DIY Watertight Junction Box For Serious Outdoor Sealing

Thingiverse user [The-Mechanic] shared a design for 3D printed enclosures that are made to house wire and cable junctions, which can then be rendered weatherproof by injecting them with a suitable caulking compound and allowing it to cure. It’s a cross between an enclosure and potted electronics. It’s also a one-way trip, because the result is sealed up like a pharaoh’s tomb. On the upside, it’s cheap, accessible, and easily customized.

The way it works is this: wires go through end caps which snap onto the main body, holding the junction inside. Sealant is then pumped in via the hole on the side, then the hole is plugged. Afterwards, all there is to do is wait until the sealant cures. [The-Mechanic] has a couple of companion designs, as well. For tubes of sealant that have threaded tops, one can more effectively save the contents of the tube for later with this design for screw-on caps. There are also 3D printed nozzles in a variety of designs.

One thing to keep in mind about silicone-based sealants is that thick gobs of it can take a really, really long time to cure fully. A thick gob of the stuff will tend to firm up on the outside but leave the inside gooey. If that will be a problem, maybe take a cue from Oogoo and mix in a bit of corn starch with the silicone sealant. The resulting mixture will be thicker, but it’ll cure throughout with no problems.

32 thoughts on “DIY Watertight Junction Box For Serious Outdoor Sealing

  1. Traditional RTV is not really recommended for use with electrical. It contains acetic acid which can cause corrosion. You can get electronics compatible silicone though as well as two part potting compounds that won’t have a hardening issue.

      1. Type 1 Silicone has the acetic acid and Type 2 Silicone has the methanol and ammonia. I had to double check with the referenced article and online since I’m not sure if the ammonia would be dehydrated also with methanol present (hygroscopic) or if the reaction requires water which I think it would and if the reaction would consume not allowing the ammonia to react to form complexes or hydroxides. I’d have to read into a little more. Therefore, Type 2 Silicone could have issues also with copper. Seems like you could spray a layer of clearcoat epoxy or Krylon or something that doesn’t react just in case before potting. Thinking would be good to go then.

    1. Yes, use “acid free” or “neutral curing” silicone. This is also used as “bathroom RTV” when you have delicate walls or flooring like marble. This calcium carbonate based material will be destroyed by acids.

  2. Be aware that while this may be both waterproof and electrically insulated, most plastics will become brittle left exposed to UV from the sun. Maybe apply some protective paint for good measure?

    1. With any luck the silicone will be fully cured by then leaving a firm blob to keep the connection together. If the connection was going to be regularly submersed in water this DIY solution isn’t a bad alternative to (expensive) off the shelf fittings, but for “it’ll get wet” type applications, rubber tape will hold for years without issue.

  3. Not to rain on anyone’s parade. But if I need something I need to weatherproof, I’ll stick with what the NEC will prove for use in environments where there is an explosion risk. Unless it could affect me directly I don’t care what methods others use.

      1. Meaning – Ex d, protection by flameproof enclosure is not necessarily hermetically sealed. You have flame paths that will extinguish and cool any flame/explosion or hot gas propagating through. But you are also allowed sintered breathers filters, and they very much water permeable.
        Flameproof is not a warranty for a hermetically sealed enclosure

        1. Ex d has to dissipate any potential energy storage safely. I remember being puzzled when I had to learn all the differences in Ex and IS ratings.

          Breathers confused the crud out of me untill I had the flame path bit explained.

          You want to be able to let an overpressure out of a confined space, rather than blow the lid off. Makes sense from that.

          AAAAND then there’s ATEX and all that fun.

  4. I’ve been doing something similar for years but a much easier way. solder or connect the ends however you want then bring your heat shrink tubing over the top of it then flood the inside of the heat shrink with silicone then use your heat gun on it. I have yet to have one fail. Plus i don’t have to wait an hour or so to print one just cut away the heat shrink tubing i need and go.

  5. Looks quite practical, but I wouldn’t necessarily rely on the selant alone to provide strain relief for the cables. If this is printed for a particular cable diameter a few countering teeth on the inside of the endcaps may do a decent job. Or maybe just a ziptie or two?

  6. vulcanised rubber tape…if properly applied, the isolation is the same or better then the uninterrupted cable. Remains flexible, leaves no goopy residues, can be removed by a simple box cutter. Withstands rain, sun, wind, snow or any combination of them.

  7. This is ridiculous. First off, you don’t need this much effort — unless you’re actually going to bury the thing, just use a metal box with a grounded outside, and put inhibitor on the connections. It’ll be fine for years and years, a lot longer than this plastic will last.

    Second, it won’t work for anything. If you have a flexible caulk up against a wire’s insulation, even thermal cycling will cause the two to separate. Water will seep along the interface. If you want to seal it, use a pressure fitting, a rubber washer actually compressed between the wire’s insulation and the box.

    Third, it really won’t work. A common technology for buried wires is to put them in a bit of PVC conduit, it’s almost the same stuff as pressurized water pipes. They even glue it with a real solvent. It really could be waterproof, in principle. But ask any electrician who’s ever dug one of these things up. The conduit is *always* full of water.

    Use inhibitor at joins, and where safety matters, have an exposed ground.

  8. DIY electrical is still DIY. The author could of easily had the box in a outdoor box with a couple strain reliefs. I can see if working great until someone trips over his cord that fell because the zipties failed. The electrical code isn’t half as bad here in CA if you understand its purpose. I’m not sure I would call anything DIY electrical 100% safe – and not include a ground wire.

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