Aluminum vs copper wire for an EV charger

This question usually arrives with a quote attached. The electrician has priced aluminum for a long run to a detached garage, or copper for a short run to the garage wall, and the homeowner wants to know whether they are being sold something inferior. They are not. Both are ordinary, listed materials -- they simply behave differently.

The ampacity difference, in numbers

Read the 60-amp row of your own project off that table and the pattern is clear. A 60 A EV circuit is comfortably inside #6 copper at 65 A. The same circuit in aluminum steps up to #4 at 65 A, because #6 aluminum is only good for 50 A.

Where each one wins

Terminations are the real issue

Aluminum's reputation comes from old branch-circuit wiring and from connections made with devices that were never rated for it. Modern aluminum building wire is a different alloy, and the rules around it are about the ends rather than the middle: every lug, breaker and terminal has to be listed for the conductor material, joints need the right connectors and compound, and terminations must be made up to the specified torque.

What does not change

• The breaker size. A 48 A charger is a 60 A circuit in either material.
• The charger. It cannot tell what it is fed with.
• Charging speed. A correctly sized conductor of either material delivers the same current.
• The permit and inspection. Both are ordinary, listed materials; neither is a shortcut past the process.

Voltage drop applies to both

On a long run, the size that satisfies ampacity may still not be the size you want, because voltage drop grows with distance and aluminum's higher resistance makes it grow faster. The published 240 V tables put a 50 A copper circuit at #6 out to 150 ft, and the same circuit in aluminum at #4. Voltage drop on long runs has the table.

That interaction is exactly why this is a decision for the person doing the job. Bring the question; do not bring the answer.

Conditions the published table assumes

An ampacity figure is not a fixed property of a wire. The chart above is stated for specific conditions -- an 86 F ambient, no more than three current-carrying conductors, and the insulation temperature column the installer is allowed to use. Hot attics, sun-exposed conduit, bundled conductors and long runs all push the real answer toward a larger size, in either material.

That is worth knowing for one reason: if two quotes name different conductor sizes for the same circuit, neither electrician is necessarily wrong. They may be reading different conditions along your particular route.

Two practical side effects

• Conduit size. Aluminum is physically larger for the same ampacity, so an existing conduit that fits copper may not fit the aluminum equivalent. On a rewire through existing conduit, that alone can decide it.
• Handling. Larger conductors are stiffer to pull and to dress into a panel, which shows up as labor rather than material on the quote.

What to ask for on the quote

1. 1.The conductor size and material for the branch circuit, in writing.
2. 2.Confirmation that every termination is rated for that material -- breaker, lugs, receptacle or charger terminals.
3. 3.Whether the size accounts for the run length, not just the breaker. Voltage drop.
4. 4.Whether the price difference is material or labor. If aluminum saves $80, the copper is worth taking.