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When was aluminum wiring allowed for 15 and 20 amp circuits in new homes and mobile homes
Executive summary
Solid aluminum branch‑circuit wiring for 15‑ and 20‑amp circuits was widely used in U.S. homes and mobile homes from about the mid‑1960s into the early 1970s; it “met most local codes until the practice was ended” around 1974 and HUD stopped allowing it in manufactured homes after HUD jurisdiction began in 1976 [1] [2]. Modern NEC/industry guidance sizes aluminum differently than copper — historically #12 Al for 15 A and #10 Al for 20 A — but concerns about the older AA‑1350 alloy installations led to suspensions and strong safety warnings from the CPSC and building authorities [3] [4] [5].
1. What the historical record says: the 1960s–1970s aluminum boom
Aluminum branch‑circuit wiring was adopted widely during copper shortages in the mid‑1960s through the early 1970s, and many homes and mobile homes built in that era used solid aluminum for 15‑ and 20‑amp circuits [6] [7]. The U.S. Consumer Product Safety Commission estimated roughly two million homes and mobile homes constructed since 1965 used aluminum wiring and issued safety recommendations in 1974 after finding elevated risk factors in older aluminum installations [5] [1].
2. Code status then vs now: allowed, then restricted in practice
Solid aluminum for small branch circuits was permitted and used historically (the practice “met most local codes until the practice was ended in 1974”), but mounting evidence of connection failures prompted regulatory action, industry suspensions and advisories — particularly around the older AA‑1350 alloy — leading to the practical end of routine use in 15/20 A branch circuits by the mid‑1970s [1] [3]. For manufactured/mobile homes HUD jurisdiction beginning in 1976 resulted in a practical ban on aluminum branch wiring in those units [2].
3. The size‑equivalence rule reviewers quote
Where aluminum is used, industry and inspection guidance show that a larger aluminum conductor is required to achieve the same ampacity as copper: historically #12 aluminium was used for 15 A circuits and #10 aluminium for 20 A circuits; contemporary texts and inspection guidance repeat that equivalence [4] [8] [9]. Several practical guides and NEC‑based summaries advise that to put a 20‑amp circuit on aluminum you must step up to #10 Al [10] [11].
4. Why it became controversial: connection failures and alloy chemistry
Investigations in the late 1960s–early 1970s found that older “old‑technology” aluminum alloys (AA‑1350) and device terminations not rated for aluminum led to higher rates of loose, overheating connections and, in some cases, fires; that spurred re‑evaluation and the development of “new‑technology” AA‑8000 series alloys and CO/ALR‑rated devices [3] [12]. The CPSC and industry literature emphasize that poor terminations, thermal expansion and oxidation were key failure modes [5] [7].
5. Mobile homes: earlier cutoff and formal HUD action
Mobile/manufactured homes stopped using aluminum branch‑circuit wiring earlier than site‑built houses in practice; sources state aluminum branch wiring “has not been used in mobile homes since the early 1970s” and HUD’s regulatory oversight, starting in 1976, codified that shift [2] [6]. Older mobile homes (pre‑1976) can still contain aluminum branch wiring and therefore are commonly flagged by inspectors [13].
6. Contemporary code and practice: limited, alloy‑specific use
Current guidance and NEC‑based summaries require matching ampacity via larger wire sizes and, in practice, copper is used nearly exclusively for 15/20 A general‑purpose branch circuits in modern construction; where aluminum is used today it is typically a different alloy (AA‑8000 series), stranded for larger circuits, or copper‑clad aluminum — and devices/terminations must be rated for Al/Cu use [3] [4] [14]. Some technical forums note that small solid Al conductors became scarce on the market and that practical availability also restricted use [15].
7. Practical takeaway for homeowners and buyers
If you own or are buying a house or mobile home from the 1965–1975 window, expect the possibility of solid aluminum in 15/20 A branch circuits and treat it as an inspection item — inspectors advise verifying conductor size, device compatibility (CO/ALR or CU‑AL markings), and condition because older installations were associated with elevated hazard indicators (warm plates, odors, flicker) [7] [4] [5]. Available sources do not mention a single definitive nationwide “ban” date for site‑built homes, but multiple sources indicate the practice effectively ended in the mid‑1970s and HUD rules removed it from manufactured home practice by 1976 [1] [2].
Limitations: available sources do not provide a single NEC clause citation giving the exact year the NEC banned solid aluminum for 15/20 A branch circuits in site‑built homes; reporting instead shows a patchwork of industry suspension, CPSC action [16] and HUD regulation [17] that together ended routine use [5] [1] [2].