7.26.2015

Connectors and Cord Grips – Waterproofing our Wiring


One problem with having a waterproof chamber in our submersible is finding a way to get wires in and out without compromising the seal. We have three separate measures that we are taking to make sure that all of our wires are waterproof: we are using five cord grips, a waterproof 3-pin connector, and strategic epoxying.



Cord Grips:

Cord grips allow us to have wires penetrate the waterproof compartment without having to worry about letting water in. We bought submersible cord grips from McMaster (pictured below) and incorporated them into the design of our watertight compartment.

Submersible Cord Grip


As you can see in the picture the back end of the cord grip is threaded which allows us to easily incorporate it into the plugs for our waterproof chamber. Because we are getting the plugs professionally machined we can be confident that they will be tapped correctly, meaning that with the addition of some Blue Loctite the threads will be waterproof to a few hundred feet. Lastly the inside of the cord grip has rubber pieces that tighten around the wires to ensure no water gets past.



Epoxy:

While the cord grips take care of most of the possible entries into the waterproof chamber it leaves one - water that gets inside of the insulation of our wiring and travels through the wire itself and into the chamber. To keep this from happening we will epoxy the endpoints of the wire on both the outside and inside of the waterproof chamber so that even if one is to leak a little the other should keep the water at bay.



Waterproof Connector:

The last piece in our waterproofing system is a waterproof connector. We are using one of these outside of the submersible as a way to easily attach/detach the tether from the submersible. We spent a long time looking for connectors that are actually submersible and not just waterproof as we ran into a few common problems. In a majority of cases connectors are rated as IP67 or IP68, neither of which are submersible (IP68 is submersible but usually only to shallow depths and for limited time, for more look here). When we did find connectors that seemed like they were suitable they were often from large suppliers that only fulfilled orders of hundreds or thousands.

Eventually we found a supplier that has their parts carried by Digi-Key which allowed us to buy individual connectors. The connectors are made by Souriau, this is the catalog we used to order parts. We got a 3-pin connector and 14AWG contacts (which are bought separately from the casing) - specifically we are using the 142G1 series.

142G1 Connector

Instead of having a connector attached to the outside of the body we decided to have a few feet of tether permanently protruding from the submersible. This is because we are not sure how much strain the connectors can take without becoming compromised. Instead the place where the tether enters the submersible is braced with another cord grip as we know that can take a lot of strain.

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