ReferenceNEC 2023 Tables 310.16 and 250.122 · Updated

Sub panel wire size chart

A 100 amp sub panel needs 3 AWG copper or 1 AWG aluminum feeder wire, with an 8 AWG copper ground, per NEC Table 310.16 at 75°C. A 60 amp sub panel needs 6 AWG copper or 4 AWG aluminum. On a 240V feeder those 100A sizes hold voltage drop under 3% up to 146 ft in copper and 142 ft in aluminum; longer runs need larger wire.
60A6 Cu / 4 Al
100A3 Cu / 1 Al
125A1 Cu / 2/0 Al
200A3/0 Cu / 250 Al

Sub panel wire size by breaker

Smallest feeder conductors NEC Table 310.16 allows at 75°C, the copper equipment ground from Table 250.122, and the longest one-way run that keeps that size under 3% voltage drop at 240V with the full breaker rating as load.
Feeder breakerWire sizeGround (Cu)Max run, ft
CopperAlum.CopperAlum.
30A108109693
35A881013180
40A881011570
45A861010298
50A86109288
60A6410121117
70A438166127
80A428145140
90A328162125
100A318146142
110A21/06168162
125A12/06186180
150A1/03/06196190
175A2/04/06212205
200A3/0250k6234212

Sizes are AWG; “k” means kcmil (250k = 250 kcmil). Assumes individual THWN-2 or XHHW-2 conductors in conduit, breaker and panel lugs marked 75°C, 30°C (86°F) ambient and no more than three current-carrying conductors. NEC 240.4(D) is applied to 10 AWG. NM-B cable and 60°C terminals need a larger size: see the wire size page for your breaker. Source: NEC 2023 Tables 310.16 and 250.122, Chapter 9 Table 8; ampacity values checked November 14, 2026.

Wire size by distance

Find the breaker that feeds the sub panel, then read across to the one-way length of the run. These tables size the wire for the code minimum and for a voltage drop under 3% with the full breaker rating flowing at 240V. The NEC recommends 3% on a feeder in an informational note (215.2(A)); it is a design target, not a mandatory limit. If your calculated load is well below the breaker rating, the voltage drop calculator will often show a smaller size is enough.

Copper feeder

Copper feeder size by one-way run length, 240V single-phase, load equal to the breaker rating, voltage drop under 3%. AWG unless marked kcmil. Shaded cells are larger than the code minimum; the small figure is the copper ground that goes with them.
AmpsOne-way run, feet
255075100150200300
30A1010108gnd 88gnd 86gnd 64gnd 4
35A88886gnd 86gnd 84gnd 4
40A88886gnd 84gnd 43gnd 4
45A88886gnd 84gnd 43gnd 4
50A8886gnd 84gnd 44gnd 42gnd 4
60A66664gnd 63gnd 62gnd 4
70A444443gnd 61gnd 4
80A44443gnd 62gnd 41/0gnd 3
90A333332gnd 61/0gnd 4
100A33332gnd 61gnd 42/0gnd 3
110A222221gnd 42/0gnd 2
125A111111/0gnd 43/0gnd 3
150A1/01/01/01/01/02/0gnd 43/0gnd 4
175A2/02/02/02/02/02/04/0gnd 4
200A3/03/03/03/03/03/0250kgnd 4

Aluminum feeder

Aluminum feeder size by one-way run length, 240V single-phase, load equal to the breaker rating, voltage drop under 3%. AWG unless marked kcmil. Shaded cells are larger than the code minimum; the small figure is the copper ground that goes with them.
AmpsOne-way run, feet
255075100150200300
30A8886gnd 84gnd 44gnd 42gnd 4
35A8886gnd 84gnd 44gnd 42gnd 4
40A886gnd 86gnd 84gnd 43gnd 41gnd 3
45A6664gnd 64gnd 62gnd 41gnd 4
50A6664gnd 63gnd 62gnd 41/0gnd 3
60A44442gnd 81gnd 62/0gnd 4
70A33332gnd 61gnd 42/0gnd 3
80A22221gnd 61/0gnd 43/0gnd 3
90A22221gnd 62/0gnd 43/0gnd 3
100A11111/0gnd 62/0gnd 44/0gnd 3
110A1/01/01/01/01/02/0gnd 44/0gnd 3
125A2/02/02/02/02/03/0gnd 4250kgnd 3
150A3/03/03/03/03/04/0gnd 4300kgnd 3
175A4/04/04/04/04/04/0350kgnd 3
200A250k250k250k250k250k250k400kgnd 3

Example: a 100A sub panel in a detached garage 200 ft from the main panel. The code minimum is 1 AWG aluminum, which stays under 3% only to 142 ft. At 200 ft the table gives 2/0 AWG aluminum (2.65% drop), and the copper ground grows from 8 AWG to 4 AWG to match.

Why the ground wire grows with the feeder

NEC 250.122(B) says that when the feeder conductors are made larger than the minimum, for voltage drop for example, the equipment grounding conductor has to be increased by the same proportion of circular-mil area. The small “gnd” figure in each shaded cell is that larger copper ground. Unshaded cells use the Table 250.122 size in the first table.

What the feeder needs besides the right size

A feeder to a 120/240V sub panel has four conductors: two hots, a neutral and an equipment ground. The neutral bar in the sub panel is kept separate from the ground bar and the enclosure. A sub panel in a detached building also needs its own grounding electrode (NEC 250.32(A)). The steps are in the sub panel installation guide and the detached garage wiring guide.

The smaller sizes NEC 310.12 allows for a dwelling service (2/0 copper or 4/0 aluminum at 200A) apply only to a service or a feeder that carries the whole load of the dwelling. A sub panel that carries part of the load is sized from Table 310.16, as on this page.

For a buried run, check the burial depth chart for the cover your conduit or cable needs, and the standard breaker sizes if your load falls between two ratings.

Frequently asked questions

What size wire do I need for a 100 amp sub panel?

3 AWG copper or 1 AWG aluminum, with a 8 AWG copper equipment ground, for conductors in conduit on 75°C terminals (NEC Table 310.16 and Table 250.122). At 240V and a full 100A load those sizes stay under 3% voltage drop up to 146 ft in copper and 142 ft in aluminum.

What size wire for a 60 amp sub panel?

6 AWG copper or 4 AWG aluminum, with a 10 AWG copper equipment ground, for conductors in conduit on 75°C terminals (NEC Table 310.16 and Table 250.122). At 240V and a full 60A load those sizes stay under 3% voltage drop up to 121 ft in copper and 117 ft in aluminum.

What size wire for a 125 amp sub panel?

1 AWG copper or 2/0 AWG aluminum, with a 6 AWG copper equipment ground, for conductors in conduit on 75°C terminals (NEC Table 310.16 and Table 250.122). At 240V and a full 125A load those sizes stay under 3% voltage drop up to 186 ft in copper and 180 ft in aluminum.

What size aluminum wire for a 150 amp sub panel?

3/0 AWG aluminum, with a 6 AWG copper equipment ground, on 75°C terminals (NEC Table 310.16). That size holds a full 150A load under 3% voltage drop up to 190 ft at 240V. The lugs must be marked for aluminum conductors.

How far can I run a sub panel feeder before I need bigger wire?

It depends on the load and the wire. With the full breaker rating as the load at 240V, the code-minimum copper feeder stays under 3% voltage drop to 121 ft at 60A, 146 ft at 100A and 234 ft at 200A. A 60A copper feeder at 150 ft needs 4 AWG instead of 6 AWG.

Does the ground wire have to be bigger when I upsize for voltage drop?

Yes. NEC 250.122(B) requires the equipment grounding conductor to be increased in proportion to the feeder conductors. For a 100A aluminum feeder upsized from 1 AWG to 2/0 AWG, the copper ground goes from 8 AWG to 4 AWG.

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Important: For reference only. Not a substitute for a licensed electrician. Electrical work can cause serious injury, death, fire, or property damage if performed incorrectly. Always hire a licensed electrician for electrical work, especially for service upgrades, panel work, and 240V circuits. Values are derived from NFPA 70 (NEC) for educational purposes. Always verify against your locally adopted NEC edition and amendments - local jurisdictions may enforce stricter requirements. WireRef provides reference information only and is not responsible for work performed based on this content. NEC® is a registered trademark of the National Fire Protection Association. Free NEC access via NFPA · OSHA Electrical Safety · Terms of use.

NEC 2023 references verified February 2026