 2000 termination resistors?

• A. 1/2 W
• B. 1 W
• C. 2 W
• D. 1/4 W

Answer: (D)

Termination resistors on NMEA 2000 are used to match the bus impedance and prevent signal reflections, keeping the CAN network clean and reliable. Each end of the CAN segment has a 120-ohm termination resistor, and the power they dissipate is driven by the bus’s differential voltage, which is kept relatively small.

In typical NMEA 2000 operation, the differential voltage across a termination is about 2 volts at most. The power in each resistor is P = V^2 / R, so roughly 2^2 / 120 ≈ 0.033 W per terminator. With one terminator at each end, the total is about 0.066 W. That leaves a comfortable margin for a resistor rated at 1/4 watt. That rating is standard for CAN/NMEA 2000 terminations because it provides ample headroom without unnecessary bulk or cost. Higher ratings aren’t needed in normal operation, and a smaller rating wouldn’t be reliable long-term.