Low-voltage recessed wiring questions

jmasekFebruary 28, 2010

Hi all -

We want to wire five Nora MR-11 low-voltage recessed light fixtures (2") to a 300W torroidal magnetic transformer, as part of a kitchen rehab.

This first venture into low-voltage wiring has us baffled...

First, how do we connect the transformer output wire (12V) to the fixtures? According to instruction diagrams, each fixture has an 18" braided wire and plug that connects to a multi-tap connector, which receives the 12V output wire from the transformer. Since the other fixtures are farther apart than 18", we can not plug them into this multi-tap connector and we will need some sort of "extension wiring".

Second, rather than use a multi-tap connector, should we cut off the braided wire plug and connect the wires to the transformer output with wirenuts inside an electrical box? This would seem to conform to code, but the instructions say nothing about this option.

Third, what guage wire should we use? The distance from the transformer to the farthest fixture is about 16 feet. The instructions for the lights and transformer are not too clear. The transformer installation sheet has a voltage drop table that suggests runs of up to 90 feet are possible with thicker-gauge wire. But the MR-11 installation sheet says "Transformer must be mounted within 18 inches of an individual fixture".

Any help with this would be appreciated!

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You've entered into the often misunderstood world of low voltage power wiring. Basically you have to treat the wiring just like 120V wiring with junction boxes UNLESS you use class 2 power limited transformers. This is what is required with typical low voltage puck light installation. Wiring must still be in wall rated to pass though the structure. Not all combinations of low voltage lighting installation parts by manufacturers are UL listed (and some will tell you that)so it is possible that you can't even connect what you have been given in a code approved way. For these parts to be compatible the transformer will have five 5 amp fuses or circuit breakers on it, each meant to supply up to 60 watts of lighting. So each fixture will have it's own run of cable back to its own connection point on the transformer.

It's OK to lengthen runs using the manufacturer's voltage drop table and recommended wire size.

    Bookmark   March 2, 2010 at 11:02AM
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Usually, a wire gauge of 18 is sufficient for 12V fixture. It's true that you'd want a heavier gauge wire if your lights are over maybe 30 or 40 feet from the power source, but 18 gauge should be fine.

Those directions sound confusing and conflicting! I don't see any reason for the light to have to be within 18" of the transformer.

    Bookmark   March 10, 2010 at 8:19PM
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