Electronics with Pos, Neg and Drain wires

[Ward H]

I'm ready to run power connections to a chart plotter, SeaTalkng network and ACU for an auto pilot.
All three need a positive, negative and "rf drain" connection. Manuals state if the boat does not have a separate RF drain connection to connect the RF drain to the battery negative connection.

Two of the devices have power cables I need to extend. One device needs a power cable.

Do I need something like 14-3 to make these connections? The only 14-3 I've found is listed as AC cable. Maybe because the wire colors are black, white and green.

Thanks
Ward

 

[Ron20324]

Uummm... I believe you can connect the drain to the neg at the device and just run a 2-wire. I'm not sure where you would connect a drain to otherwise. I'm sure "Sparky" has a better answer?

 

[Ward H]

That sure would simplify things.

 

[LeslieTroyer]

That is what I’ve done.

 

[uncledom]

Ward if you have a cable with a true drain wire in, such that it is wrapped on the inside like a shield, make sure you only ground one end or you could induce noise on the cable.

 

[Bill Roosa]

SeaTalk (NEMA 2000) supplies power to all the units from the network cabling so not sure what devices you would be powering AND connecting to the network.
This is an electrical noise shilding issue not really an RF noise being produced by the cables one. Just grounding it with a small diameter wire (14 gage would be massive overkill IMHO) will be sufficient to protect the cables inside the network cabling from RF interference.

 

[LeslieTroyer]

Lots of devices are connected to the the network AND external power, VHF, AIS Xmit, Auto Pilots, Chart Plotters all can pull more than the network can supply so they have external power.

 

[Ward H]

@LeslieTroyer, I'll need two power lines up to the pod, one for the chart plotter and one for a USB charge port. Do you think I can run a 14-3 wire and use ground for the return for both positives? I figure 14 wire should handle both loads easily.

 

[LeslieTroyer]

The only concern I would have is if you plug a noise plug into the 12v socket.

 

[sesmith]

Here's a link to a discussion on this same subject I asked about a while back. Read the replies concerning the skin effect with RFI transmission and why they recommend a larger gauge wire than you would think is appropriate. While you may never notice any issues, 14 ga. is likely too small.

https://forums.sailboatowners.com/index.php?threads/rf-drain-circuit.166068/#post-1151564

 

[Mark Maulden]

Ward, connect all your devices per manual. If you are worried about RF interference, you need to identify what a source of RF might be and protect from it accordingly. You probably have no sources unless you have high power xmttrs on board. Forget about discussions on skin effect vs wire size etc. You are not dealing with frequencies so high that skin effect becomes an issue. One could make a case that digital rise/fall times can fourier to high frequencies, however, wire inductance will slow those times and round off waveform corners which are the usual noise sources. As for yor USB port, run separate power AND ground up the pedestal. The power and ground “source” to be as close to battery as possible. Batteries are excellent noise filtering capacitors and who knows what noise source can be plugged into USB. You might also entertain running USB up the opposite pedestal tube for separation from electronics. As for the “drain” wire, if you are concerned, connect it to power negative.

 

[Ward H]

@Mark Maulden Thanks, nice explanation.