Cable option....

Genesis

Here's an interesting discovery I thought I'd share....

I do a lot of marine wiring. A LOT. Some on my boat, some on other boats. The "others" usually come about when I run into a friend on the dock who has some butcher job from a boatyard that isn't working and I sort it for them for a six-pack - or sometimes more, depending on exactly how involved it is.

Anyway, in the course of this last year I installed a set of fuel flow meters on my boat. They required a fairly long run of multi-conductor, shielded wire for the senders - the senders are on the other end of the boat and comprised of optical encoders - this is a digital system and as such is quite sensitive to noise and such.

Well, after much searching I found a cable that met my specifications for use in the marine environment. Its Ancor #158010; 20/8, 100% tinned conductors with shield.

Pretty tough stuff, and arranged as 7 around with 1 inside as a core, so its very crush resistant. A heavy PVC jacket and decent flexability rounds it out.

Anyway, today I started looking into cables to use for my Rebreather project, and this stuff was sitting in my shop. I checked diameters, and made a startling discovery - it fits VERY nicely right down the cable glands that Salvo and others use! The lack of a crushable "fiber" inside means that it should work well under compression, especially if you wick some epoxy up the cable before you put it into the gland and tighten it down (let it kick first!)

I'll post more on this once I've had a chance to play with this stuff in real life, but it sure looks good at the outset. If you waterblock both ends a nick in the jacket shouldn't affect its overall integrity, as you'd need to penetrate the individual conductor sheath first. If you go to Fischer connectors on each end then outer jacket integrity becomes fairly irrelavent to performance.

Best part? You can order 100' spools of this stuff from West Marine at a rational price. Its not usually stocked, but they can get it within a few days.

Pierre Farrugia

Hello,

When you say you use epoxy to seal the cable.....can you explaine in more detail, what type of epoxy to use and where exactly to put the epoxy? Sorry if this is a stupid question, is glue and epoxy the same ? (English is not my spoken language...)

Thanks

Pierre

__________________
Pierre Farrugia

My wife told me " If you don't quit diving I'm going to leave you"
My reply " God, I'll miss you"

www.atlam.org www.divemed.com

Genesis

One of the problems I've run into before (and so have dive-light makers) is that the cable jacket will crush over time. If you use a cable gland this leads to a leak!

So what I've taken to doing is to take the cable, insert it through the gland, strip back the outer jacket and then "paint" the outer/inner jacket interface with epoxy - standard laminating stuff (e.g. West) that I have for general-purpose use around my boat and home. I use a slow hardener; this gives it a good long while to soak in before it kicks off.

It will "wick" up the cable jacket a significant distance (1/2" or so) and then set up into a hard, water-impervious block. When the gland is tightened down around THAT, it doesn't give - thus, no leaks.

You can also "paint" the stripped-back ends of the cable after you solder everything up if you want for even more protection.

One of the primary ways that wire fails in the marine environment is from the salt air wicking its way up under the jacket. This is why the use of cheap wire that is not 100% tinned is foolish on a boat - the wire will wick up salt air up under the jacket and corrode internally, where you can't see it - the conductors literally turn to green powder! The wire LOOKS fine, but doesn't conduct electricity any more because its just a jacket with a powdered conductor inside......

100% tinned wire is resistant to that, but not proof against it. The solution is to seal both ends; Starbrite makes a liquid electrical tape that works pretty well; you paint it on and it sets to a rubbery consistency that retains some flexability. I don't like silicone sealer because it releases acetic acid during the cure - and that's corrosive. Better is something like 5200 (a marine polyurethane sealant) although its hell to work with as its extremely messy. But for truly extreme conditions epoxy works even better - just paint it on where the wire is stripped back from the jacket. The only downfall to this approach is that there's no flexability to epoxy once it sets up, so this only works for immobile portions of the cable assembly (e.g. under a connector housing, etc) Now the only way water can get to it is for the jacket to be physically damaged. If you use a wire like the Ancor I cited and seal the gland ends with epoxy, there are two jackets (the outside and inner core jacket of one of the conductors) that must be damaged before water can get in there. Hopefully you'll notice the outer jacket breach and replace the cable before the inner breach happens.....

Another approach is to use hermetically sealed Fischer connectors on BOTH ends. Now a cable breach doesn't damage anything except the cable itself, as there is a hermetic seal between each end and the electronics behind it at the connector.