Fig. 1. Schematic diagram of NMEA-0183 interconnection
The recommended wire insulation colors are now starting to be used by manufacturers of VHF Marine Band radios and recreation-grade electronic chart plotters in their provision of a NMEA-0183 interface on loose conductors that are part of a multi-conductor cable. Typically the length of the cable with the NMEA-0183 signals is not very long, perhaps only one-foot, and if two devices have to be interconnected, their integral NMEA-0183 cables may not be long enough to reach each other. In that situation it would be useful to extend the NMEA-0183 cable from one of the devices to reach the other device. The problem with that solution is finding suitable two-pair shielded cable with the corret wire insulation colors.
The topic of finding an off-the-shelf cable that complies with the NMEA-0183 recommendation for wire insulation colors to identify the signals in a four-conductor cable has been mentioned before in several threads discussing NMEA-0183 interfaces, but this thread will concentrate on the wire insulation color, how it came to be chosen, and where to find suitable wire.
As mentioned in one of the other threads, long-time forum participant FNO sent me about a 12-foot length of (very nearly) appropriate cable that he uses in his professional work in industrial control networks. The cable is made by a German wire manufacturer. The sample I received was marked
- LAPP KABEL STUTTGART UNITRONIC® BUS LD 2 x 2 x 0.22 ROHS ART. 2170204
I interpret this as a cable made by a firm LAPP KABEL of Stuttgart, Germany, with the registered product name Unitronic, and having two pairs of two-conductors with wire cross section area 0.22 mm2, compliant with the Reduction of Hazardous Substances regulations, company part number or article number 2170204. And many thanks to Frank for sending this to me. I am very appreciative of his kindness.
On the manufacturer's website I found the cable specifications:
https://products.lappgroup.com/fileadmi ... 0203EN.pdf
The specifications do not mention the wire insulation colors explicitly, but instead refer to "Core identification code acc. to DIN 47100."
Searching for DIN 47100, I found that DIN 47100 (Deutsches Institut für Normung or in English “German Institute for Standardization” number 47100) is a wire insulation color code for identification of conductors in the telecommunications industry in use prior to November 1998, but afterward said to have been withdrawn without a replacement. (Cf. : https://en.wikipedia.org/wiki/DIN_47100 )
The standard identifies wire insulation colors to be used in sequence in multi-conductor cables. The first four conductors are to use these colors:
- First conductor = white
Second conductor = brown
Third conductor = green
Fourth conductor = yellow
These are, indeed, the wire insulation colors specified by NMEA.
Regarding the size of the conductors, in this particular cable they are specified by their cross-section area in millimeters. A cross section of 0.22-mm2 is equivalent to AWG-24. The outer diameter of the cable including the outer insulating jacket is slightly greater than 7-mm or 0.28-inches.
In its literature, LAPP KABEL describes the typical use of this cable:
- UNITRONIC® BUS LD
Flexible bus cable with PVC outer sheath, for use in different bus systems
For bus systems like e.g. Modbus, SUCOnet, Modulink, VariNet.
There is no mention of use in NMEA-0183, which is NOT a bus system but rather a serial point-to-point interface system.
Based on this cable, the first actual sample I have seen of a shielded two-pair twisted-pair cable with proper wire insulation colors that almost conforms to the NMEA-0183 recommendation--in the recommendation the pairs are supposed to be individually shielded--it appears that NMEA has chosen a standard for their interconnecting cables that is in reality and practicality IMPOSSIBLE to comply with. It is thus little wonder than I have never been able to find any off-the-shelf cable that can be easily purchased in small lengths at reasonable prices which complies with NMEA-0183. It is also further confusing that NMEA--primarily an American marine standards organization--instead of using common Electronics Industry of America (EIA) wire insulation color codes chose to use a German wire color standard and a standard which has not been in effect for about 20-years.
ANOTHER "KABEL"
Browsing the LAPP KABEL catalogue, I found another cable which is similar to their article 2170204 cable: article 2170261. (See the LAPP literature for details.) The product description:
LAPP KABEL wrote:UNITRONIC BUS CAN A is a data cable with UL and cUL approval, for CAN (Controller Area Network) fieldbus system according to ISO11898 as well as for high performance data networks with 120 Ohms nominal impedance. The second pair can be used for electrical power supply for the logical bus units.
Pair 1 is White/Brown and Pair 2 is Yellow/Green.
This is again interesting because the cable is for a bus network, but NMEA-0183 seems to have adopted these color schemes for a point-to-point wired serial data connection. This cable would be appropriate for NMEA-2000, a bus system with a single pair data bus and a second pair for network interface power. But for NMEA-2000, NMEA uses a different color coding, White/Blue (for data) and Red/Black (for power).
It is often mentioned that NMEA-2000 uses CANBus, but from what I can tell (from some research on-line) the ISO 11898 standard does NOT get around to such mundane topics are wire insulation color. There is an SAE (Society of Automotive Engineers) standard called J1919-11, "Physical Layer, 250 Kbps, Twisted Shielded Pair" that might specify wire color, but at $81 to get a copy, I won't be able to tell you what it says. By inference, I suspect it calls for the data pair to be Green/Yellow, based on a wire vendor advertising a single shielded pair cable with those conductors.