Electrical Question: LED Lighting

Hello Dopers

I hope you’ll allow me to call on your vast knowledge yet again.

I am looking to install some LED accent lighting, and I purchased a setup from the Homeless Despot . I want to make sure that the instructions it includes are kosher from a code and safety perspective.

The kit includes a 12v power brick. The brick does not include a cord and plug. Rather, it has two terminals (and a ground) and the deal is that you go through a knock out and bring romex from the box to the two terminals. There is a cover for the terminals, so once assembled they are not exposed.

The power brick then gets screwed to the nearest convenient location, which in this case will be an exposed joist in the attic. From it low voltage wires run to the blinky bits.

Does this all seem kosher? I just want to be sure, mostly about having the brick just sitting on a joist (should be OK?) and then confirm that the 12v leads don’t need boxes and such, and can just be fished through the walls as needed.


Can you provide a link w/ pics of the setup?

It sounds right, as long as, from a code perspective, you’re okay to use romex in the location that you’re planning to use it and you staple it at the correct spacing, use a tension relief, it’s properly grounded etc…you’d have to be more specific about what you’re concerned about.

Also, it should be noted that in most cases that directions that come with the item actually over rule (kinda, more like fill in the gaps) of the NEC.

Having said all that, running romex into a small steel box that ‘feels’ sort of external to the rest of the fixture is extremely common. Just make sure you use a proper romex clamp/strain relief so the wires can’t get pulled off the terminals.

Generally, everything up to the termination of 120VAC wiring has to follow code and common sense safety, while low-voltage wiring needs only a little common sense to keep it safe. If putting the brick inside a terminal box makes you feel better and assure that the wiring is safely terminated and protected, do so. For the 12V stuff, just avoid pinch and rub points that might short it out. (I assume the brick has overload protection, but if not, a short could create a minor fire hazard.)

I just did this in my kitchen. LED strips under the cabinets, and LED pot lights in the ceiling. and what you’ve described is correct. As Amateur Barbarian points out, it’s the 120V AC that needs attention to detail.

Should be fine, but I’m saying that without knowledge of your local codes.

The brick may need a local disconnect, possibly current protection.

I would get a box to put the brick in. Get a box big enough to include a switch and a fuse or a set of fuses. Size the fuses to the brick.

Wire from the existing box to your new box have the power go to the switch and from the switch to a fuse and from the fuse to the brick. And from the brick to another fuse then to your LED lights.

Done this way if the brick fails the fuse will keep the brick from leaking too much smoke. Or if one light fails of there is a wiring problem on the low voltage side the smoke will not leak out of the brick. And if you ever need to work on your lights or modify any connection you can without having to turn off the whole circuit.

It sounds like the same setup as used for recessed lighting, bathroom fans, etc. They all have a metal box attached with a snap off cover. You bring the Romex in the hole you choose, hook up to the fixture wiring and put the cover on. Done.


If the driver isnt designed to go in a box it might have heat issues, resulting in premature failure. Especially in an attic.

Alot of these things have built in secondary protection that requires power cycling ghe primary to reset.

Thanks everyone! lots of great info. And good point about the heat in the attic- in fact I wouldn’t be surprised if that’s what kills it down the line. I wonder if I should have a spare brick on hand in case this one goes…

Spares wouldnt hurt if they’re not to exspensive. Depending on manufacturer, product line and the phase of the moon it’s kind of a crap shoot whether replacement parts will be available at any given point in the future.

Youbetcha! If the device manufacturer does not specifically say to do something (like enclosing the power supply in a box) don’t do it. The NEC has specific language concerning its deferral to manufacture’s instructions, so don’t get clever trying to second guess these instructions. There is a reason for them…* They attempt to prevent amateur electricians from using their imagination*… And thereby creating an unsafe condition, as indicated below.

I would add: Beyond premature failure, there is an increased opportunity for fire.

As the lighting that I installed was for the kitchen, I installed my transformer in one of the cabinets - on the top shelf on the back wall. It can’t be seen, it doesn’t take up much room, and is a much cooler environment than in the attic.
I didn’t do that for cooling, however. It was just easier that way.
You wouldn’t have any problem with what you described: attached to one of the joists in the attic. Just keep insulation away from the transformer.

The “you” referred to as not having “any problem with what you describe” is ambiguous. That, combined with your previous agreement with Amateur Barbarian concerning enclosing the power supply in a box; is just inherantely wrong… So I am forced to disagree with your position.

Oldolds, do you have a part number for the power supply in question?

Read again. I didn’t advocate installing the power supply in a box, though I missed Amateur Barbarian advocating it.

I’m guessing since Romex is brought to the brick it counts as a junction box and needs to be mounted someplace where permanently accessible. You’d want it to be anyway so you you aren’t ripping up drywall if it ever goes bad.

It’s hard to talk about code and even harder to debate it when we don’t know what we’re talking about. OldOlds, it would be really helpful if you’d provide a link to the product you purchased. I think most of us, or at least myself, hear 12v and brick and picture a plastic wall wart style box. But when you mention a knockout, I’m thinking it’s a metallic enclosure. Mounting a metallic junction box in an attic (following all local codes) is fine and from there, as was said earlier, code on low voltage wiring is fairly lax. However, the NEC is available on the internet and while little changes from one version to the next, make sure to look at the one that your state has currently adopted and if you really want to go overboard, check your state and city laws as well, though I really doubt they address low voltage wiring.
OTOH, I spend a fairly good amount of time, for a non-electrician, reading the NEC, and you’ll drive yourself batty doing it. If you just need to replace one light, sometimes it’s easier to just replace the one light.

To go back to the OP, however, if the item has a UL stamp on it and includes something along the lines ‘always follow all national and local electrical codes’ (and keep in mind that the national electrical code says to follow the instialltion instructions), you’re good. But, yeah, run the romex to the box, properly connect it and it sounds, at least from here, fine.

So, A)Can you link to it and B)What, specifically, concerns you?

Also, I’m guessing this is a recessed light, right? That’s why there’s no cord and plug, they don’t want homeowners installing outlets in their attic or walls or running extension cords up to lightbulb sockets in their attic. If it is recessed there’s no reason to have a cord and plug. If it’s not you can probably buy cord and plug kit for it (or make one).

FTR, I’m picturing something like this, which is very common for recessed lighting (even regular 120v lights where there just isn’t a lot of space). In fact, I only managed to fine one picture of a setup where the transformer was totally exposed, but it was on an international website and clearly for worldwide distribution (based on the input voltage)*, if the OP has that one, I’d have some suggestions for how to put it in a box, I’ve done similar things with relays that wouldn’t otherwise have any protection.

*Also, sometimes those are meant as retrofits and the entire thing is supposed to fit inside the old can, which acts as a junction box.

In the meantime, here’s some more detail:
-It actually does include a cord & plug, but this can be removed so that romex can be attached in its place. It’s nor a wall wart, but a rectangle with two mounting holes. About the dimensions of a typical laptop power supply. One end has terminals to connect the 120VAC and the other end outputs 12v.
The power in this case would be coming off a standard new work box that already exists to power a ceiling light. That would have the accent lighting switched on the main room light. The LED setup includes a little remote so that it can be adjusted (color, on/off, brightness) independently, but only if the main switch is on. This is desired in the application, as the LEDs will automatically come on when the room light is turned on, and can be offed if desired. I have bench wired it and all seems to operate as promised. Lest someone ask, the remote receiving unit is wired into the LED strips in the room, so no, the signal does not have to make it to the attic.
My main reason for posting was that the brick has to live somewhere, and is absolutely not intended to go in a box. So the wiring would be like so: [box]—(romex)—[brick]-----12v where the brick is mounted to an exposed joist.

I will get the actual info when I get home, but is similar (not actually) this one. As I mentioned, though, the instructions in the unit I have specifically state to remove the cover, remove the cord&plug, and wire romex to the terminals for the application I am using and in fact on the bench this worked exactly as written (that is, everything lined up and connected properly, the cover went back on as it should, etc). The link below appears to show two outputs on the 12v side, whereas mine has only the wires to drive the LEDs