Aluminum branch circuit wiring
Used widely in houses built between roughly the mid-1960s and mid-1970s. The cable itself is not the problem; the terminations are. Aluminum expands and contracts more than copper as it heats and cools, which works connections loose over decades, and it oxidises into a poor conductor where copper does not. The result is heat at outlets, switches and splices — which is why the previous page's warm-device symptoms and this one are so often the same house.