I've been wondering why the NEC code insists on using metal raceways once electrical circuits enter a living space. What's the reasoning behind this requirement? Additionally, does anyone know if the CEC has similar guidelines? I also have some 3/4" liquid tight flexible metal conduit lying around—can I use this inside my building?
2 Answers
In the U.S., if you're running DC circuits inside a building, you definitely need to put them in conduit. This requirement helps prevent potential fire hazards caused by rodent damage; if a DC arc starts, it can keep going and cause bigger issues. The code is particularly strict about using solid metal raceways for this reason.
The NEC's requirement for using metal raceways mainly comes from older safety standards aimed at protecting live circuits within buildings. Originally, they only mandated metal raceways once circuits entered the building, but over the years they have added more safety measures. Since 2011, metal conduit has been required both inside and on buildings, especially for solar PV source circuits. Reflective labeling and other more stringent regulations have also been put in place to ensure safety. By the way, yes, liquid tight flexible metal conduit (LFMC) can be used, which is specified in section 690.31 of the NEC.