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How do I check the health of my N2K cabling before powering my network?
Article Details

Last Updated:
Sep 12, 2011

Article ID:
443

Maretron recommends using an N2KMeter to diagnose the health of a network if you do not have an N2KMeter.

The pin assignments for NMEA 2000 are the following:

Pin 1: Shield (Bare)

Pin 2: NET_C (+12VDC, Red)

Pin 3: NET_S (Ground, Black)

Pin 4: NET_H (CAN High, White)

Pin 5: NET_L (CAN Low, Blue)

 

Please verify that:

 

1) All are secure on the NMEA2000 bus.

2) The bus has power (If you're using a yellow powertap, make sure that

+12V is supplied to both the brown and white wires, and that the blue,

gray,and black wires are all connected to ground.

3) The bus has two terminators attached.

 

Make the following measurements on the network to verify the integrity of the cabling.


Use a Maretron Field makable connector(FA-CM-ST) as shown in Figure 1.


 

NMEA2000 devices attached and teminators connected with power supplied to the network, please make sure that

1) You measure 12 VDC between pins 2 (Red) and 3 (Black) of all available open connectors .

 

Next, turn network power off on the NMEA 2000 network. Keep all devices disconnected, verify the following resistance measurements.

1) You should measure about 0 (short) ohms betweens pins 1 (Bare) and 3 (Black) of all connectors (This verifies that the shield is connected to ground). Demonstrated in Figure 2:


2) The shield should be grounded at one and only one point on the network. Disconnect that connection(at the powertap connection), and measure the resistance between pins 1 (Bare) and 3 (Black) of a network connector. This measurement should be very high resistance(OPEN). Reconnect the shield after this measurement is made.

3) You should measure about 60 ohms between pins 4 (White wire) and 5 (Blue wire) of all drop connectors (This verifies that both terminators are connected in the BUS. If you measurement is 120 ohms, then only one terminator is connected. If you measure a very high resistance, then no terminator is connected.

Demonstrated in Figure 3:



Remove both terminators from the NMEA2000 network.

4) Keep a single multimeter lead on pin 4 (CAN+/white wire),You should measure  0 (open)ohms between pins 4 (White wire) and any of the four conductors on the network cable. If you measure any resistance between pins 4 and other conductors, you have a short somewhere in the cabling.

5) Place a single lead on pin 5 (Blue wire) You should measure  0 (open)ohms between pins 5 (blue wire) and any of the four conductors on the network cable. If you measure a any resistance between pins 4 of any two connectors, check the cabling in between for a possible break.

 

If all of these measurements are ok, now we should check for any short circuits on power S . All of the following measurements should be very high resistance. If one of these is a low resistance, check for a possible short cable.

1) Pin 1 and 2

2) Pin 1 and 4

3) Pin 1 and 5

4) Pin 2 and 4

5) Pin 2 and 5

 


 

Ensure that:

1)  The two terminators are installed at the each end of the “trunk” of the network.

2)  A node has a drop from the trunk of more than 6 meters

3)  The sum of the length of all drops is less than 78 meters.

 

If you have gone through all of these steps free from issue, try adding components one by one to the NMEA2000 network to bring the network up slowly.

(NOTE: there must always be at least two components in a NMEA 2000 network (or any CAN network) in order for data communication to take place.

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