What Does The NEC Code Say?

CPSC (Consumer Product Safety Commission) research and subsequent studies prompted changes in the National Electric Code (NEC) regarding aluminum conductors. Despite concerns, the NEC addresses aluminum wiring in very few sections, mainly focusing on allowable alloys.

Before 1972, aluminum conductors were made with various alloys, often prone to mechanical issues like thermal expansion and bending failures. Alloys with additives were developed to mitigate these problems. The NEC now mandates the use of specific aluminum alloy conductors. Single-strand aluminum wiring is not available in branch circuit wiring for 15 or 20 amp residential branch wiring.

Furthermore, the NEC prohibits mixing conductors of dissimilar metals in terminals or connectors unless the device is designated for such use. Manufacturers label products accordingly, typically requiring UL listing for approval by electrical inspectors. However, twist-on aluminum wire connectors have shown susceptibility to failures in independent tests, raising concerns about the adequacy of UL testing standards.