MR-16 puck lights

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sparky_magoo

sparky_magoo

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I went on a service call to a house last Friday. None of the twenty-two MR-16 "puck lights" installed in the cabinets worked. I found five burnt out x-frmrs in the attic. Each x-frmr was over-loaded. I ordered correctly sized x-frmrs. No problem. What disturbs me is each of the pucks has an 18/2 bell wire home run to the x-frmr. I have always used 12 AWG cable for low voltage lights. What code violation could I site to justify tearing out the bell wire & doing it right? This house was wired by my company about two years ago by some one, I have never met, who is long gone.
 
50 watt lamps @ 12 VAC = 4.17 amp load. My concern is the bell wire insulation is grossly inadequate for anything but a door bell load. I have always used 12/2 Malibu cable for similar installations. The wire runs are all under 50'. The owners aren't going to care about the voltage drop to LV lights on a two year old installation. I'm wondering if there is a code violation in using the bell wire to power lights.
 
Doorbell wire is a Class 2 cable. You can only use it, properly sized per amperage, if you have a class 2 power supply. MOST LV transformers are NOT a class 2 supply. Therefore, you have to use a Chapter 3 wiring method (Malibu cable is not a Ch3 method). Romex, MC, and pipe and wire are examples of a Ch 3 method.

If you want to use a class 2 transformer, you are limited to 60W/circuit at 12V (i.e. 5 amps), a class 2 unit will have segregated 120V and 12V compartments, and there will be a number of 5A or less breakers in it, one for each run. See:
http://www.q-tran.com/pdf/QT_Catalog.pdf <----see page 14

For an overview of LV lighting wiring requirements and practices: http://www.q-tran.com/pdf/QT.pdf

I'm in no way connected with Q-Tran, but I do like their products and their literature.
 
If the transformer is Class 2, it shouldn't be a problem, I don't think, but I'm not sure.

I'd recommend looking through the Low Voltage area of the forum, which I've linked to in order of posts. The second one on the list is a good one by Ryan Jackson, which opened my eyes to how dangerous this stuff can be.

I have wired LV lights with 18-2 doorbell wire before, but after seeing Ryan's piece, I had second thoughts.
 
georgestolz said:
Really? Most I've come across have been, since I started looking.
Click to expand...

I don't think I have ever installed one that was class two.

All the ones I can think of where 300 watt (25 amp) output.

Requiring a minimum of 10 AWG but often larger for voltage drop.
 
George,
Unless there is seperation of HV and LV, it can't begin to be Class 2. Most of the units I run across are relabeled buck/boost units, with a circuit breaker supplied.

What brand of units are you looking at? I'd love to have more Class 2 options, but as far as I know, Q-Tran and Semper Fi seem to be the only that will do it, and it's usually a special option. I use a lot of Class 2 for low wattage strip lighting, from companies like Tivoli or Celestial Lighting. ALso, most of the fott lighting you see in the movie theater is class 2.

IMO, in the wrong hands, LV lighting can be more dangerous that 120V work. LV lighting has 5-10 times as much current than HV for a given wattage. Voltage kills, but current starts fires!

mike
 
I ordered 300 watt transformers to replace the smaller ones which burnt up. The transformers are made by WAC Lighting. I am looking at one of the failed originals right now. It doesn't state class 2 or 3. It doesn't even say UL listed. It does say made in China. I ordered the replacement transformers from C.E.D.
 
I suspect my company did install the LV lights. I definitely have class 2 transformers and now will be installing larger ones. I see the bell wire as a serious hazzard. It will be a major PITA to get new wire to the kitchen cabinets. I wonder if the company owners will have the integrity to correct the installation.
 
The Article for reference is usually Art 411.

If you are going to go ahead and use a class 2 Type of wiring method, I advise you to read Mark Ode's article at the UL website before installing this type of wiring method. You will see at 411.4(A)(2) that you will need to refer to 725.52, then to 725.41. There is an FPN that refers you to table 11(A) in Chapter 9. You will immediately notice that this table will take the average reader a long time to understand, if you understand it at all.
Also you will need to read all of the installation instructions for the applicable manufacturers, as they are not all the same, and you may be surprised by what some instruct for the installation.
The above is for the 2005 NEC. If you are referencing any NEC before the 2005, than a chapter 3 wiring method is basically your only choice for a wiring method.
 
Sparkymagoo,
i don't see how you could have Class 2 units if they are in fact rated 300W. Unless they have individually fused/breakered secondaries (5A @12V), you have a class 1 unit. Also, regardless of your type of unit, you cannot exceed the ampacity of your wiring. If you have 50W lights, A=W/V=50/12=4.17A

What transformers are on the way? I don't see any class 2 rated 300W units at the WAC website, just a 60W electronic unit.
 
Betcha locating that transformer in the attic had more to do with its failure than the connected load. I know many such transformers state in their instructions "Do not locate in attic" or similar such wording.
 
mhulbert said:
What brand of units are you looking at? I'd love to have more Class 2 options...
Click to expand...
Well, I was (mis-)installing some puck lights by American Lighting, but I have to confess, I was forced to install them contrary to their listing. I made myself feel better at the time by noting that they were Class 2.

Essentially, what I did was cut the cord, and install the transformer in a junction box. We installed 14-2 NM between the transformer and the light, but those had been installed in prior houses with 18-2 Bell wire.

The pucks I installed were designed to be cord-and-plug connected to the transformer, with exposed cord between the two. They were designed for undercabinets, not concealed wiring as we did.

Hopefully, it will work out. That is just the kind of crap I was getting away from by changing fields. :(
 
This house is located in an area where we had over two straight weeks of 100+ degree weather. I don't know the part # of the replacements. They are supposed to be 12VAC 300 watt output electronic transformers. Maybe I should go with 22 60 watt transformers.
 
I was mistaken. I didn't have class 2 transformers & the replacements I ordered can't be. Changing out the wire is impractical. Individual transformers seem to be my best option.
 
Sparky,
check out the QTran units that I linked to in a previous post, they have a class 2 option that would get you in for a lot less transformers, I think each of theirs can have up to 15 breakers/feeds per unit, this would be a lot easier to wire than 22 primary feeds (you'd only need 2). I have had good luck with these units, and place them in attics quite often.

http://www.q-tran.com/pdf/QT_Catalog.pdf
 
mhulbert said:
Sparky,
check out the QTran units that I linked to in a previous post, they have a class 2 option that would get you in for a lot less transformers, I think each of theirs can have up to 15 breakers/feeds per unit, this would be a lot easier to wire than 22 primary feeds (you'd only need 2). I have had good luck with these units, and place them in attics quite often.

http://www.q-tran.com/pdf/QT_Catalog.pdf
Click to expand...

Thanks for the option. I still have to own up to the owners for ordering the wrong transformers.
 
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