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In our previous issue, we said that LV systems are covered by Article 411. The requirements actually begin with 411.3. The title of 411.3 seems to overlap with the title of Article 411. This subsection was added with the 2014 NEC, which also dropped 411.2 from the 2011 NEC. The 2014 revisions are confusing in several ways, and Article 411 is ripe for revision with the 2017 code cycle.
In the meantime, we have to work with what we've got. How do you know whether the NEC considers a lighting system “low voltage” or not? You’d look for the definition of “low voltage lighting” in the 2014 NEC. But as noted, the 2014 NEC dropped section 2 (which is normally where you find the definitions pertinent to a given Article). And the 2014 NEC did not bring it back.
The definition is contextual, and it’s repeated several times in Article 411. A low voltage lighting system is one that operates at 30V or less. But how is this different from a standard flashlight? Additional characteristics are that it has an isolating power supply, low-voltage luminaires, and associated equipment identified for the use [411.3].
In fact, the entire system must be listed (as a complete system) [411.1(A)]. This means you don’t buy a Class 2 power supply and a bunch of 30V lighting fixtures. That’s a very different model from, say, a 277V lighting system; you build your own and it’s not (normally) listed as a system.