Low voltage transformers in a Wiegmann box?

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Old 09-17-12, 10:38 AM
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Low voltage transformers in a Wiegmann box?

I need to mount a 110V-24V transformer for the ventilation equipment in my garage. I also have a doorbell transformer on the wall in my garage that I'd like to enclose. The doorbell transformer is mounted on the plate covering a 1-gang metal box in the wall. So, I thought I'd accomplish both of these by removing the doorbell transformer from the existing box, mounting a Wiegmann 8x8x4 box over the 1-gang box, and mounting both transformers in the box. Since I have 110V in the box, this should be easy.

Just wondering if you think this is a good idea, and would meet code. I like to do everything to code, or better.

This is the box:
1-Gang Nema 1 Screw Cover Wall-Mount Enclosure-SC080804RC at The Home Depot
 
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Old 09-17-12, 01:05 PM
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The box you linked to doesn't appear to be made for attaching to a 1-gang wall box, and it doesn't appear to be ventilated. Transformers get pretty warm.

Can you mount an extension to the wall box and mount the transformers to that?

BTW, you shouldn't "have 110V in the box." You should have 120V. If you only have 110V, ask your power company to check your service.
 
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Old 09-17-12, 02:59 PM
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Actually I meant to say 120V.

I could remote some of the knock-outs to the Wiegmann box to give it some ventilation, but I suspect that would be a code violation of some sort, since I'd have 120V wiring inside.

I might be able to mount an extension to the existing wall box and mount the transformers to that, but don't know if there would be enough room for both transformers on the cover plate. And, I'd rather that the transformers were enclosed.
 
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Old 09-17-12, 03:34 PM
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Well, this is why I ask before I do stuff. Doing a bit more searching, I see that this is not a great idea. It appears that electrical code does not allow enclosures with both 120V and low voltage wiring inside, which is what I was thinking. Transformers are almost always mounted through a box cover, with the 120VAC connected inside and the low voltage wires connected outside. Apparently this is for heat dissipation and well as maintaining separation of the 120V and low voltage wiring.
 
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Old 09-17-12, 03:56 PM
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Is there such a thing as a 3-gang extension box that will attach over a 1-gang wall box? I've seen the 2-gang extension boxes, but I'm not sure I can fit both transformers on that.
The 1-gang 22.5 cu. in. box:
1-Gang 22.5 cu. in. Square Extension Ring (25-Pack)-187 at The Home Depot
 
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Old 09-17-12, 05:19 PM
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Transformers are almost always mounted through a box cover,
The ones I'm familiar with mount directly to or through a KO in the side of the box. That's why I suggested mounting a 1-gang extension and mounting the xfmrs on that. Covering the x-ring separates the wiring, as you noted.

You can enclose everything in a ventilated box.
 
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Old 09-17-12, 09:18 PM
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Thanks for the tips. I've seen pics of what you are suggesting. I think if I had an extension that was 2 1/8 deep I could mount the xformers on the sides. It might be tricky with a box that's only 1 1/2 inches deep though. I think most of the transformers are about 2" wide in the narrowest dimension.

Can I mount a metal extension on a plastic box?
 
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Old 09-17-12, 09:37 PM
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think if I had an extension that was 2 1/8 deep I could mount the xformers on the sides. It might be tricky with a box that's only 1 1/2 inches deep though. I think most of the transformers are about 2" wide in the narrowest dimension.
You can mount a second X-ring if you need to.

Can I mount a metal extension on a plastic box?
Yes.
 
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Old 09-17-12, 09:46 PM
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Would this work?

Ah, now I think we're getting there.

I could use one of these on the existing 1-gang box:
4 in. Square Box Extension for Switch Boxes 1-1/2 in. Deep Drawn (8) 1/2 in. & (4) 3/4 in. Side KO-187 at The Home Depot

Then, if there isn't enough clearance for the transformers mounted through the KOs on the sides, I could add one of these:
4 in. Square Extension Ring 1-1/2 in. Deep Eight 1/2 in. and Four 3/4 in. Knockouts-8203 at The Home Depot
 
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Old 09-19-12, 08:45 AM
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Rather than stacking 2 extension rings to get the clearance I need, could I use a 1/2" metal elbow to connect the transformer to the first box?
 
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Old 09-19-12, 08:52 AM
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Rather than stacking 2 extension rings to get the clearance I need, could I use a 1/2" metal elbow to connect the transformer to the first box?
The first extension ring?

Possibly. Or an offset nipple. What do you mean by a 1/2" metal elbow?

And what do your xfmrs look like? Can you post a picture of each, showing its mounting point and primary wires?
 
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Old 09-19-12, 08:55 AM
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I could use one of these on the existing 1-gang box:
4 in. Square Box Extension for Switch Boxes 1-1/2 in. Deep Drawn (8) 1/2 in. & (4) 3/4 in. Side KO-187 at The Home Depot

Then, if there isn't enough clearance for the transformers mounted through the KOs on the sides, I could add one of these:
4 in. Square Extension Ring 1-1/2 in. Deep Eight 1/2 in. and Four 3/4 in. Knockouts-8203 at The Home Depot
You could, but why? What do you gain over using a single-gang extension ring?
 
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Old 09-19-12, 09:15 AM
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I currently have a single gang box in the wall, with the doorbell transformer mounted in the cover. I need to add another transformer for my HVAC ventilation equipment. I could put it inside the furnace cabinet, but I'd rather not do that.

If I put the RACO 187 extension ring on the existing in-wall box, there isn't enough clearance to mount a transformer in a KO on the side, so I could still only put one transformer through the cover.

So, if used the RACO 187 extension ring with another 2-gang extension ring stacked on that, it would give me the clearance to mount both transformers on the sides of the second extension. That would be an acceptable solution, but I'd rather avoid stacking if I can.

I have a "standard" doorbell transformer, with a 1/2" threaded mount. It's about 2 x 2.25 x 2.5 in size. I don't have the HVAC transformer yet, but I need at least a 40VA for that. I could put in a different doorbell transformer too, it it works better.

I was just guessing about the 1/2" elbow. An offset nipple would do it, and then I could get both transformers on the sides of the RACO 187 extension. I'd have to use one on each transformer.
 
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Old 09-19-12, 09:18 AM
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Also, if I used the offsets on both transformers, I could probably just put a single-gang extension on the existing in-wall box.
 
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Old 09-19-12, 09:34 AM
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Or, if I use only a single-gang extension ring, I could mount one transformer through the cover and one in a KO on the side, using an offset like this:
1/2 in. EMT-to-Box Offset Set-Screw Connector-90371 at The Home Depot
 
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Old 09-19-12, 10:29 AM
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There's an EMT connector on the end of that offset nipple. How will that connect to your transformer?

if I use only a single-gang extension ring, I could mount one transformer through the cover and one in a KO on the side,
Why punch a hole in a perfectly good cover, and increase the depth needed in the vented box?

I have a "standard" doorbell transformer, with a 1/2" threaded mount. It's about 2 x 2.25 x 2.5 in size.
That sounds like something that would mount on the side of a standard box or a standard x-ring.

I need to add another transformer for my HVAC ventilation equipment. I could put it inside the furnace cabinet, but I'd rather not do that.
Why not? Isn't that the first place a service tech would look for it? How will s/he know it's on the wall in the garage, hidden inside a ventilated box?
 
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Old 09-19-12, 11:40 AM
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Rather than the offset nipple with the EMT connector, I could use a regular offset nipple with a threaded coupler. If the wire leads are long enough that should work fine.

I had actually given up on the idea of the ventilated box. I was just going to mount one in a KO on the extension ring, and one in the hole on the cover.

As far as putting the extra transformer in the furnace, I could, but it involves connecting into the 120VAC wiring in the furnace which I'd rather avoid if possible (you know, for the warranty and such).
 
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Old 09-21-12, 03:58 PM
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OK, I think I have a good solution, and one that's much simpler. I'm not using the ventilated box. I'm just going to mount the transformers on the side of the extension ring.

I'm going to use this extension ring:
4 in. Square Box Extension for Switch Boxes 1-1/2 in. Deep Drawn (8) 1/2 in. & (4) 3/4 in. Side KO-187 at The Home Depot

Now, that's a 1.5 inch deep box, and will not provide enough clearance (to the wall) for mounting the transformers on the side. So, to get the clearance I need, I'm going to stack 2 of these behind the box:
Wall Box 1 Gang Extension Ring 1.0 Cu. In. at Menards

Stacking two of those will move the extension ring 1/2 inch out from the wall, which will be just about perfect.
 
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