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I spliced 120V AC wires coming to the lamp so that I would have electricity for the USB adapter that would power USB camera (USB is used only to power the camera. The actual data transfer happens over WiFi). I put the USB adapter behind the black metal thing that attaches lamp to the wall.

Camera Installation (with imitated USB cable)

While everything is under the roof and should not directly get in touch with water I still had this "awesome" idea to wrap the USB adapter into a plastic bag "just-in-case" water would somehow get there. However, now I am having second thought about this awesome idea because I am afraid that the plastic bag could actually facilitate condensate to form on the adapter and possibly damage it.

  1. How worried I should be about using plastic wrap around the USB adapter (note, that this is dry California)? Would plastic wrap actually allow condensate to form and possibly cause short in USB adapter?
  2. The USB adapter had a warning notice that explicitly mentioned that it is intended to be used only indoors. Just to be on the safe side, should I be worried about using indoor electronics in the way I did under the roof? Why?

The plug of USB adapter

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  • You should really put put an indoor electrical box with a proper outlet on the inside of the building that can accommodate the camera power supply. Then low voltage wires can be routed through the wall in a manner compatible with the building construction to power the camera. Low voltage things should not really be inside the electrical box enclosure with mains voltage wiring.
    – Michael Karas
    Dec 27 '15 at 8:35
  • Almost all USB power adapters that I know about have AC plug terminals designed to go into an electrical outlet. I wonder how you managed to connect the AC wire taps to the USB adapter.
    – Michael Karas
    Dec 27 '15 at 8:37
  • @MichaelKaras I think that's an excellent question--are the 120V "hot" and "neutral" just spliced directly to the prongs on the adapter somehow? Dec 27 '15 at 20:38
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    The problem Jonny is going to have with putting the transformer in a box inside is that USB plug ends require bigger holes to pull through walls than bare un-terminated cable, and most home DIYers aren't equipped to terminate USB cable themselves. It would be better to use a PoE camera and Cat5e cable. Dec 27 '15 at 20:40
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    That "splice" is a disaster waiting to happen, as is stuffing a transformer into the back of another fixture that it wasn't intended for. I'd just get suitable equipment for your application.
    – Comintern
    Dec 28 '15 at 2:01
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  1. You say the adapter is behind the light shroud. I wouldn't be worried about that part. Besides you will have to poke a hole in the plastic bag for the plug and the cable thereby making it no longer moisture proof. Adapters and cables are fairly cheap and it should last for a while depending on your weather.

  2. If the adapter itself shorts internally (which is not likely considering where you put it, and the fact that it is sealed) it could trip your breaker but probably won't draw enough current to melt or cause a fire.

I would be more concerned with the cable to the camera and having moisture (maybe fog?) condense on the cable and drip into the camera. If you can rotate the camera and have the cable enter from the bottom then any moisture will drip off the cable before it gets to the connection with the camera.

Good Luck!

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Don't Use a Bag...

I wouldn't wrap this in a plastic bag at all. That will probably cause condensation to accumulate inside the bag and dramatically increase the chances of moisture dripping inside equipment where it will do harm.

I would instead look into waterproof connections. The cable itself won't be harmed by a little moisture, but water could enter sensitive equipment wherever cables plug in. For example, there are companies that let you specify your own waterproof USB cables. Or, make all of the connections, then seal around the edges of the connections with silicone.

The other answer (@ArchonOSX) makes a good point about rotating the camera so that condensation drips away from the equipment. Additionally; I would suggest making sure there is a downward loop in the data cable so that water runs along the cable to the lowest point in the loop then drips harmlessly off of the wire insulation.

Electrical Code Violation

But, I actually see at least a couple of big issues with this. I don't have the time to look up the specific electrical code around this, but probably article 725 presuming the U.S. NEC.

The USB power cable surely qualifies as a Class 2 or Class 3 low voltage circuit, and as such the electrical code prohibits you from installing it in the same box with a 120V supply circuit without using a permanent physical barrier, and so on. The code is the code and doesn't need me to justify it here, but one of the reasons is that there's always a chance of a short putting 120V on the low-voltage conductors, which could fry equipment or present a lethal shock hazard.

Another thing is that splicing 120V leads directly onto the blades of the transformer plug is not acceptable. The only acceptable way to do that would be to make a solid connection to an approved NEMA 1-15 female connector so that you could plug the transformer into it in the normal way.

Appropriate Equipment

Can you replace that camera with an actual weatherproof unit that supports Power over Ethernet (PoE)? It's easier to pull Cat5e (or Cat6 or better) cable through walls and terminate it yourself, than it is to pull USB plug ends through walls, and you may not have the equipment or expertise to terminate USB cables yourself. But with a PoE camera, especially if it has a weatherproof recess on the bottom for the RJ45 port, you can run it from a PoE switch or PoE injector inside the house, or in the attic where it's still protected from the elements.

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  • Sorry, I did not specify it in my question that USB is only used to power camera. Actual Data Transfer happens over WiFi. However, yes, If I would have to pull cables through wall then PoE would make complete sense. However, here I simply spliced wires from already installed outside lighting.
    – Jonny
    Dec 27 '15 at 22:06

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