Cables - for water immersion & weather exposure

[DTJ]

What are folks experiences with cables in applications where they could be out in the sun and weather and permanently immersed in either salt or fresh water?

There are cables that have powder impregnated water blocking thread in them or water proof jelly but they are expensive and hard to find. I'm looking for cable options for an instrument and not making progress.


The signals carried by the cable would be no more than 12V at a maximum of 100mA or so, probably much less. A life of 5 or so years would be nice.


If the cable sheath was damaged and water did manage to flow inside the cable it would be stopped by polyurethane encapsulation in the submerged instrument.


What's a good mechanically tough and weather resistant sheath material PVC, Polyurethane, Polyolefin, LSZH, MPPE?
Lots of choices, what have others used?

Edit:

It's for a commercial application.
OD needs to be smallish, <8mm.
3 or 4 conductors would be ideal.

[kaz911]

for such little power - can you use good quality shielded outdoor CAT5E cable? that is pretty tough and can be put in ground directly without further protection. I don't know how it will hold up to salt water though.

Alternative is to buy a boat shore-power cable - they can resist a lot. They are big and heavy but can live for ages even in harsh salty water and high UV (I have seen them work for 8+ years in the middle east with people stepping on them daily and partly submerged in 43-45ppm salty water. (That is about 25-45% more salt than "normal" in most places) - but buy a EU/240v version as the US version is 110v and is very thick and heavy as it needs less copper to carry the voltage and current.

[dmills]

Polyurethane is standard in the sonar industry, but even then be a bit careful, we had a reel of PU jacketed coax that after 6 months in the lake turned out to be slightly permeable, eventually got from the manufacturer that they had changed an ingredient and had not re checked, swearing was copious.

You can get a PU jacketed cat 5 as an off the shelf item, that we found to be acceptable for low current stuff as long as it was not flexed too much.

One thing that helps is a thick jacket (for both mechanical robustness and damage resistance), and under water cables with 2-3mm of outer jacket thickness are not uncommon (~10mm OD).

Be very careful about that assumption that the potting of the underwater device will save you from water that gets into a damaged cable, this depends critically on the PU wetting out the individual wires adequately, and that is not a given (Teflon insulation can be a particular pox this way, there are chemical treatments that will help).

73 Dan (Who used to do underwater transducers for a living).

[e100]

For the actual cable look at what they use for diver's umbilical cables.

For sun and mechanical protection, run your cable inside some black polyethylene irrigation pipe. You can get 13 and 19mm from your local hardware store. Cheap and will probably last 15+ years. If you need more flexibility use a garden hose instead of poly pipe. It should survive 5+ years. If you need crush resistance, use corrugated PVC conduit.

The newer "modified silicones" typically sold as bath and shower sealants have reasonable adhesion to many materials and can be applied as sun screen to things that are degraded by UV.
If you want an example of really cheap, I have a temperature sensor in a water tank that is only protected by being encapsulated in self healing silicone potting compound inside a short piece of hose pipe. This is joined to the surface using PVC "alarm cable". No problems so far.

[DTJ]

Kaz911
Ca5 5 buriable cable would be good except I' chasing only 3 or 4 inner conductors. It's certainly priced well. Unfortunately the boat-shore cable would be way too bulky.

Dan
I have come across some PU cable. Great stuff but pricey. To try and keep water out of the potted part we weave the inner conductors back and forth a bit prior to getting to the PCB to make the "leakage" path longer.

e100
The irrigation pipe is great stuff and hardy but not really suited to my application.

[barry14]

In the sonar world, we found the best material for cables is polyethylene.  It will survive seawater immersion for years.  There are special underwater cables that are water blocked so if water intrudes it will not travel along the inside of the cable.  This is done by filling all of the empty space in the cable with polyurethane or similar material.  However these cables are difficult to wire because of the extra material.

[stj]

you can get "arctic" rated cable, but wouldnt your application need it to be screened and/or twisted-pair over any real distance?

[DTJ]

Polyurethane sheath is looking like a good option if i can find it at a reasonable price.

A foil shield and 3 or 4 cores twisted should be ok.