To obtain a 60 Ohm meter reading between the blue and white NMEA 2000 data wires, power to the network must be OFF.

To obtain a 60 Ohm meter reading between the blue and white NMEA 2000 data wires, power to the network must be OFF.

• A. False
• B. True
• C. Not applicable
• D. Unknown

Answer: (B)

The data wires on an NMEA 2000 network form a CAN bus that is properly terminated with two 120-ohm resistors, one at each end. Those two terminators are connected across the two data conductors, so when you measure DC resistance between the blue and white wires with a meter, you’re effectively reading two 120-ohm resistors in parallel, which totals about 60 ohms. Power must be off because you’re trying to measure the passive termination network, not the active signaling circuitry inside the CAN transceivers. When the network is powered, the transceivers and biasing networks distort or overwhelm the DC resistance, giving a meaningless reading and potentially risking your meter. So a steady ~60-ohms indicates the bus is properly terminated with power removed. If the network is powered on, you won’t get a valid 60-ohm DC measurement.

The data wires on an NMEA 2000 network form a CAN bus that is properly terminated with two 120-ohm resistors, one at each end. Those two terminators are connected across the two data conductors, so when you measure DC resistance between the blue and white wires with a meter, you’re effectively reading two 120-ohm resistors in parallel, which totals about 60 ohms. Power must be off because you’re trying to measure the passive termination network, not the active signaling circuitry inside the CAN transceivers. When the network is powered, the transceivers and biasing networks distort or overwhelm the DC resistance, giving a meaningless reading and potentially risking your meter. So a steady ~60-ohms indicates the bus is properly terminated with power removed. If the network is powered on, you won’t get a valid 60-ohm DC measurement.