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I have a small 12v aquarium pump (submersible), and I'd like to hook it up to a small solar panel and put it in an outside pond. This would mean cutting some leads and soldering. Pretty simple job. For inside work, I would usually just put some electrical tape or heatshrink around the joins, but in this case, the joins will be exposed to the weather (but not submersed in water).

What's the best way of waterproofing joins like this? Heatshrink + silicon? Hot glue? Something else? If there are multiple options, what are the pros and cons of each?

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In order from lowest to highest cost (roughly):

1) For something simple like this, grease filled wire nuts aren't the most beautiful option, but you can readily pick up a pack of them for a few bucks at your local hardware store.

Pros: Cheap, available, work
Cons: Messy if you need to disassemble, clunky, look bad

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2) You could also use grease-filled IDC (insulation displacement) connectors.

Pros: Cheap, available
Cons: Like other IDC connectors, not great at high current, messy to service

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3) Use adhesive-lined heatshrink tubing. It works just like heatshrink, but has an inner liner of hot melt glue which will melt as the tube shrinks, creating a (mostly) environmentally protected connection.

Pros: Moderately easy to service, fun to shrink, looks clean
Cons: More expensive, is stiff when finished (can cause stress risers in the wire)

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4) Use adhesive-lined crimp splices or adhesive-lined solder splices. Outer sleeve is similar to adhesive-lined heashrink but is usually transparent for inspection. Crimp style are crimped, then shrunk. Solder style have low temp solder pre-applied inside, just insert the wire, apply heat, and you've got a waterproof solder splice.

Pros: Professional, adhesive layer can be inspected to ensure full coverage
Cons: Really, really expensive.

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    \$\begingroup\$ I would add option 0: Just solder the wires and add tape. For this application it should work fine. Low voltage, low current, and no real safety issues. The downside is that it will eventually fail, but there is a good chance that it will last 10+ years. Keep in mind that most (all?) automated sprinkler valves use 12-ish volts and just use wire nuts with no tape or grease and work fine. \$\endgroup\$
    – user3624
    Jan 16, 2013 at 2:30
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    \$\begingroup\$ @DavidKessner Yeah, I know it's not dangerous, I'm more interested in making it long lasting. \$\endgroup\$
    – naught101
    Jan 16, 2013 at 2:42
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    \$\begingroup\$ @user3624 - Swap "tape" for good quality self-amalgamating tape and it'll last decades. Is a bit more spendy though, as is any solution that really works. \$\endgroup\$
    – John U
    Mar 3, 2014 at 14:58
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    \$\begingroup\$ I have done both #1 and #3 for underground wire that was exposed to water and they both failed within a few years. So then I tried the splice and put a tube over it (the tube was slid over the wire before joining) and filled the tube with silicone caulk and it has held up fine for over 15 years and still going strong. \$\endgroup\$
    – user103157
    Mar 11, 2016 at 3:35
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Take a piece of small clear tubing, slide it over the wire. Splice the wire together, and then fill the tubing with silicone caulk.

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  • \$\begingroup\$ As long as your wire isn't generating too much heat, anyway. \$\endgroup\$
    – Conrad Meyer
    Mar 3, 2019 at 17:10
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I've used Bulgin Buccaneer waterproof connectors with good results. Yes they are more expensive than heatshrink or solder splices, but if you need to disconnect and reconnect in the future this works and is not that expensive. Various power and data options are available.

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Another option you could use is electric liquid tape

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Get small plastic container or small plastic bottle. Make a hole at both ends (if not a bottle) Thread spliced, taped cable through and seal one end. Then pump with silicone until full and airtight. Secure both end of the unit. Wait until dry and hard. I did this with my garden pump when I had to replace it and 10 years on it still working perfectly.

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