Low voltage transformers question

11 years ago

I am planning to use several (many) led fixtures, some of which will be on monorail-style track lighting. I may have as many as eight separately switched circuits. The lighting store tells me that each circuit needs to have a separate transformer, and that circuit is switched at the 110 volt level, before the transformer. What is wrong with just having a single, larger transformer and switch the low voltage lines? The problem with separate transformers is where to put them. I would run the wires from the breaker box to the switch, then up to the roof rafters (this is a one-story, cathedral ceiling building), route out a groove in the top of the rafter, go over to a point above the light location, then down through a hole bored through the rafter to the light. Where in this run could I locate the transformer? Inside the wall, just above the switches?

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Comments (5)

Ron Natalie
11 years ago
Most of the LED transformer outputs are DC. Most switches for household lighting use are not rated for DC.
The fancier switches (dimming, remote control, scening,e tc..) won't work at all unless fed with 120VAC.

Typically the transformer is just placed somewhere along the monorail where it's convenient to run the 120V feed.
Ron Natalie
11 years ago
Most of the LED transformer outputs are DC. Most switches for household lighting use are not rated for DC.
The fancier switches (dimming, remote control, scening,e tc..) won't work at all unless fed with 120VAC.

Typically the transformer is just placed somewhere along the monorail where it's convenient to run the 120V feed.
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geoffrey_b
11 years ago
I'm not an electrician - but I am an engineer. I have installed low voltage lighting in a kitchen and two bathrooms.

One thing you should know is that there is more of a voltage drop with 24v - you can find voltage drop / cable size calculators on the internet.

The transformer should be somewhere like a closet. The heat in the attic may shorten it's life.

My lights are controlled by a magnetic dimmer. You need a transformer for each group of lights.

WAC makes some nice low voltage lights.
mtvhike
Original Author
11 years ago
In consultation with my supplier, I come up with the attached diagram showing my thoughts about wiring the kitchen lighting (part). The green wires are coming from the basement through a wall between the kitchen and a closet. There will be dimmer switches in that wall (two shown). The 110 volt wires then continue up through the wall to a shelf in the closet where the transformers will be located. I was going to put them inside the wall, but my supplier said that that's not allowed. The low voltage wires then continue up through the wall and through the ridge beam and then run along the top of the rafter to a hole drilled through the rafter and down to the monorail track. Question: do I have to put a box on the underside of the rafter, or can there be a tube attached to the rafter through which the wires run? Anyway, the monorail will have two circuits, one with down task lighting and the other with lights shining up to the ceiling. These would be independently controlled. Another, similar, monorail would be over the kitchen counter with a similar pair of lighting circuits. The dimmers and transformers for these circuits are not shown, but would be next to the ones which are shown.
Ron Natalie
11 years ago
You can put them wherever you like as long as it's accessible. Be careful with ventillation requirements. I've had some installed in boxes that just kept termal cycling off because there wasn't enough cooling.

As long as you're not making wiring connections, you don't need boxes at the transitions. You can run your cable up the wall and through bored holes in the rafter without a box. If there's some sort of decorative tube coming down from the rafter to the monorail, that's fine, if it's metal, you'll need some sort of bushing on the end to make sure it doesn't chafe the wires.