I'm in Maryland, US.

I was hoping to wire from the switch:


to this:


I would like my shower heated mirror to come on when I turn on the exhaust fan. Some other models of the exhaust fan recommend not wiring up other devices. But I'm hoping it's possible because A) the same recommendation is not mentioned in this model and B) the heated mirror is low voltage.

Is there any problems with this?

EDIT: now it seems like the main issue will be pluging in the mirror transformer to code. Is it against code to put an access panel to access an outlet either in the ceiling or in a wall? This is how they seem to be doing it in their video:


Planned steps:

  1. wire existing 12/2 romex to exhaust fan (original leg to old exhaust fan) via pig tails and secure in recessed junction box secured to ceiling joist
  2. connect 12/2 romex from this junction box to outlet which will be b̶e̶h̶i̶n̶d̶ ̶t̶h̶e̶ ̶d̶r̶y̶w̶a̶l̶l̶ (see edit above)
  3. secure plug-in power supply from heated mirror into this outlet

If there are any issues, NEC considerations, or any other relevant information, any information would be GREATLY appreciated. Thanks!

enter image description here


1 Answer 1


You can have a removable access panel to mount the transformer in the wall if it is rated for being enclosed. Some transformers are not listed for being enclosed. Most transformers similar to this are mounted on a junction box with the 120v inside and the low voltage on the outside in this case a full wave bridge may be integrated in the transformer or connected to it and the 24vdc is taken to the mirror for the heat and light.

I make “picture frame” access panels I have always used Velcro to hold them in place. An inspector did recommend screws as they are allowed. Removable panels designed for access that do not damage the finish are code compliant. So if the transformer is allowed in a stud bay you could create a “picture frame” attached to the Sheetrock but the frame covers the seam. Velcro or screws can be used to hold this in place.

  • Thanks for the reply Ed. So upon further research, and my reading of NEC 314.29 and the definition of 'accessible', it sounds like my outlet can be covered by an access panel (not being a part of the building that has to destroyed for access) . I'm ASSUMING that the transformer (class 2) was meant to be put behind a wall as this is what is done in the manufactures video by the manufacturer. Do you know of any way of telling for sure? im attaching a pic of the transformer.
    – Joe
    Commented Sep 20, 2020 at 17:19
  • A plug in transformer will not be listed for being enclosed and would be questionable for a permanent install in my opinion, however if the MFG states to do it that way it would meet code. Yes it can be inside the wall as long as the panel is designed for access and the finish is not affected. 40va is the size of a normal doorbell transformer , I would use one of these as that would be code compliant , mains power inside the box and low voltage on the outside , I expected it to be DC but the photo shows ac so I would go that route and it would be code compliant and last much longer than a plug
    – Ed Beal
    Commented Sep 20, 2020 at 19:03
  • Thanks for your time Ed. I'm just reluctant to replace the transformer because 1) the manufacturer says to not exchange the transformer in the manual and 2) I'm such a novice at this stuff. Do you have any suggestions on how I might go about looking for a better replacement?
    – Joe
    Commented Sep 20, 2020 at 23:17
  • Transformers are transformers as long as it is the same voltage and at least 40va (larger va is ok) it would be ok I mention door bell transformers because many of these are designed to be mounted on an electrical box so the mains voltage is separated from the low voltage. Some inspectors will flag a permanent installed plug in like this but it is allowed as the listing instructions state to use it. The only issue that I see is it being enclosed.
    – Ed Beal
    Commented Sep 20, 2020 at 23:37
  • So I should say that the manual doens't offically state that it should be installed behind an access panel. It does say "Transformer must be accessible and must have air flow. Never put a transformer or outlet In a closed wall." And by 'closed wall' I assume they mean rocked in. Since an access panel wouldn't be closed, code seems to allow this, I'm assuming it's the company's recommendation. The only mention of 'access panel' comes from their install video, not their manual. I'm still waiting to hear back from them by email.
    – Joe
    Commented Sep 21, 2020 at 0:29

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