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I am using a Polyolefin Adhesive-Lined heat-shrink tubing to water-proof wire joints.

The method works well but I need to measure if the seal is truly water-proof. The datasheet provides a test method:

Prepare 3 test assemblies insulated with SCT-2 as follows: Construct a 2-wire to 2-wire inline splice in any suitable manner (crimped, soldered, twisted or welded). Splice an AWG 18 and an AWG 14 to an AWG 20 and AWG 14. Each wire shall be approximately 12 inches long. The wire insulation shall be cross-linked polyolefin and the conductor shall be bare copper. Shrink a 2-inch length of SCT-2 over the splice area with an appropriate heat gun. Apply heat until the SCT-2 is completely recovered on the splice and the adhesive liner flows at both ends. Allow the test assemblies to cool to room temperature and immerse them, except for the ends, in a 5% salt solution for 24 hours at room temperature. Apply 50 volts DC to the immersed specimens and measure the current leakage.

I do not understand how to measure the current leakage. I get it that the input current will be exactly equal to the output current if the seal is truly water-proof, but if the seal is not water-proof where else would the current flow anyway?

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  • \$\begingroup\$ This doesn't answer your question, but may set your mind at little more at ease - I've used adhesive-lined heatshink boots to cover & seal joints & splices in cables which were used at 100m-120m depth in seawater and survived for well over a month (that's just how long the equipment was used for - the joints didn't fail). \$\endgroup\$ – brhans Feb 21 '16 at 14:00
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schematic

simulate this circuit – Schematic created using CircuitLab

Figure 1. Test setup.

You don't run current through the conductor. You just apply voltage to one end of it relative to the other electrode in the tank it. If the splice insulation is good no current will flow.

Figure 1 shows a second electrode. If a metal tank is used it could act as the electrode.

Current limiting

I recommend that some form of current limit be added to the circuit. Without it you risk damaging the ammeter in the event of a bad insulation breakdown or accidental short-circuit. I presume you are interested in leakage currents in micro-amps which would equate to a leakage resistance given by \$R = \frac {V}{I} = \frac {50}{50\mu} = 1~M\Omega \$ for a 50 uA leak. Setting R1 to 10k would limit the short-circuit current to 5 mA and give a 1% error on a 1M leakage.

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  • \$\begingroup\$ Thank you for the edit. One question, I am worried about safety. Will current passing through water cause H2 to be released? I am worried about a fire if something sparks. \$\endgroup\$ – Saad Feb 22 '16 at 15:02
  • \$\begingroup\$ Any significant electrolysis would take a large current (many amps) and you won't have this (if your splices are any good!). In electrolysis the hydrogen and oxygen are collected separately but you have no collectors so they would just disperse and possibly recombine at the surface. \$\endgroup\$ – Transistor Feb 24 '16 at 7:54

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