C5: A low-cost reliable waterproof connection for continuous immersion

Over the past year at AusOcean we've been experimenting with various ways to make low-cost reliable waterproof connections. We explored this path after reaching the conclusion that most so-called "waterproof glands" either do not cope with continuous immersion and/or they cost too much. In fact, one can easily spend more on a single waterproof connection than on one of our underwater cameras.

We have therefore decided to make permanently "potted" connections, rather than re-usable connections. Potting is the process of filling an assembly with a solid or gelatinous compound. We call our connections Cylindrical Cemented Cold-welded Caulked Cable connections, or C5 connections for short.

To make a C5 connection you will need the following:
  • A PVC tube - the "cylinder" (which holds everything in place).
  • PVC glue - the "cement".
  • JB Weld - the "cold-welding" agent.
  • Marine-grade Sikaflex 291 - the "caulk".
  • The "cable"
Naturally, you will also require the PVC part to which you are attaching the connection. In the example below we make a data cable connection for a PVC end cap.


Here is the step-by-step process in photos:

1. Position the tube on the surface.

2. Use PVC cement to glue the tube on. Ensure there are no air gaps.

3. Drill a hole and feed through the cable.

4. The sheathed part of a data cable should protrude about 1cm.

5. Ensure the cable is centred. Tape it in place if necessary.

6. Tape the cable, leaving at least 1cm at the bottom bare.

7. Fill the bottom 1cm of the tube with JB Weld and wait 6 hours for it to cure.

8. Remove the tape.

9. Flood the tube with Sikaflex and taper it up the cable at least 4cm.

9. Tidy up with electrical tape.

Here are some tips:
  • If making a data cable connection, strip the last 10cm of cable ahead of time.
  • Make sure the JP Weld completely fills the bottom 1cm of the tube.
  • Make sure there are no air bubbles in the Sikaflex. 
  • A stiff piece of plastic or a cable tie makes a useful tamper.
  • Don't forget to tape the cable, but leave at least 1cm at the bottom without tape. The goal is to have JB Weld bond to the bottom of the cable, and for Sikflex to bond to the rest.
  • Ensure that the JB Weld is completely hard before applying the Sikaflex. 
  • Take your time!
With care you can make a low cost and reliable waterproof connection.

To date, we have successfully tested C5 connections to a depth of 20 m with continuous immersion for months at a time.


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