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I'm looking at installing some security cameras at my place. I have an outdoor outlet that is ideally positioned to power one of the security cameras, however, using a test to figure out if it was working, I noticed that the polarity is reversed.

It seems to be reversed at the outlet, but I tried pulling it out of the receptacle box a little bit to see and the old romex and the freezing temperatures outside make it very hard to work with and attempt to fix for the moment.

Doing some research, I learned that there is a potential danger for appliances with a power switch, because on could be off and vice versa. In my case though, all I need to plug in for the camera is a pretty standard 5v USB AC/DC power adapter. Is there any risk to humans or the cameras in this scenario?

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    appliances with a power switch, because on could be off and vice versa ... no, with reversed wiring, the power switch controls the neutral, which means that the appliance has hot connected at all times
    – jsotola
    Dec 20, 2021 at 15:40
  • What makes you think the polarity is reversed? That 3-light tester is wrong. Dec 20, 2021 at 17:30

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"Polarity" with AC is not nearly the same issues as with DC. It has no effect on the equipment, at all, except when grounding comes into play. The third pin - ground - is connected to neutral at the main panel, so reversing hot and neutral will result in hot-to-ground showing 0V (instead of 120V) and neutral-to-ground showing 120V (instead of 0V). This has major ramifications if you have a short inside a device that then sends power to ground.

However, a standard USB power adapter does not connect to the ground pin. As a result, the device (both the power adapter and the camera that it is powering in this instance) will never see anything different from a proper installation. A human touching the camera will also never see anything different as any failure scenario will not involve the ground pin. In addition, the camera (and any human touching it) is protected from 120V - i.e., unless the adapter fails in a particular (hard to imagine but nothing is impossible...) manner, the only voltage present is 5V DC.

As far as fixing the problem, which doesn't have any real impact right now, the problem could be this receptacle or it could actually be at the previous receptacle or junction box in the chain. (When I was replacing receptacles in my basement recently I found two reversals - so the first receptacle was reversed and the second one was correct!)

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I'm assuming your camera has a plastic wall-wart AC/DC power supply.

Some power supplies bond the negative side of the DC circuit to ground. If the PSU has a third pin (ground) it is possible it's used that way and then polarity matters.

You said it's a "standard" USB style PSU, those usually do not have a ground pin so it shouldn't matter, and in fact usually they don't even have polarized pins so it cannot possibly make a difference.

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