Nec 725.51?

[chuck@apsinc.biz]

I am working on a project that has an architectural cove. In the base of this cove I want to put a mini-down light, this down-light is Low-Voltage 35W MR11. I purchased a Class 2, 60VA fused electronic transformer.

The transformer looks like a car key fob and has 4-wires coming off of it. (1)Black, and (1)White for the 120V AC Supply side Feed and (2) red for the 12VAC Load Side Feed. There are no provisions to be connected to a junction box ect., it literilly is a small black box with 4 wires coming out of it.

NEC 725.51 Says conductors and equipment on the supply side of the power source shall be installed in accordance with the appropriate requirements of Chapters 1 through 4.......

I have a 120V, 20A MC Whip coming to the fixture location. I am struggling with how do I interface the MC whip and the line side power of the transformer.

Do I set a J-box, put the transformer in the J-box, and run the 12V wires through a grommet out of the J-Box then continue with the LV wiring to the Mini-Can?

Do I set a J-box, leave the transformer out of the J-Box and run the 120v leads through a grommet into J-Box and make the 120V connection.

Do I terminate the MC cable into a connector and make the 120V connection to the transformer in the open?

Any input would be greatly appreciated.

 

[rcarroll]

So, there is a place to mount a J-box. That's good. All line volt splices need to be in a box. I would install the x-former in a big enough box for all splices. Run the LV wires thru a bushing. Is there a problem with heat dissipation?

 

[Dennis Alwon]

Do I set a J-box, put the transformer in the J-box, and run the 12V wires through a grommet out of the J-Box then continue with the LV wiring to the Mini-Can?

Do I set a J-box, leave the transformer out of the J-Box and run the 120v leads through a grommet into J-Box and make the 120V connection.

Do I terminate the MC cable into a connector and make the 120V connection to the transformer in the open?

Any input would be greatly appreciated.

You have to purchase a junction box for the transformer. The manufacturers of the transformer usually make an enclosure for it, however, many lighting places don't know about it and don't stock it.
The 110 volt wiring needs to be in the JB. The low voltage wire can exist the box thru a grommet of sorts but must be of high voltage insulation. You cannot use bell wire or phone wire (I have seen this often) in the same enclosure as the high voltage wire. You can use a piece of mc to exist the box if you like. Also any wiring for this light must be exposed unless it is accepted by the NEC to be concealed. Again you cannot fish 2 pieces of #12 THHN down a wall just because it is low voltage.

I can be a little wordy and confusing so read Article 411

 

[Jljohnson]

Most of the transformers like you describe that I have seen are mounted inside of a 1-gang box and all splices are made in that box(Line volt and Low volt). The only catch is the LV wiring must be rated for the highest voltage present in the box. We do this in a Resi application by using NM cable for the LV wiring.

 

[infinity]

Most of the transformers like you describe that I have seen are mounted inside of a 1-gang box and all splices are made in that box(Line volt and Low volt). The only catch is the LV wiring must be rated for the highest voltage present in the box. We do this in a Resi application by using NM cable for the LV wiring.

I don't see how the class 2 low voltage wire can be in the same junction box as the 120 volt power conductors unless it comes from the manufacturer that way.

 

[Jljohnson]

The transformers I am thinking of are designed to fit the 6/32" holes in a one gang box and be mounted directly behind a 1-gang blank cover. I have seen them in 60 watt(1-gang), 120 watt(2-gang), and 180 watt(3-gang). I'm pretty sure the manufacturer's instructions tell you install the way I have described.

 

[Dennis Alwon]

I don't see how the class 2 low voltage wire can be in the same junction box as the 120 volt power conductors unless it comes from the manufacturer that way.

I am not sure if Article 411.4 (A)(2) clears it up or not.

 

[JohnJ0906]

Most of the transformers like you describe that I have seen are mounted inside of a 1-gang box and all splices are made in that box(Line volt and Low volt). The only catch is the LV wiring must be rated for the highest voltage present in the box. We do this in a Resi application by using NM cable for the LV wiring.

I've seen these too. We usually use a 4" square w/ extention ring. There really is no other way to have the 120v in a box unless the 12v is also in there too. All 4 wires come out of the transformer on the same side.

 

[don_resqcapt19]

Trevor,

I don't see how the class 2 low voltage wire can be in the same junction box as the 120 volt power conductors unless it comes from the manufacturer that way.

What about 725.55(D)?
Don

 

[infinity]

Trevor,

What about 725.55(D)?
Don

So you're saying is that if the Class 2 circuit is installed with a Class 1 wiring method then it would be OK. I was hung up on the .25" of separation.

 

[don_resqcapt19]

Trevor,

So you're saying is that if the Class 2 circuit is installed with a Class 1 wiring method then it would be OK. I was hung up on the .25" of separation.

I am saying that where there is a device that has both Class 1 and Class 2 wiring, then it can be a single enclosure as long as the wires are seperated by 1/4".
Don