NMEA-2000 Micro Connectors

[jimh]

The most commonly used pre-made wiring for NMEA-2000 network installation on small boats uses the DeviceNET Micro connector. Information about the arrangement of the pins and sockets on these connectors and the color code of the wiring usually used in the connected cables is given graphically below. These drawings show the pin arrangement when viewed by looking at the mating face of the connector from its front.


NMEA-2000 Micro connector socket arrangement


NMEA-2000 Micro connector pin arrangement

To aid in interpreting the wire color of the signals, think of the data pair as white-hot and blue-cold. Power circuit polarity is with the usual red-positive and black-negative.

I made these drawings myself because all the drawings I could find for these connectors were flawed. These other drawings showed the connector keyway oriented in odd positions, or used odd and non-intuitive names for the signals (although they might have been the official names), or used the same representation for both pins and sockets, or did not always show the wire colors associated with the circuits. My drawings show the keyway in the usual topmost rotation, use signal names in understandable nomenclature, include the wire colors, present the pins differently than the sockets, and avoid using the gender designators of male or female (because those designators often apply to the connector body and not the electrical contacts and cause confusion).

These connectors are often referred to as "Micro-C" connectors. That usage is probably a contraction of the trade name Micro-Change® used by the OEM MOLEX for their line of connectors used in NMEA-2000 applications. Micro-Change may also be a contraction of Brad®Micro-Change®. I also found other uses of "Brad" associated with connectors of this general type, including a branding of them as Brad Harrison®Micro-Change®

I also found that connectors like these sold under those more industrial-market trade names are typically at least twice as expensive as compared to very similar cables and connectors being sold in the recreational marine market, and I don't recommend looking for any bargains among those industrial-market suppliers or vendors. But for the curious, here is a link to the MOLEX catalogue page on their versions:

https://www.molex.com/en-us/products/in ... change-m12

[jimh]

My interest in the contact arrangement in the DeviceNET Micro connector was sparked by an inquiry regarding how certain pre-made cords intended to be used to provide a power-node on the network backbone were wired. I offer some observations on that topic as a corollary topic to the connectors themselves.

NMEA-2000 Power Node Wiring
The usual NMEA-2000 practice is for the power-node cable to provide three conductors on the wiring end of the cable, as follows:

--RED for the network power positive
--BLACK for the network power common, and
--BARE for the network shield or RF GROUND

The pre-made cables from NAVICO for use as power-node cables only provide two conductors, the RED and BLACK. Using a continuity checker, I found those NAVICO power-node cables contain an internal connection between circuit 1 SHIELD and circuit 3 -V or power common. This is a reasonable provision for using the power-node cable on a fiberglass boat where it is very unlikely there is any sort of separate RF GROUND circuit, and where one usually finds the battery negative is tied to the outboard engine chassis. Connecting the power common to the shield in the pre-made cable is then acceptable practice under the NMEA-2000 installation guidelines, which caution that there should only be ONE connection between shield and the boat's ground in the network. That connection then occurs in the pre-made power-node cable where the shield is bonded to power common.

Other vendors of NMEA pre-made power-node cables do provide the third wire for RF GROUND in their wiring fan out, allowing the installer to determine where best to connect that conductor.

A source of trusted advice on NMEA installation practices is from a presentation made by NMEA at an IBEX session. The presentation is memorialized in the Power-point file on the NMEA website. You can obtain this from

http://www.nmea.org/Assets/2012%20ibex% ... lation.pdf

In the illustration on the page (41 of 82) titled "Power Insertion" there are notes that advise, "Shield/Drain wire connects to RF ground at one Power Point Only" and "Shield/Drain left unconnected at all other insertion points."

[jimh]

The diameter of a typical DeviceNET MIcro C cable as sold by an OEM manufacturer (MOLEX) is shown in a drawing at

https://www.molex.com/content/dam/molex ... 978_sd.pdf

The "coupling nut" outside diameter is 14.5-mm.