Running 12V DC through pre-existing 110V intended wire?

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My under-cabinet fluorescent lights which came with the house are beginning to fail, and I simply don't like them. Currently these lights are one on each side of the sink. They are run such that power goes into the first light (on the left side of the sink), then up and through the wall above the sink, and finally back down and into the second light (on the right side of the sink). It looks to be a 16/3 Romex wire.

I want to replace these fluorescents with LED Strips. What I'm trying to decide on is how to provide power to the new LED strip lights on each side of the sink, without getting into the walls or running any conduit. It's not necessarily as easy as it sounds since the LED's are running on 12V DC.

I'll definitely be installing a switch and a transformer on the left side of the sink, and it will be simple to power the LED strip also on the left side from it. But as for powering the LED strip on the right - can I use the existing 16/3 Romex in the wall to carry that 12V DC power to the new LED strip on the right side? (Note that all this wire does right now is connect the pair of existing fluorescents on each side of the sink, it is *not* connected to any other 110 fixtures or outlets or anything else).

The upside is that I use only 1 transformer. The downside is that while the 110VAC rated wire can easily handle the 12VDC, it's is most likely not "right"? It doesn't seem to cause any harm by being bigger then needed (unless it causes a huge voltage drop but I doubt it will). But it seems that because this wire is normally used for carrying 110V power, someone else down the road might try to use it as such if they don't understand it's actual function? I don't want to totally screw up someone else someday (especially in an unsafe manner) if I can avoid it. It seems my other options are to either get into the wall or run conduit (which I don't want to do), or to leave the 110V wire carrying 110V, and then just stick a 2nd transformer on the right side of the sink as well which is a waste but it would at least be easy to understand.

Not sure which way to go, anyone reading this far and have an opinion?

 

[skyking]

Use the ac wiring and switch for AC power as intended. use two transformers.

 

[tracerbullet]

My gut feel is that is the correct way to do it. But I'm curious why that's what you recommend? Legally correct, most straightforward for someone else, an immediate safety issue I haven't thought of, something else?

 

[Toastedlightly]

IANA(Electrical Engineer), but look at an allowed ampacity table:

http://sparkyjohn.com/ampacity/ampacity.pdf (18 gauge isn't listed here)
http://www.stayonline.com/reference-circuit-ampacity.aspx (lists 18 gauge)

The ampacity is rated at 10 amps. I don't recall all the de-rating that occurs (you lose rating for being in walls, being in a romex cable), but I think it comes out to 75% rating. So you have 7.5 amps available current. At 12VDC, you will be able to have 90W available. Do you have the rating of the wire?

Below applies to 120v
Also, if you do have a 16/2 wire, you'll want to make sure you have a 10 amp (maybe 7.5 amp) circuit breaker. Check with an electrician on that. If you don't, the circuit isn't properly protected.

IANA(EE), so take whatever I say with a grain of salt.

 

[Greenman]

I doubt you have 16/3 wiring right now, 14/2 would be my guess, the ground wire doesn't count. I would say to go ahead and use it as long as doesn't enter a j box containing 120v wiring.

 

[DrPizza]

It sounds reasonable to me. 16/3 Romex?! Egads, some builder was really trying to shave a few cents off the cost of building your home.

I checked the Mike Holt forums; seems it's allowable, provided you terminate in a junction box, which is appears you would be doing. http://forums.mikeholt.com/showthread.php?t=115729

However, I'm not exactly sure what you're doing on the transformer side - as far as I'm aware, a single junction box cannot have both low voltage and household voltage in the same box (though there are split boxes where one side is one and the other side the other, with a barrier in the center). Thus, I don't know exactly what code says to do where the transformer is - I could look it up, but I'll let you search. The Mike Holt site and forums provide a wealth of good information. I've never installed a low voltage circuit before (though did replace a door bell transformer once - but at that time, I never looked at code to see if I should update the circuit.)

 

[LTC8K6]

Put a tag on it, identifying what you did, so that future electricians will have a clue. :biggrin:

 

[piasabird]

Wonder if you can just get a kit like they use for yard lighting?
Typically they have a step down adapter of some kind and it can supply current for 6-12 lights.

 

[tracerbullet]

I am using Romex as a generic term, that might not actually be it. But I am sure it's 16 gauge, I wish the house had been wired with more but that's what is in this particular spot. The 16/2 vs. 16/3 I may have used incorrectly too. It's 3 wire though - black, white, bare copper.

And yes to reiterate the wire in question that goes up and over the window (in front of the sink) and back down connects the 2 existing lights only, nothing more. It goes into the wall on the left side, and out of the wall on the right side. In both cases the terminations of it are inside the existing fluorescent fixtures.

I'm planning to use parts from this site: http://www.inspiredled.com/ , specifically:

* Dimmer switch in wall: http://www.inspiredled.com/lutron-wall-dimmer-2455
* Into a transformer: http://www.inspiredled.com/e-series-transformer
* Interconnects as needed possibly including Y cables (TBD depending on this post): http://www.inspiredled.com/custom-interconnect-cable
* 2 lights of this style, in 48" lengths: http://www.inspiredled.com/products...-covers/pro-series-21/pro-series-21-led-panel

I'm now leaning towards using the existing wire that's in the wall, with some sort of small covered junction box on each side, stuck to the underside of the actual cabinets, where I can make connections to it and hide wire nuts.

The transformer box would be the only place that any "actual" 110V AC and 12V DC would ever meet, and it is designed for it. The other junction boxes which I might add, as mentioned above, would contain 2 types of wires but only be carrying 12V DC throughout.

 

[Greenman]

It sounds reasonable to me. 16/3 Romex?! Egads, some builder was really trying to shave a few cents off the cost of building your home.

I checked the Mike Holt forums; seems it's allowable, provided you terminate in a junction box, which is appears you would be doing. http://forums.mikeholt.com/showthread.php?t=115729

However, I'm not exactly sure what you're doing on the transformer side - as far as I'm aware, a single junction box cannot have both low voltage and household voltage in the same box (though there are split boxes where one side is one and the other side the other, with a barrier in the center). Thus, I don't know exactly what code says to do where the transformer is - I could look it up, but I'll let you search. The Mike Holt site and forums provide a wealth of good information. I've never installed a low voltage circuit before (though did replace a door bell transformer once - but at that time, I never looked at code to see if I should update the circuit.)

Generally the transformer mounts on to the junction box and the LV connections are on the exposed side of the transformer. The LV cable never enters the box. Around here, the inspectors won't even look at LV wiring, they don't care what you do with it.

 

[SparkyJJO]

I doubt it is 16 awg as that was never used for in-wall wiring for circuits anywhere.

 

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I doubt it is 16 awg as that was never used for in-wall wiring for circuits anywhere.

You are right, I looked again and it is indeed 14 gauge. Sorry.

 

[herm0016]

as long as you label everything clearly. I would use the existing wiring. no reason not to, and those led lights will not take much current.

 

[tracerbullet]

That is my current plan, in fact I have only just now ordered everything I need from the lighting co's website - the transformer, light strips, etc. All I need now is 2 junction boxes which I will make my connections for the existing 14 gauge wiring in - one under each cabinet on each side of the sink. I'll write on the boxes and / or put some info on a piece of paper and keep it inside "just in case" someone else gets into it someday. Or I live there so long I've forgotten about it myself!

Thank you everyone -

 

[Kenny903]

Hi,

I currently have a LED strip light wired up in a dark stairway - it is powered by a 5amp rectifier (Supply A) . the current power supply is on a timer that turns on at night only.

I want to supply a second power source (Supply B) to the LED strip in the stair way so I can use with a manual switch so I can turn the light on during the day.

What I need to know is will this product be ok to make the first power supply a one way supply only? - ( A ) the reason I want to block the power is to prevent other strip lights turning on from that 5 amp rectifier (A).


Finally - will the LED strip light be affected if both power supplies happened to be on at the same time - so if supply (A) was on and supply (B) happened to be left on the LED strip would receive 10amps - would this cause damage?
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