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I'm building a simple plant watering station, which uses a relay-controlled submersible water pump (this one). The intent is to submerge the pump into a large enough water container to avoid frequent refills, but this means that the point where the pump's relatively short wires are extended will be submerged as well.

So here's the question: what is the correct way to insulate such joints? I'm currently using shrink tubing but I doubt it seals it well. Is there a better way?

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  • \$\begingroup\$ If you locate the pump differently, could you run the wires out a hole in the side or bottom of the container, which might be easier to seal? \$\endgroup\$ – user253751 Jul 31 '18 at 4:36
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    \$\begingroup\$ google "waterproof liquid electrical tape" \$\endgroup\$ – crj11 Jul 31 '18 at 4:46
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    \$\begingroup\$ Find yourself some IP68 splices. \$\endgroup\$ – Jeroen3 Jul 31 '18 at 5:44
  • \$\begingroup\$ 5V will hardly conduct in tap water if the surface area is small. I would tape it or heatshrink it and call it a day with a fuse. \$\endgroup\$ – MadHatter Aug 11 '18 at 21:23
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You can get "waterproof" shrink tubing that is lined with hot met glue. Low-cost waterproof tubing and splices are found on Amazon.

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I am not going to comment on how well this survives long term immersion, or that it is best for this job...

To make heatshrink waterproof you use a hot melt gun to smear hotmelt onto your wire, ensuring that it is continuously wetted all the way round, and for a 1" length. Then you heatshrink over it, which melts the holtmelt into a continous seal. You only need the minimum hotmelt for full wetting.

If you use clear heatshrink you can see if it is all sealed ok, and later, if water got in.

If I was doing it for under water, I would do the two wires separately.

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    \$\begingroup\$ Typical hot melt glues are not waterproof, but there are waterproof ones available. \$\endgroup\$ – crj11 Jul 31 '18 at 11:38
  • \$\begingroup\$ Tell us more. Where can you get it. \$\endgroup\$ – Robert Endl Aug 12 '18 at 0:46
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There are a wide variety of commercial to-code solutions to this. Search for “waterproof wire connectors”on Amazon to see some. Both butt crimp types and gel-filled wire nuts would work for you.

But for such a simple application, even $7 for a bag of connectors is probably overdoing it. Put a fuse in the line to protect the power supply, solder the wires, clean them, and then wrap with plastic electrical tape. With relatively clean water, that’ll last for years.

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Thank you for all the options. Looks like, given the gauge of the wires, waterproof terminal connectors would be an overkill, whereas the sealing quality of shrink tubing could be questionable.

Turns out Liquid Electric Tape was exactly the right tool for the job. Thank you, crj11!

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