So I have a nice plastic waterproof box for my first real Arduino project (swimming pool water chemistry monitoring system).
The box will have a power line coming in and several coax cables with BNC connectors on them.
I have various size cable glands but I don't know how to ensure a waterproof entry while using a gland large enough to allow the bnc connectors through.
Anyone have any suggestions for closing up this opening in an easily removable way (so the cables can be easily taken out)?
Hopefully, you have decided to show the most inappropriate for the size of cables used, but I guess it depends on what is already on the other end of the cables, which you don't show. As things are, silicon goo is as good an option as anything else, the gland thereby serving to just provide some depth to the hole.
Waterproofing and removability are not compatible. Waterproofing with cables coming out is nigh impossible short of potting the electronics entirely, and even that is not 100% waterproof.
For always-on projects (mains powered) use an inverted bucket style container. Big opening on the bottom for easy cable work; covered against the rain so water can't come in. The big opening also allows for whatever water does come in to also go back out. The heat of the electronics prevent condensation (a few degrees heating above ambient is enough for this).
What you will learn the hard way is that moisture molecules will travel thrulough almost any material known to man.
Over time moisture will get in.
Save those packets that come in manmany things.
Put one in you device and ckange now and again
Thank you everyone for the great analysis and suggestions.
That is the smallest gland size that will allow for the passage of the BNC connectors.
I looked at bulkhead waterproof BNC connectors and may still go that route. Probably not an issue, but it would mean the addition of another jumper (with a connector on each side) on the inside of the box and the bulkhead connector, with the loss that all involves. And, while the claim is waterproof, plenty of it will still be exposed to the weather, so I have my concerns.
I like the idea of a silicone goo or duct seal. These raise concerns about getting some of the stuff on or in the connectors when removing. Of course, it's not like these wires will need to come out often (or ever), so I may be overthinking it.
Is there a silicone goo that anyone can recommend?
However, all your responses led me to do more research on outdoor waterproof boxes and I now realize that it is far, far, far more complex than I had realized, with issues of moisture molecules in the internal air, pressure differentials between in and out causing passage of moisture molecules, etc.
So, I'll throw in a bag of dessicant and not worry too much trying to make it hermetically sealed.
josephny:
Is there a silicone goo that anyone can recommend?
One that doesn't smell.
The ones that do smell give off acetic acid when curing, which would be bad news for electronics in an enclosed space. Check that is is neutral cure, which I believe gives off alcohol and is virtually odourless.
Another suggestion...
Self amalgamating tape is clean and easy to use, and doesn't stick to anything. It forms a single, soft rubbery lump as it does what its name suggests; it amalgamates in to one piece. If you have a separate gland for each cable, wrap the cable with self amalgamating tape where it goes through so as to make the cable thick enough for the gland to seal to it.
I agree with the previous comments though, you should have the cables coming in the bottom and not try to seal it. I would mount the box so they come up through the bottom and not seal the gland. You could add some kind of barrier or baffle around the box to prevent rain spraying directly on it in a storm.
Glands like this may not be water proof if submerged for long periods . The idea is one cable per gland and the rubber insert clamps down in the cable .
Can you not just submerge the sensors and have the rest of the components somewhere dry ( plant room) .
Beware that electricity and pools do not mix - something like a wall wart power supply may not have the integrity for this sort of application. You need to fully understand this and take professional advice on that aspect.
To my mind this is another no go area for making your own electrical stuff .
The design of your box did not take into account the cables being changed. The solution is to make a removable aluminum panel where all the cables go through. Then just seal the edges of the panel so it can be removed when servicing is necessary. And put the panel on the bottom of your box.
Will all cables need to be changeable? Why? If not, permanently seal those that don't.
If the project was mine, I would use the panel with bulkhead BNC connectors so the inside cables would be as short as necessary and then you can change the outside as often as you want.
