Transformer - Legal or Not?

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busman

busman

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Location
Northern Virginia
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Master Electrician / Electrical Engineer
Can a doorbell transformer be mounted to a metal outlet box (such as a 1900 with a plaster ring for a receptacle) such that the transformer is in the stud cavity. I can't find any code that requires the LV side of the transformer to be accessible. Obviously, this situation is less than ideal, but the only other idea I have is to place a small access door in the sheetrock to access the transformer.

The situation is a house on slab, 2 stories. No closets near the front door. Any great ideas would be appreciated.

Thanks,

Mark
 
I don't have a solution for your problem but I think there is something in the nec that says you can not conceal that transformer connections.
 
The owner had one of these and said it was nothing but trouble. Very unreliable. He is OK with an access panel, I just hate to do this if there is another way.

Thanks,

Mark
 
If the transformer is attached to a 1/2 inch KO in the box, then the wiring contained within the box is accessible. The part that will not be accessible is the transformer itself and its LV wiring. I don't think this code reference covers this.

Thanks,

Mark
 
busman said:
If the transformer is attached to a 1/2 inch KO in the box, then the wiring contained within the box is accessible. The part that will not be accessible is the transformer itself and its LV wiring. I don't think this code reference covers this.

Thanks,

Mark
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If I understood the OP correctly, the stud bay will be covered by drywall. The article says "acessible without removing any part of the building". Drywall would be considered part of the building.
 
450.13 is the reference that requires the transformer to be readily accessible.
Installing the transformer in the box with primary and secondary in the same enclosure violates parts of Art 725.

There are some enclosures designed for this, one that comes to mind is made by WAC. You will most likely need to use their transformer.
 
pierre, You are correct. I wasn't thinking when I wrote it. Primary in the j-box and the seconary is on the outside.
Thanks for reminding me.
Jim
 
In Sunny SW Florida, We mont the transformer on a metal handy box cover exposed in the garage. It is usually mounted up high over the Water Heater or over the panel. In some out of the way place. The Transformer and LV wires are exposed. You cannot mont it is the attic as it says so on the transformer. temperature limitations. A good place I used to put it is in the Dome Ceiling in the kitchen but todays houses have done away with the dome ceilings.
 
WRT 450.13(b), in 450.1 Ex. 4 excludes "Transformers used with Class 2 and Class 3 circuits that compy with Article 725". I can't find a prohibition in 725 that makes this illegal. I can't use the attic because this is the first floor of a 2 story home, with slab on grade. I did see a neat box while searching for similar posts. It was made by Heath/Zenith and was made to mount behind the chime and had separate compartment fo the LV and HV wires. I think this solves my problem if I can find model #119 on the internet.

Thanks,

Mark
 
This is an existing house - so I would like to put the transformer and chime as close to the front door as possible to avoid 'swiss cheesing' the guy's house.

Thanks,

Mark
 
I have used a box for new construction that is made for this purpose. I bet they make a cut in variety. It is roughly 4" square deep box. It has a cover plate that has the transformer mounted to it. The 120V goes into the box, make your connections and then put on the cover. There is a groove in one side for the bell cable. they connect to the LV terminals and the chime mounts over the box covering it completely. UL listed for the purpose and satisfies the code requirements for separating power and low voltage. Also when the transformer goes bad in 10 years or so, all you gotta do is take down the chime and replace it. No hunting for the transformer. Lastly, you have a nice 4" square hole to work through to fish the wires in the wall. The only place I have seen them is lowes. I'll check to find a manufacturer.
 
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