Heat shrink as water insulator

If you coat the end where the wire goes in with 60min epoxy, it could probably hold much longer.

 

Make sure you are using the right heat-shrink tubing. For a waterproof seal you need to use tubing that has an adhesive coating inside that melts when the tubing shrinks. Find some here.

 

Here is a little video that shows how to check conductivity. I think this would be the easiest way to check,

 

I don't think much of this guy's method of "estimating conductivity". Working with a setup that makes it that easy to short out a lead-acid battery is freaking dangerous. He might at least have stuck some low-resistance current-limiting device in the circuit, at a battery electrode, so any short won't cause a fire or send hot drops of molten copper flying, or worse.

For the OP's purpose, I would just use the ohms scale of a multimeter and add a pinch of salt to the test water to ionize it. That should show if any water is getting in.

 

First even heat shrink that has "adhesive" may not give you the seal that you are looking for (one that can handle flexture). The adhesive is sometimes similar to what is found in hot melt glue and can be somewhat rigid. Sometimes RTV can be applied to a solder joint and heat shrink placed over it. The RTV should eventually cure and can give you a waterproof seal.

Secondly, distilled water is a poor conductor. Fire experts giving demonstrations of why water should not be used to extinguish electrical fires often run house current to light a lightbulb through a jar of water. To make sure that the water conducts, they sometimes add sulfuric acid. I am not sure if adding vinegar to the water would produce a similar effect, but something may have to be added to water to enhance conductivity.

 

Raychem or similar as Hevans says WILL be both waterproof AND flexible.
Used it many times in underwater application on cathodic protection.
Samples of our idea once won an international engineering award .....trouble was the bloke who won it , stole our idea.....
Even had the hide to use the cutaway section I made.

 

RTV...brand of silicone sealer
When used in electrical applications, non-acid type should be used.

 

Room Temperature Vulcanizing / ation . . . . . . or in the chance that it doesn't work for you . . . . . .Return To Vendor by riding there on your Rugged Terrain Vehicle .

 

Your picture shows 3 cables; if they aren't all connected, why not go down the road of the Electricians and use an insulation tester, testing before and afterwards?

 

There are several non-electrical approaches, none of which you are likely to be able to employ unless you have access of laboratory-grade equipment.

The simplest method requires an analytical balance to perform a "before and after" weight measurement. You take your "test sample" as shown in your images, and place it in an oven at about 100C for several hours to evaporate all moisture content, including any moisture possibly "trapped" under the insulation. At 100C any water present will turn into vapor (steam) and escape from whence it entered. I would do this heating overnight just to make sure any and all water was removed. For really good test results, do this under vacuum and measure the vacuum pressure. When the vacuum pressure ceases to decrease, no more water can be removed.

Weigh your, now dry, sample with the analytical balance. Record the weight to micro-gram or better precision if possible. Next, immerse the sample fully under water and allow it to remain under water for several hours, overnight preferably. Do this after weighing the sample, while the sample is still warm from the oven. To help speed the penetration of water through any leaks in the insulation, it helps to pressurize the water containment vessel with air or nitrogen.

After removing the sample from the water vessel, blot-dry the outside of the sample by wiping with a paper towel to remove all visible signs of water on the outside of the sample. Use several sheets of paper towel, inspecting each afterwards for any indication of water on the sheet. If you want to be sure, weigh each sheet before and after wiping the water off the sample. When the before and after sheet weight does not change, you are done wiping.

With the outside of the sample now dry, weigh the sample with the analytical balance. Any increase in weight from the previous "dry" weight measurement is a positive indication that your "waterproof" insulation has failed. Try again using one or more of the previously submitted suggestions for waterproofing your connections.

There is also a procedure, similar to the above water immersion test but which uses helium gas and a helium mass spectrometer leak detector, that you are even less likely to be able to perform; however, it is the "industry standard" for non-destructive leak testing of hermetically sealed assemblies. Worth investigating if you can gain access to the necessary equipment.

Perhaps you should consider renting or purchasing an electrical insulation tester.

 

RTV is also what we used to use as suggested by Raychem-Chemelex for underwater cables.
Fill the Heatshrink with RTV before shrinking.
M.

 

To your point of wanting your conductivity test, as you described, to work...
Add a few DRY salt crystals alongside your wires under the shrink wrap.
If all is well - a few DRY salt crystals should not matter.
If all is not well - you will know it.

 

A little common salt from your kitchen will be enough for the water to become conductive. Then you can try.