Wire Size Calculator
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Copper vs Aluminum Wire: Ampacity and When Each Is Used

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Copper and aluminum are the two conductor materials used in residential and commercial electrical wiring. Choosing between them affects cost, conductor sizing, and the type of hardware your connections require. This guide covers the key differences so you can make an informed decision — or ask better questions when working with a licensed electrician.

Why Material Matters for Wire Sizing

Conductor material affects sizing in two ways: resistivity and ampacity. Aluminum has higher electrical resistance per unit area than copper, which means two things:

  • An aluminum conductor must be larger (lower AWG number) to carry the same current as copper.
  • Aluminum produces more voltage drop per foot than copper at the same gauge.

The voltage-drop formula used in wire sizing calculations reflects this through the resistivity constant K — roughly 12.9 for copper and 21.2 for aluminum (in ohm·cmil/ft units, as published in NEC training references). Use the wire size calculator to see exactly how material choice shifts the recommended AWG for your specific run.

Ampacity Comparison by Common Size

The table below shows typical ampacity values from NEC 2023 Table 310.16 (75°C column, not more than 3 current-carrying conductors, 30°C ambient). These values apply to conductors in conduit or cable. Always verify against the current NEC edition adopted in your jurisdiction, and consult a licensed electrician before final design decisions.

AWG / kcmil Copper (75°C) Aluminum (75°C) Notes
6 AWG 65 A 50 A Smallest AL generally allowed per NEC 310.3(B)
4 AWG 85 A 65 A Common sub-panel feeder range
2 AWG 115 A 90 A Service entrance / large feeder
1/0 AWG 150 A 120 A Typical 100–125 A service range
3/0 AWG 200 A 155 A 200 A copper service; AL needs 4/0 for same load
4/0 AWG 230 A 180 A Common AL service entrance size

Source: NEC 2023 Table 310.16 (75°C column). Values shown are for reference only — consult the adopted NEC edition in your jurisdiction and a licensed electrician for design use.

Cost Differences

Aluminum wire is generally less expensive per foot than copper, and the price gap widens at larger gauges where the weight of copper becomes significant. For a 200 A service entrance or a long feeder run to a sub-panel, aluminum conductors can represent a meaningful material cost saving. However, the total installed cost also depends on conduit size (larger AL conductors need more conduit fill space) and whether AL-rated hardware must be purchased or replaced.

Termination Requirements for Aluminum

Aluminum oxidizes when exposed to air, forming a layer that increases connection resistance. Poor aluminum connections are a known fire hazard — particularly a concern with the undersized branch-circuit aluminum wiring installed in some homes in the 1960s–70s. Modern large-gauge aluminum conductors (6 AWG and above) are considered safe when installed correctly, with two important requirements:

  • Anti-oxidant compound: Apply a listed anti-oxidant (oxide-inhibiting) compound to aluminum conductors before making connections. The compound prevents the oxide layer from forming inside lugs and splice connectors. Check the connector listing — some AL-rated lugs come pre-filled; others require field application.
  • AL-rated (or AL/CU-rated) lugs and terminals: Terminals must be listed for aluminum use. Equipment marked "AL" or "AL/CU" is suitable. Standard copper-only lugs are not appropriate for aluminum conductors. In panels, check that the lug or breaker terminal is AL-rated before landing an aluminum conductor.

Where Each Material Is Commonly Used

Aluminum — typical applications

  • Utility service entrance conductors — the conductors from the utility transformer to your meter and main panel are almost always aluminum, including overhead service drops.
  • Sub-panel feeders — runs of 6 AWG and larger between panels in the same building, where cost savings are significant.
  • Large appliance branch circuits (dryers, ranges, HVAC disconnects) at 6 AWG or larger, where AL-rated receptacles or lugs are available.

Copper — typical applications

  • Standard branch circuits (15 A, 20 A) — 14 AWG and 12 AWG branch circuits are almost universally copper. The NEC generally discourages aluminum below 6 AWG (NEC 310.3(B)).
  • Low-voltage and signal wiring — communications, control, and data cables are copper.
  • Where space is limited — copper's smaller diameter for a given ampacity can matter in tight conduit fills or device boxes.
  • EV charger circuits — while AL is sometimes used at 6 AWG for a 50 A EV circuit, copper is more common given the compact size of the run and the cost difference at that gauge. See the EV charger wire size guide for more detail.

Using the Calculator with Aluminum vs Copper

When you select "aluminum" in the wire size calculator, it applies the higher resistivity constant (K ≈ 21.2) in the voltage-drop formula and looks up ampacity from the aluminum column of NEC Table 310.16. The result will generally be one or two AWG sizes larger than the equivalent copper result. This is expected and correct — you should size up, not try to use the same AWG you would for copper.

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