NEC Guidelines – Does Code Allow In-Wall Mounting of Low Voltage Transformers?

low-voltagenec

I am asking if NEC code permits for in-wall (gang box) mounting of low-voltage transformers and power supples, and if so do these product have a name or term?

My use case is low-voltage electronics mounted to drywall: a small car amplifier, an Arduino, Raspberry pi, some 12v LED strips, powering car-type DC accessories. I am looking to hide as much wiring as possible.

I realize you can't dissipate unlimited heat in the wall. 55 watts – the Class 2 limit – comes out to 12v 5.5A if I did the math right and that's easily enough power.

As examples of failed terms I tried: "doorbell transformers 1 gang" and "in-wall Power over Ethernet supply". We've all seen the 4-port USB 1-gang devices – I want that for 12v.

Please do not answer with specific products/links. I am asking if these things EXIST and whether I have been calling them the wrong name. I have already posed this question before but it was deleted over the holidays (reason: "no shopping for links") so to avoid that experience again I need this strongly worded disclaimer. 🙂 Thanks all!

https://diy.stackexchange.com/questions/180414/does-anyone-make-a-12v-in-wall-gangable-power-supply-like-the-usb-ones

Best Answer

You can do this, but you're best off ditching gang-boxes to do so

What you want is a 12VDC NEC Class 2 power supply, listed to UL 508. These are made as more-or-less commodity items, which is the good news. However, since they are mostly used for industrial controls work, they come in a DIN rail module form factor, which doesn't fit well into typical junction boxes. Instead, you're expected to mount them into a NEMA enclosure, as one would use to house an industrial control panel. Fortunately, flush-mountable NEMA 1 enclosures are readily available through your friendly local electrical supply house, or through MRO/industrial controls suppliers online for that matter.

Note that these DIN rail supplies are designed to be used without a barrier; mains comes in one end, and low-voltage DC comes out the other, easily allowing the installation to meet the ÂĽ" rule found in NEC 725.136(D) point 1:

(D) Associated Systems Within Enclosures. Class 2 and Class 3 circuit conductors in compartments, enclosures, device boxes, outlet boxes, or similar fittings shall be permitted to be installed with electric light, power, Class 1, non–power-limited fire alarm, and medium-power network-powered broadband communications circuits where they are introduced solely to connect the equipment connected to Class 2 and Class 3 circuits, and where (1) or (2) applies:

(1) The electric light, power, Class 1, non–power-limited fire alarm, and medium-power network-powered broadband communications circuit conductors are routed to maintain a minimum of 6 mm (0.25 in.) separation from the conductors and cables of Class 2 and Class 3 circuits.

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