Wire Gauge Amperage Chart

Conductor sizing looks like a lookup and mostly is, right up until it is not. The published ampacity tables give three numbers for the same piece of wire, one for each terminal temperature rating, and the figure you are actually permitted to use is governed by the lowest-rated component anywhere in the circuit. In a normal house that is a 75 degree Celsius terminal on the breaker or the charger, which means the middle column is the honest one and the 90 degree column printed on the jacket is not the number you get to use.

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What ampacity does copper wire carry?

Copper first, because it is the default for a branch circuit inside a house. The last two columns are derived: the largest standard breaker the conductor supports using the governing figure, and the largest continuous EV charger output that breaker in turn supports at 80 percent.

The two rows that matter to almost every reader are 8 AWG and 6 AWG. Eight AWG copper is exactly 50 amps at 75 degrees, which covers a 50 amp breaker and a 40 amp charger with no margin whatsoever. Six AWG is 65 amps, which covers a 60 amp breaker and a 48 amp charger with genuine headroom. That headroom is the reason many electricians run 6 AWG for a 50 amp circuit even though 8 AWG is permitted: the material difference on a 40 foot run is small, and it leaves the circuit upgradeable to 60 amps later without opening the wall a second time.

What ampacity does aluminium wire carry?

Aluminium carries less current for the same physical size, so every row shifts. The rule of thumb is one size up, and the table below shows why: 4 AWG aluminium and 6 AWG copper both land on 65 amps in the governing column. On a short branch circuit that penalty is not worth taking. On a 150 foot feeder to a detached garage, where the conductor is most of the material cost, it very often is.

Aluminium is not a compromise material, but it is an unforgiving one at the terminations. It needs lugs and devices rated AL/CU or CO/ALR, an anti-oxidant compound such as Ideal Noalox or the ILSCO oxide inhibitor brushed onto the conductor, and torque applied to the manufacturer's specification rather than to feel. The full argument for and against sits in aluminium or copper wiring.

Why does the same wire have three ampacity numbers?

The three columns are insulation temperature ratings: 60, 75 and 90 degrees Celsius. They describe how hot the conductor's insulation can get before it degrades, and therefore how much current it can carry before it reaches that temperature. A 90 degree conductor is not a better wire in some vague sense, it is a wire whose insulation survives a higher temperature, which means it can carry more current before that temperature is reached.

The catch is that the wire is not alone in the circuit. It terminates on a breaker lug at one end and on equipment terminals at the other, and those components have their own temperature ratings. If a 90 degree conductor lands on a 75 degree lug, the lug is what gets hot, so the 75 degree column governs. Almost all residential breakers and almost all EVSE terminal blocks are rated 75 degrees, which is why the middle column is the practical one and why quoting the 90 degree number is a common way to make an undersized conductor look adequate.

The 90 degree column still earns its place. It is the correct starting point for derating calculations: you begin at the 90 degree ampacity, apply the ambient and conductor-count factors, and then the result is capped at the 75 degree column because of the terminals. On a heavily derated run that two-step process gives a better answer than starting at 75 and derating from there.

What makes the number in the table smaller?

Three adjustments, and any of them can cost you a wire size. The published table assumes not more than three current-carrying conductors in a raceway at an ambient of 30 degrees Celsius. Depart from either assumption and the figure comes down.

Ambient temperature

An attic run in a hot climate is the case that bites. A conductor that is fine in a basement can lose a fifth of its capacity crossing an attic in summer, and the calculation is not optional: the code sets the factors and the inspector applies them. This is a large part of why two identical-looking quotes for the same charger can specify different conductors, and why the cheaper one is not always the sloppier one. It may simply have picked a cooler route.

Conductor count in a raceway

Note that the equipment grounding conductor is not current-carrying under normal conditions and does not count, and a neutral that carries only unbalanced current in a three-wire circuit is treated separately. A single 240 volt EV circuit in its own conduit has two or three current-carrying conductors and takes no adjustment at all, which is the common case. Two EV circuits sharing one raceway, which happens in a two-EV household, immediately lands in the 80 percent band.

The small conductor rule

Regardless of what the temperature columns say, overcurrent protection is capped at 15 amps for 14 AWG copper, 20 amps for 12 AWG copper and 30 amps for 10 AWG copper, and at 15 and 25 amps for 12 and 10 AWG aluminium. That is why 10 AWG copper reads 40 amps in the 90 degree column and still cannot be protected above 30. For EV work this matters on the 30 amp circuit that feeds a 24 amp charger, which is the dryer-circuit case covered in dedicated circuit requirements.

When does distance decide the conductor instead of heat?

Frequently, and this is the point at which an ampacity chart stops being enough. Ampacity answers whether the conductor gets too hot. Voltage drop answers whether enough voltage arrives at the far end. They are different questions with different answers, and on a long run the second one governs.

Here is 48 amps in copper at increasing one-way distances. The commonly used design target is three percent on a branch circuit.

The three percent figure is a design recommendation in an informational note rather than a hard code requirement, which is precisely why it disappears from quotes and why it is worth checking yourself. Ignoring it does not fail an inspection, it simply means the charger sees reduced voltage for every hour of every session for the life of the installation, and the difference is dissipated as heat in the wall. The full grid at both 40 and 48 amps, in copper and aluminium, is on the voltage drop chart, and you can run your own distance in the voltage drop calculator.

What do you actually buy?

For a conduit run, individual THHN conductors: two hot legs in different colours, a neutral only if the equipment needs one, and a green equipment grounding conductor. A hardwired EVSE typically needs no neutral at all, which simplifies the pull. A 100 foot spool of 6 AWG THHN in black and a matching spool in red cover the two legs, with 8 AWG green for the ground.

For a cable run inside finished walls where conduit is not being installed, NM-B cable is the usual choice indoors and dry only. A 50 foot roll of 6/3 NM-B with ground or the longer 125 foot Southwire roll covers most residential runs. NM-B is not permitted in wet locations, outdoors, or buried, which is where the conversation moves to conduit and is covered in conduit for an EV charger circuit.

Note that NM-B cable carries an additional restriction: its ampacity is taken from the 60 degree column regardless of the 90 degree rating printed on the jacket. That single detail catches people out. It is why 6/3 NM-B is commonly used for a 50 amp circuit and why a 60 amp circuit in cable rather than conduit normally moves up to 4 AWG.

How to use this chart without misusing it

Use it to sanity-check a quote, to understand why one electrician specified a heavier conductor than another, and to work out whether upgrading the circuit later will mean replacing the wire. Do not use it to specify your own installation. Every real circuit involves a terminal rating you have not read, an ambient you have not measured, a raceway fill you have not counted and a distance that may override all three, and the person who reconciles those is a licensed electrician with the code book open.

If you want the reasoning rather than the table, the wire size guide walks through it in prose. If you want to see a complete parts list with the conductor already chosen and priced, the hardwired 48 amp buildout lists every line item with a total. And if you have not settled the amperage yet, start at the amperage and breaker chart, because the conductor is downstream of that decision rather than upstream of it.

Common questions

What wire size does a 50 amp EV charger circuit need?

A 50 amp breaker feeding a 40 amp charger is normally run in 6 AWG copper, which carries 65 amps in the 75 degree Celsius column that governs on typical residential terminals. Some short runs are done in 8 AWG copper, which is exactly 50 amps at 75 degrees and therefore has no margin at all for ambient temperature or voltage drop. Your electrician makes that call for your specific run.

What wire size does a 60 amp EV charger circuit need?

A 60 amp breaker feeding a 48 amp charger is normally run in 6 AWG copper on a short residential run, because 6 AWG carries 65 amps at 75 degrees Celsius. Longer runs move to 4 AWG copper, usually because of voltage drop rather than ampacity. In aluminium the equivalent is 4 AWG, which carries 65 amps at 75 degrees, one size larger than the copper.

Why does the same wire have three different ampacity numbers?

The three columns correspond to insulation and terminal temperature ratings of 60, 75 and 90 degrees Celsius. The number you are permitted to use is set by the lowest-rated component anywhere in the circuit, which in a house is almost always a 75 degree terminal on the breaker or the equipment. The 90 degree column is mostly used as a starting point for derating calculations rather than as an ampacity you can actually apply.

What is the small conductor rule?

Regardless of what the temperature columns say, overcurrent protection for 14, 12 and 10 AWG copper is capped at 15, 20 and 30 amps respectively, and 12 and 10 AWG aluminium at 15 and 25 amps. That is why 10 AWG copper shows 40 amps in the 90 degree column but can only ever be protected at 30. For EV work this matters mainly on a 30 amp circuit feeding a 24 amp charger.

Is aluminium wire safe for an EV charger circuit?

Modern AA-8000 series aluminium building wire is a code-recognised conductor and is entirely legitimate for a feeder. It needs lugs rated AL/CU, anti-oxidant compound at the terminations, correct torque and roughly one size increase over copper. The reputation the material carries comes from 1960s and 1970s branch-circuit wiring and the terminations used with it rather than from the metal itself. On a short branch circuit copper is still the default.

Does a longer run need a bigger wire than this chart shows?

Often, yes. This chart answers a heat question, and a long run is a voltage question. A 6 AWG copper conductor carrying 48 amps is thermally comfortable at 150 feet and electrically poor, because the drop has passed the three percent design target. That target is a recommendation rather than a hard requirement, so it is frequently ignored on quotes. Check your own distance before you buy wire.

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