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We have an outdoor electrical outlet w/ two knockouts. I was going to add the doorbell transformer in there but I couldn't find out if it is code to have the transformer in a dry outdoor place. It is unlikely to get any rain or snow unless there is a really severe storm and knocks over furniture.

A basic Google search: "can a doorbell transformer be outdoor" yields this from the home depot, really? I've never seen doorbell transformers outside.

"Doorbell transformers are usually located outside the home along the siding or on a wall in the garage. They may also be fixed to a wall in the basement or closet near the front door or entryway. If you don't see it in any of these places, check the walls in the attic. It may be tucked behind the insulation."

Update

thank you for your responses. I didn't see anything in the transformer's documentation about outdoor use.

In the before screenshot, I mounted the transformer for a couple of weeks to at least have a doorbell working. It rained a couple of times, and there was no moisture on it. Still, it looked terrible so I went ahead and used the LiquidTite PVC conduit to feed it under the deck. The transformer I moved to a weatherproof box under the deck, 2 gang. Now it is secure and away from the elements. I even power washed around the setup a few weeks after and no issues.

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    I just went through 4 different brands of doorbell transformers, they all connected to a box with 1/2” knock out for the line voltage but all had exposed low voltage contacts. None of them specified the location. Although low voltage is safe for human contact exposed live terminals 110.27.A would require guarding for 50-1000v. So not specifically disallowed. I would not but I did not see a code reason a normally dry location would not allow this. Your low voltage routing would be the next challenge.
    – Ed Beal
    Mar 5, 2020 at 0:07

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None of the doorbell transformers I have used would be code compliant outside. Your 120v junctions would be fine inside the box but the transformer and low voltage would be exposed. The NEC requires us to install electrical equipment according to its listing 110.3.B. If the transformer is protected and the low voltage and line voltage are separated with barriers it may be possible but normally I would say NO.

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Code doesn't decide that. The UL Listing does.

You must obey the UL listing, which is to say, the labeling and instructions are part of the UL listing. You must follow them.

So if you select a transformer labeled for outdoor use, you are all set. Otherwise no.

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