Under-water control cable joints

[jhovel]

As the title implies, I need to make a couple of low voltage connections which will be under water (up to 1.5m below the surface of our water tank). I need to fit a couple of reed float switches inside my tank and can;t do them through the wall. The two wires from each sealed switch are only about 200mm long. So I need to solder cables to them and seal the joints.
What options are available? Shrink sleeves with glue inside them are available, but the staff at the local shop couldn;t guarantee that they would be water pressure proof. I wondered about filling shrink sleeves with silicone before shrinking them.... or fitting glue-type shrink sleeves and then encase them in longer spagetti sleeves filled with epoxy, for example.
What's available for the purpose, please?

[Pearo]

As the title implies, I need to make a couple of low voltage connections which will be under water (up to 1.5m below the surface of our water tank). I need to fit a couple of reed float switches inside my tank and can;t do them through the wall. The two wires from each sealed switch are only about 200mm long. So I need to solder cables to them and seal the joints.
What options are available? Shrink sleeves with glue inside them are available, but the staff at the local shop couldn;t guarantee that they would be water pressure proof. I wondered about filling shrink sleeves with silicone before shrinking them.... or fitting glue-type shrink sleeves and then encase them in longer spagetti sleeves filled with epoxy, for example.
What's available for the purpose, please?


This is a subject that will always start fights among sparkies. BUT, I have experience with pressure sensors submerged to 1000'+ of water. The only way to guarantee a waterproof seal is to pressurise the joint so that the internal pressure is greater than the external pressure.

BUT, this is a tank and only at 1.5m depth of water. In my experience, double wall heatshrink (the stuff with the glue lining) is ok for a while, until the glue becomes hard and brittle and then it leaks. This only takes a few months. The best stuff is 2 part silicon in a shrink tube, but failing that my favourite seal is some decent quality silicon squirted into heatshink, and the using the heat gun to shrink the seal down. It still fails from time to time, but it outlasts any other solution outside of positive pressure.

Epoxy is also crap. The problem being the thermal expansion of various materials. A hard plastic combined with a flexible plastic is a recipe for failure. Think thermal expansion.

[DavidG]

Dow Corning silicone grease inside heat shrink. Remains flexible.

[_fly_]

I vote for silicone inside heat shrink as well.
That's the way I solder my pawn globes up although they only go about a metre deep.

and make sure the heat shrink is a good 1.5 inches over the wire shielding, so if your solder joint is half inch of bare wire, you'll need 3.5 inches of heat shrink.

[droog]

How about this stuff, available from Jaycar or off fleabay.

http://www.starbrite.com/item/liquid-electrical-tape

[Wrongwayfirst]

Also try a reputable irrigation shop. Controller wiring is 24VAC and joins are buried underground. I know this is not submerged but ground can and does get very wet when it rains. Many years ago they used to have gel joiners 3 or 4 different styles, some were even the style of Ethernet where you pushed the sheathed wires in pushed the "button" home and little bit gel squirt out so you knew join was good.

After many any years they can have only improved on these joiners and th cost was bugger all from memory.

i never used one totally submerged but I have had a pit fill with water and when it dried out all was good, so I know it's not 1.5mtrs but a combination of all ideas may be your solution
cheers

[RustyArc]

Many years ago they used to have gel joiners 3 or 4 different styles, some were even the style of Ethernet where you pushed the sheathed wires in pushed the "button" home and little bit gel squirt out so you knew join was good.

They're still around, they're just big versions of snot blocks that are used for phone:
http://www.irrigationstore.com.au/Product/ProductDetail.asp?lngProductID=95

Don't know if I'd call them cheap.

I'll give another +1 for neutral cure silicone and heatshrink.

[jhovel]

thanks guys. I would have given the silicone in heatshrink a go.
However, when I discussed the options presented here with a friend tonight (also a forumite), he offered me a better solution: he gave me an external weatherproof switch with a float on a nylon line made for exactly this purpose. |It has a weight at the bottom and adjustable stops for the float to set the on-off interval for the pump. This will keep my cables right out of the water. Beaudy mate and thanks a lot!