What cable specification should I use for my NMEA 0183 product?
Most Marine Data products use ‘NMEA 0183’ compliant data transmission. This transmission is based on the RS422 standard and operates with a data rate (baud rate) of between 4800 bits per second, and 38400 bits per second (depending on the data source)
Ideally ‘Twisted Pair’ cables should be used for the data transmission, and according to the RS422 standard, cable lengths of up to 1500 meters are possible for the data rates used for this equipment
For cable lengths much shorter than 1500m, twisted pair cables are not necessary. For this reason, the supplied 2.5m cables on the majority of equipment do not use twisted pairs.
We recommend using twisted pair cables for the NMEA 0183 data for lengths over 20m at 38400 baud, or over 50m at 4800 baud.
For the NMEA 0183 (RS422) data, a cable section of 0.25mm2 is suitable (the data signal current is only ~2mA).
Likewise, for short cables, a cable section of 0.25mm2 is suitable for the power supply connection to most of our NMEA 0183 products. However for longer cable runs, a larger section may be advisable (DC supply current at 24VDC <=120mA)
For the DC supply conductors, the resistance of each core of the cable should ideally be no more than 2 ohms, (although resistance of up to 10 ohms per conductor should cause no problem).
From the formula L=(R*CSA)/0.017 (for copper wire. R = resistance, CSA = section in mm2, L = Length in meters) (2*0.25)/0.017 = 29m is can be calculated that a 0.25mm2 would be OK for up to 30m.
If an external remote dimmer is not used in the setup, only 4 cores (2x Twisted Pair) are necessary (+24VDC supply, 24VDC Supply Return, Data A, Data B)
If the external 0-24V Dimmer signal is to be used, 6 cores (3 pairs) will be necessary).
Please see equipment user manuals for conductor connection details.
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