Shielded cable for autopilot install.

[Anode]

I in the middle of my Simrad AP install and the manual calls for shielded cable for both the main power supply and the run to the hydraulic pump. The length of run to the pump is minimal with a 12awg wire but should work.

Beldon makes a 12 AWG - 19x25 Stranded Tinned Copper Multi-Conductor - Shielded PVC Electronic Cable but haven't been able to find it in cut lengths. 1000' role seems to be the only option.

Anyone know of a source? 50' would do it for me.

Thanks Chip


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[Tom.B]

Shielded power cable? That's a new one on me. I thought the voltage and amperage was high enough in power cable to overcome outside radio interference. But hey... what do I know? ;-)

 

[Anode]

It caught me by surprise too. I actually have standard marine wire pulled for the installation and then I got to the page that said 'shielded wire'. If that's the case I'd rather replace it now rather than later. Don't want the boat to turn to port everytime I key up the SSB.

 

[JD]

GonzoF1 wrote:
Shielded power cable? That's a new one on me. I thought the voltage and amperage was high enough in power cable to overcome outside radio interference. But hey... what do I know? ;-)

*The problem is inference going out as well as coming in.* The shielding might be for other components (VHF)*to not pick up the RF form the pump.

 

[Tom.B]

Ahhh... Funny that I only think of shielding as keeping noise out and not the other-way-round. LoL It has to say something about my overall thought processes.

 

[FF]

Building our 90/90 we used shielded cable for EVERY circuit.

Tiny bit more expensive and its insurance against a lightning side strike (we are in FL).

 

[Capn Craig]

Chip,

Try McMaster.com** Do a search for shielded electrical wire.* look at the catalog pages around 785 +/- a few pages.**They have a huge selection of shielded, tinned copper, in various jackets, heat, and service ratings.**Cut lengths areno problem.* And if you see it in the catalog, my experience is nearly everything is in*stock, and can ship today.* I get next day delivery for the standard UPS shipping here in Iowa from Chicago.* It might be a day longer to MO, but there service is phenominal.


-- Edited by Capn Craig on Friday 2nd of December 2011 01:06:32 PM

 

[Singleprop]

FF wrote:
Building our 90/90 we used shielded cable for EVERY circuit.

Tiny bit more expensive and its insurance against a lightning side strike (we are in FL).

*FF, interesting.

I don't know much about this - can you explain what effect shielded cables have compared to non-shielded cables?

*

 

[C lectric]

I'm no expert here but I've had some experience with industrial systems using stuff like this.

The sheild protects a signal carrying wire from outside electrical interference. Lots of signals can be altered as they are usually low power/voltage and can be corrupted easily if not protected. There are other ways of doing this in some cases.

High power cables sometimes are sheilded to prevent the opposite, sending out electrical interference, , particularily if the power is turned on/off or reversed abruptly. That would be the case in an autopilot, I think, at least some of them, as the controller will adjust power levels and polarity in a reversing motor setup and power might be pulsing. Stepper motor, AC variable frequency and adjustable reversible DC drives would fit this category. My own AP is of the last category.

The interference can be of concern particularily where a lot of wiring of different types is in close quarters. For example some folk I knew had a problem with a VHF transmission causing the A.P. to do a sharp turn. Not common then , less now I think, because newer equipment is designed around this and that may include sheilding wiring.

 

[RickB]

For the application you guys are talking about, unshielded twisted pair (UTP) signal wiring is adequate. As a matter of fact if you are connecting this stuff to the displays and navionics equipment you may be better off with twisted pairs unless you understand what can happen with grounding the shield at one end only or both ends.

 

[Tom.B]

RickB wrote:
unless you understand what can happen with grounding the shield at one end only or both ends.

*Giant antenna?

 

[C lectric]

No, well maybe, but the problem can be ground loops, a circulating current in the shield itself, and that can cause more trouble.
Usually the mfgr. will tell you specifically what is required.
Often the bonding of the shield is to be done at one end only, usually the control end. That way there is not a continuous shield circuit to allow a current flow.
However, if the mfgr. is specifying a shielded wire/cable they should also tell you what specifically is to be done in this matter and often will recommend a certain cable type.
RickB has a point about a good twisted cable.