Concealed or exposed wiring?

Voltage drop has nothing to do with transformer capacity since the actual drop is in the wires themselves.

I thought voltage drop was a function of voltage and wiring gauge and length, especially if approaching the max load of the transformer, hence the different voltage taps available on some transformers -- then again, maybe that's just due solely on the length/gauge of the wire. In any case, I mention it just in case the 15 or so feet might make a difference.

All the wiring will be concealed.

Any ideas? Thanks!

I'm not sure I understand your situation exactly. You bought a kit from Eurofase, right? Is it one that plugs into an outlet or one that you would install like track lighting, or would the lights be recessed into the ceiling with the transformer hidden somewhere?

You definitely should not splice wire into the existing kit wiring and then hide the junction in the ceiling. Wire runs between the switch and the transformer, the transformer and the first light, and the first light and the second light should all be continuous. Any junctions as well as the transformer should be accessible.

@bill: Yes, this is a kit from Eurofase. It's one which has a class II transformer that is meant to be placed in a junction box. The lights will be recessed into two "niches", which are about 15 feet apart. Since it's low-voltage, could I not "splice" the load side wires? If I cannot, what are my alternatives?

I am reading from your first post that you are wanting to switch the low voltage. This is wrong. You should be switching the line (120 volt) side.
Not sure if is code requirement but I would only make splices at the transformer or the lights.

The basic layout should be

1) Your switch should be fed from the branch circuit.
2) The transformer should be in a junction box that is accessible - eg not behind a finished wall. The transformer will break eventually.
3) The power should run from the switch to the transformer on a continuous wire.
4) The wire between the transformer and the first light should be continuous.
5) The wire between the first light and the second light should be continuous.

Any wire that you use before the transformer should be of the same gauge as the wire coming to the switch. Any wire after the transformer needs to be of at least comparable gauge to the wires that came in your kit, just longer. If that means you have to buy some additional wire for any of those runs, so be it. Even if the chance starting a fire with a low voltage wire is small, it still isn't something you want to splice and then hide inside a wall or ceiling.

Treating 12V like normal voltage might seem like overkill, but you can easily start a fire with a 9V battery and some steel wool. Low voltage means that it won't kill you if you touch the wire. It doesn't mean that it can't create heat or a spark. If you are burying low voltage lights for landscaping, you don't really need to worry about catching the ground on fire. If you are going to put low voltage wires in your walls or ceiling or anything else that could burn, then you should take the same safety precautions that you would with any other wiring.