Re: [ukha_d] Slightly OT: Joining cables to be used under water....

["Geoff H"<yahoo@xxxxxxxxxxxxxxx>]

As an Oceanographic Engineer, I work with underwater cables all the
time. In my job I use proper underwater connectors and cable available
from suppliers such as http://www.pdmneptec.co.uk or
http://www.seaconeurope.com

However, for this application, I would try to replace the 1m cable with
a longer cable to eliminate the joint. This depends upon how the cable
is terminated at the pump. If replacement isn't possible (the cable is
potted into a compound at the pump) then use either a cable jointing kit
http://tinyurl.com/36dlzu or use Dow
Corning silicon rubber (732 or 734)
http://tinyurl.com/2ozamf over the
joint and when nearly set, cover with
self-amalgamating tape, followed by Scotch 33 PVC tape.

I have used the latter method down to 3500m in the oceans with great
success - several years use. This was joining rubber sheathed underwater
cable, and the rubber sheath was roughened using emery paper and cleaned
with an isopropanol wipe before sealing. It should work with PVC sheath,
but you would need to test it. Don't forget - not all silicon sealants
are the same.

One thing to consider with the cable jointing kits is the possibility of
the joint compound shrinking and cracking with low temperatures. The Dow
Corning silicon rubber is very good in this respect, you just need to
make sure that a good seal is made to the sheath.

Geoff


Vargster wrote:
> I've got to join two cables to make a watertight seal... how?
>
> To explain, I've installed a 1500 litre tank in the garden to collect
> rainwater to be used to flush the toilets in the house.
> There is a small pump in the bottom of this tank, to pump the water up
to a
> new header tank in the loft, before it comes down again to the
toilets.
>
> The problem is that the pump comes with a 1 metre lead power. It's a
> lightweight flexible mains cable, but it only carries 12V, I've got to
> extend this to get power to the pump outside the tank.
> The real problem is that the tank is 1.8 metres deep, meaning that a
lot of
> the time the joint will be under water...
>
> I've tried soldering the cables together, then giving it a couple of
thick
> coats of silicone sealant, which seems to work, but on further
inspection
> the sealant does bond too well to the cables outer sheath. Sanding the
> sheath to rough finish doesn't help either.
>
> Keeping the pump at the bottom of the tank seems the best plan as it
will
> generally be away from any ice that may form in the tank, though to be
fair
> I haven't seen any ice in there, even on days when my "control
bucket" of
> rainwater has 1/2" of ice on it.
>
> I've thought about floating the pump on a styrofoam pontoon on the
surface
> of the water in the tank, but the pump is the size of a coke can, and
weighs
> nothing, which causes a problem of what to do with the 15mm+ of fairly
rigid
> hose that takes the water out the pump and out of the tank...
>
> Any ideas, solutions, thoughts, etc gratefully accepted...
> Lee
>
> PS. Bringing it right back on topic, of course it's going to be
controlled
> by the HA server...
>
>
> [Non-text portions of this message have been removed]
>
>
>
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