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What Size Wire for 30, 50, 100 or 200 Amps?

For most circuits there is a single right answer, and for two of the common ones there are two right answers depending on a detail nobody mentions: what temperature your terminations are rated for. Here is each common amperage, what it takes in copper and aluminum, and where the answer changes.

Branch circuits and feeders

Minimum conductor size from NEC Table 310.16. The two copper columns are the same number until you reach 50 A, at which point the termination rating starts to matter.

Minimum copper and aluminum wire size by circuit amperage and termination temperature
CircuitCu 60°CCu 75°CAl 75°CTypical load
20 A120 V121412General receptacle and small-appliance circuits
30 A240 V101010Electric dryer, small subpanel, some water heaters
50 A240 V686Electric range, welder receptacle, EV charger
60 A240 V464Subpanel feeder, larger EV or spa loads

Sizes are for the ungrounded conductors. Equipment grounding conductors are sized separately from NEC Table 250.122 and are not covered here.

Why "what size wire for 50 amps" has two answers

Ask this question in any trade forum and you will get 8 AWG from half the room and 6 AWG from the other half, and both groups are right. Copper 8 AWG is rated exactly 50 A in the 75°C column, which covers a 50 A load precisely. In the 60°C column that same conductor carries only 40 A, which does not.

So if every termination on the circuit is listed for 75°C, 8 AWG is code compliant. If anything in the path is 60°C, you need 6 AWG. A lot of electricians simply run 6 AWG on 50 A circuits and stop thinking about it, which costs a little more copper and removes an entire category of mistake. That is a defensible habit rather than an overreaction.

The same split appears at 60 A: 6 AWG at 75°C versus 4 AWG at 60°C. Below 50 A it does not arise, because 240.4(D) already caps 14, 12 and 10 AWG at their 60°C values and the columns cannot disagree.

Services are sized by a different rule entirely

A 200 amp service does not need a conductor rated for 200 amps. NEC 310.12 permits the service conductors supplying the entire load of a one-family dwelling to be sized at 83% of the service rating, because diversified household load almost never approaches the panel rating continuously. That allowance is the difference between 3/0 AWG and 2/0 AWG copper, which is a real amount of money on a service run.

ServiceAt 83%CopperAluminum
100 A83.0 A4 (85 A)2 (90 A)
125 A103.8 A2 (115 A)1/0 (120 A)
150 A124.5 A1 (130 A)2/0 (135 A)
200 A166.0 A2/0 (175 A)4/0 (180 A)

These are derived rather than transcribed: 83% of the rating, looked up in the 75°C column of Table 310.16. They reproduce NEC Table 310.12 exactly, which is a useful check on both. The allowance runs from 100 A through 400 A, but above 200 A the aluminum sizes leave the AWG range and move into kcmil, so this table stops where the sourced data does.

Two conditions are easy to miss. The conductors must supply the entire dwelling load — a subpanel feeding part of the house does not qualify under this section. And it applies to one-family dwellings on 120/240 V single-phase, not to commercial services or apartment house mains.

Where distance overrules the table

Every number above answers one question: will the conductor overheat. On a long run a second question takes over. NEC 210.19(A) recommends keeping branch-circuit voltage drop under 3%, and the point at which a minimum-size conductor stops meeting that is closer than most people expect:

CircuitCopperMax one-way run at 3%
20 A @ 120 V14 AWG29 ft
30 A @ 240 V10 AWG99 ft
50 A @ 240 V8 AWG94 ft
60 A @ 240 V6 AWG122 ft

The 20 A / 120 V row is the one that surprises people. A 120 V circuit has half the voltage to lose, so it runs out of headroom in half the distance — a detached garage or a well pump at the back of a property routinely exceeds it. Note also that this recommendation is an Informational Note rather than an enforceable requirement in most jurisdictions, though some adopt it outright.

To check a specific run rather than read a threshold, the wire gauge calculator solves ampacity and voltage drop together and tells you which one is binding. The voltage drop formula shows the arithmetic if you would rather do it on paper.

Before you buy the wire

Two things commonly change the answer after it has been decided. If more than three current-carrying conductors share a raceway, the adjustment factors in NEC 310.15(C)(1) reduce ampacity and can push you up a size. If the run passes through a hot attic, the ambient correction factors in 310.15(B) do the same. Both are covered in the ampacity chart guide.

And once the conductor size is settled, the pipe has to hold it. Going up a gauge for voltage drop or for aluminum can push a run into the next trade size — check it against the conduit fill chart before you buy either. Sizing the conduit first and the conductor second is the usual way to end up doing both twice.

Sources

Grouped by manufacturer or publisher, then by document. Expand a group for the cited document, its verified-on date, and every value taken from it — all of it stays in the HTML either way.

NFPA(15 documents, 103 values)

Frequently asked questions

What size wire do I need for a 50 amp circuit?

8 AWG copper where terminations are rated 75°C, which covers most modern breakers and range receptacles. If any termination in the circuit is rated 60°C, you need 6 AWG instead, because 8 AWG copper carries only 40 A in the 60°C column.

What size wire for a 30 amp circuit?

10 AWG copper. This one is unambiguous: NEC 240.4(D) caps 10 AWG at 30 A of overcurrent protection, and 10 AWG copper is rated exactly 30 A in the 60°C column, so the wire and the breaker line up regardless of termination rating.

What size wire for a 100 amp service?

4 AWG copper or 2 AWG aluminum for a dwelling. NEC 310.12 permits service conductors carrying the entire load of a one-family dwelling to be sized at 83% of the rating — 83 A here — which is smaller than a straight 100 A lookup would give.

What size wire for a 200 amp service?

2/0 AWG copper or 4/0 AWG aluminum for a one-family dwelling, under the NEC 310.12 83% allowance. That works out to 166 A of required ampacity, met by 2/0 copper at 175 A or 4/0 aluminum at 180 A in the 75°C column.

Does the answer change for a long run?

Yes. Ampacity stops being the binding constraint once the run is long enough that voltage drop exceeds the 3% NEC 210.19(A) recommends. A 50 A circuit on 8 AWG copper reaches that point at about 94 feet one way; past that you go up a size.

Can I use aluminum wire for a branch circuit?

For services and feeders aluminum is common and economical. For small branch circuits it is rare — aluminum has no NEC-rated size below 12 AWG, needs listed terminations and antioxidant treatment, and the labor usually cancels the material saving on a short run. Most dwelling branch circuits are copper.