[PSUBS-MAILIST] minn-kota cabling to hull

[Stephen Fordyce via Personal_Submersibles]

Hi Jon,
I did an experiment with this recently for my underwater caving light:
- Cable gland (no-name Chinese brass one, which I have since successful
tested to 160m!)
- 2-core (1mm2 I think) twisted pair cable with pretty solid sheath (ie. no
air spaces), ~6mm/1/4" OD
- External pressure: 80m water depth
- Pressurising medium: air

The cable didn't extrude or otherwise move, but the leakage through the
wire strands was significant (ie. comfortably audible without being too
loud, and slightly too much to blow bubbles in soapy water).

I didn't measure it, but the flow would be less for water, and probably
wouldn't be filling up your sub too quickly.

Something to point out on the inside/outside cable glands is that the
loading on them is much different with external vs internal pressure.
Ie. for external all the force is compressing the fitting against the hull,
whereas for internal the threaded section is in tension (and some are not
very thick).  I don't think typical cable glands are meant for internal
pressure, but the Blue Globes are probably good for it.

If anyone is interested, the cable glands I used and tested are these:
http://www.aliexpress.com/snapshot/6439871078.html?orderId=65381957659001
(the O rings are a bit average, and I doubt they would be much good for
internal pressure, but otherwise shiny and good quality, with 100% success
on sealing for 4 of them to 160m)

Cheers,
Steve

On Fri, Apr 17, 2015 at 8:23 AM, Jon Wallace via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

>
> Alan,
>
> The best approach is to use threaded rod with the potting, if possible.
> My question is probably better stated in the context of whether air trapped
> between a multi-wire cable and the surrounding sheath is an issue to be
> concerned about.  Some cables have a good tight sheath but others such as
> CAT-5 is pretty sloppy.
>
> A potential concern of the blue globe gland since it seals around the
> cable sheath is what happens if the sheath gets damaged and cut
> underwater.  Water pressure will allow creep to flow between the wires and
> sheath bypassing the gland.  However the same would be true of a home-made
> potted penetrator as well.  What type of inflow should we expect from such
> a breach?  Minor?
>
> Jon
>
>
>
>
> On 4/16/2015 4:46 PM, Alan James via Personal_Submersibles wrote:
>
>  Jon,
> I noted that the lights on "I think" a dual DW at Nuytco
> had oil in the wiring tubes to the lights, which were a clear plastic.
> I compensated a linear actuator & didn't strip the wires inside the
> potting.
> I filled it with WD40, & it just ran out between the epoxy & the wires when
> I tipped it upside down. No pressure applied.
> I think it was Hank that suggested untwisting the wires so the potting mix
> can get around them. On the through hulls, Carsten & Emile are using
> blue globe cable glands with one outside the hull & another inside for
> double security.
> Alan
>
>   ------------------------------
>  *From:* Jon Wallace via Personal_Submersibles
> <personal_submersibles at psubs.org> <personal_submersibles at psubs.org>
> *To:* Personal Submersibles General Discussion
> <personal_submersibles at psubs.org> <personal_submersibles at psubs.org>
> *Sent:* Friday, April 17, 2015 12:06 AM
> *Subject:* [PSUBS-MAILIST] minn-kota cabling to hull
>
>
> I think Emile had details of potting the minn-kota.  Anyone know where
> this might be located?
>
> Anyone waterproofing their cabling by oil-compensation through a poly
> tube?  If I remember correctly, Aquarius uses this method for the
> electrical wires to the lights and vacuum.
>
> Jon
>
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