Wiring doorbell transformer in electrical box


Old 12-02-15, 10:35 PM
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Join Date: Dec 2015
Posts: 2
Wiring doorbell transformer in electrical box

Hello -

I am planning on wiring a new doorbell in a house that has never had one previously, and need some help to confirm that my understanding of the wiring is correct. Since there is no pre-existing wiring, and based on the location of the door and inability to run wire up to the attic (no basement), I've determined that the only place to draw the power from is a pre-existing duplex outlet inside my home. The outlet is in a central area and I do not want the transformer to be seen.

My plan is as follows below. I'm trying to do this all to code in SC.

1) Replace the single gang box with a triple gang box. This will allow me to keep the duplex outlet, as required, since it is the only outlet on this wall. It will also allow extra space for the transformer heat to dissipate.

2) My understanding is that the NEC requires the transformer to be accessible, and therefore, I cannot mount it on the side of the box, as it would be behind drywall. Therefore, I plan to mount the transformer inside the box, thus being accessible.

3) I'm aware of the restriction that Class 1 120V power can't be in the same box as the Class 2 low voltage wiring. I would mount the transformer to a divider to keep the duplex outlet & 120V input to the transformer on one side, and the low voltage output on the other.

Am I missing something here? Is my plan appropriate and following code? I know this is not the "typical" doorbell transformer installation... really wish the previous owners had put a transformer in when the did a complete re-wiring and gut job 8 years ago

Appreciate any feedback or help. Thanks
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Old 12-03-15, 09:27 AM
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Is a wireless doorbell out of the question? :-)

It sounds like this would be ok by code. I'm a little concerned the box doesn't provide enough opportunity for heat dissipation, but it's probably ok. The buzz that will inevitably develop in the transformer over time might be really obnoxious in a living room.
Old 12-03-15, 08:49 PM
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Tough installation.... however.... it doesn't address how you'll get the wiring from the transformer to the chime to the button. A wireless doorbell for Christmas.
Old 12-04-15, 06:09 PM
Join Date: Sep 2015
Location: US
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I think this will help solve the least of your problems. Transformer will be secure and required separation for Class 2 wiring is maintained.

593 Mounting Plate
Old 12-05-15, 01:19 PM
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Join Date: Jan 2010
Location: USA
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I think this will help solve the least of your problems. Transformer will be secure and required separation for Class 2 wiring is maintained.

593 Mounting Plate
Interesting, I have never seen one of those. The real issue remains though like PJ brought up, how will the low voltage wiring be routed to the chime and to the button.
Old 12-05-15, 02:10 PM
Join Date: Mar 2007
Posts: 1,341
I went wireless years ago after the wired bell died. It cost less than $30, took less than 15 minutes to install and I have yet to change the batteries.
Old 12-07-15, 08:45 AM
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Join Date: Dec 2015
Posts: 2
Appreciate the replies. When I went into the crawlspace to start routing the bell wire, I found a previously hidden J-box going to my outdoor outlets. Ending up tapping the transformer into that and finished the wiring this weekend.

It was not the most fun project (house is 150 yrs old so crawl only has 12" clearance), but it is done and personally I much prefer over wireless. Thanks.

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