Wire Size and Ampacity Guide: AWG Charts for 15A to 100A Circuits

Wire Gauge and Ampacity: The Core Relationship

Electrical wire sizing follows a straightforward principle: the thicker the wire, the more current it can safely carry. In the American Wire Gauge (AWG) system, the numbers work in reverse—lower AWG numbers mean thicker wire and higher ampacity. Selecting the wrong wire size for a given load is one of the most common causes of overheating, tripped breakers, and electrical fires.

Ampacity—the maximum continuous current a conductor can carry without exceeding its temperature rating—depends on wire material (copper vs. aluminum), insulation type, installation method, and ambient temperature. The values published in the National Electrical Code (NEC) Table 310.16 serve as the standard reference for residential and commercial wiring in the United States.

What Size Wire for a 15 Amp Circuit?

14 AWG copper wire is the minimum required for a 15-amp circuit under NEC guidelines. It is rated at 15 amps at 60°C and is the standard choice for general-purpose lighting and outlet circuits in residential construction. Some electricians prefer to run 12 AWG (rated 20 A) on 15-amp circuits to provide a safety margin and reduce voltage drop over longer runs.

The 80% continuous load rule applies here as well: if a circuit will carry a sustained load (three hours or more), the wire and breaker must be sized so the continuous load does not exceed 80% of the breaker rating. On a 15-amp breaker, that means no more than 12 amps of continuous load.

Common 15-Amp Circuit Applications

• General bedroom and living room outlets
• Lighting circuits (LED, fluorescent, and incandescent)
• Smoke detector and low-draw bathroom circuits
• Garage door opener dedicated circuits

10 Gauge Wire Amps and 8 AWG Wire Ampacity

10 AWG copper wire carries 30 amps at 60°C and 35 amps at 75°C, making it the standard wire for 30-amp circuits such as electric dryers and water heaters. It is also commonly used for 240V circuits powering window air conditioning units and smaller HVAC equipment.

8 AWG copper wire has an ampacity of 40 amps at 60°C and 50 amps at 75°C. It is specified for 40- to 50-amp circuits, including electric ranges, large air conditioners, and EV Level 2 charging stations. The 8 AWG conductor is notably stiffer than 10 AWG and requires appropriate connectors and conduit fill calculations in multi-wire runs.

A practical note: when running 8 AWG or 10 AWG in conduit with other current-carrying conductors, NEC derating factors (Section 310.15(B)(3)) reduce the rated ampacity. For example, four to six current-carrying conductors in the same conduit require the tabulated ampacity to be multiplied by 0.80.

6 AWG Max Amps and Breaker Sizing

6 AWG copper wire is rated for 55 amps at 60°C and 65 amps at 75°C. The most common breaker paired with 6 AWG is a 60-amp double-pole breaker, which accounts for conductor temperature ratings at the breaker terminals—most residential breakers are rated at 60°C or 75°C, and terminal ratings govern the sizing decision under NEC 110.14(C).

What size breaker for 6 gauge wire depends on the application:

• Hot tubs and spas: 50- or 60-amp GFCI breaker with 6 AWG
• EV charging (Level 2): 50-amp breaker with 6 AWG at 40-amp continuous load
• Electric stoves/ranges: 50-amp breaker, though 8 AWG is sometimes permitted at 40 A
• Sub-panel feeder: 60-amp breaker as the main disconnect

Never oversize the breaker beyond the wire's ampacity. A 100-amp breaker on 6 AWG wire creates a dangerous condition: the breaker will not trip before the wire overheats.

Wire Size for a 100 Amp Sub Panel

For a 100-amp sub-panel fed with copper conductors, the NEC-minimum wire size is #4 AWG copper using 75°C-rated conductors (85 A), though most electricians specify #2 AWG copper (rated 95–115 A) to comfortably meet the 100-amp rating and accommodate voltage drop over the run. The choice depends on the distance from the main panel:

• Short runs (under 50 ft): #2 AWG copper or #1/0 AWG aluminum
• Medium runs (50–100 ft): #1 AWG copper or #2/0 AWG aluminum
• Long runs (100–150 ft): #1/0 AWG copper or #3/0 AWG aluminum to keep voltage drop under 3%

Aluminum conductors are a cost-effective alternative and are commonly used for sub-panel feeders. What size copper for a 100-amp service is typically 2 AWG for the hot conductors, with a 4 AWG copper ground and a 4 AWG copper neutral (or matched to local AHJ requirements).

A dedicated ground bar must be installed in the sub-panel, and the neutral and ground bars must be kept separate (unbonded) in any sub-panel that is not the service entrance.

4/0 Welding Cable Amp Rating and Industrial Applications

Welding cable operates under different standards than NEC building wire. 4/0 AWG welding cable is rated at approximately 400–600 amps depending on the duty cycle, cable length, and whether it is used for welding or general power transmission. The Electrical Apparatus Service Association (EASA) and cable manufacturers typically publish ampacity tables for welding cable based on duty cycle percentages (e.g., 60%, 40%, 20%).

Welding cable is constructed with fine-stranded annealed copper conductors and highly flexible rubber or EPDM insulation, which gives it far greater flexibility than NEC-rated THHN or XHHW wire of the same gauge. This makes 4/0 welding cable a popular choice for:

• MIG, TIG, and stick welding equipment leads
• Battery interconnects in industrial vehicles and forklifts
• Generator and inverter output leads
• Temporary power distribution on construction sites

4/0 welding cable should not be substituted for NEC-rated building wire in fixed installations. It does not carry a UL listing for permanent wiring and is not suitable for conduit installation under the NEC. For permanent 200-amp circuits, specify 4/0 AWG THHN or USE-2 rated copper conductors instead.

Voltage Drop and Wire Sizing Beyond Ampacity

Ampacity tables address thermal safety, but voltage drop is a separate sizing constraint that matters especially on long runs. The NEC recommends keeping voltage drop to 3% or less on branch circuits and 5% or less on the combined feeder-plus-branch circuit run. Voltage drop increases with current and distance, and decreases with larger wire cross-section.

The basic voltage drop formula for single-phase circuits is:

VD = (2 × K × I × L) ÷ CM

Where K = 12.9 for copper (resistivity constant), I = load current in amps, L = one-way wire length in feet, and CM = circular mils of the conductor (available in NEC Chapter 9, Table 8). For a 30-amp circuit running 100 feet on 10 AWG copper, the voltage drop calculates to approximately 3.8 volts on a 120V circuit—just over 3%—which is the threshold where upsizing to 8 AWG becomes advisable.

Frequently Asked Questions

• Can I use 12 AWG wire on a 15-amp circuit?

  Yes. 12 AWG is rated higher than needed for a 15-amp circuit and is perfectly acceptable. Some electricians prefer it for longer runs to reduce voltage drop, and it also allows the circuit to be upgraded to 20 amps later simply by swapping the breaker.

• Is 6 AWG wire OK for a 100-amp sub-panel?

  No. 6 AWG copper is rated for a maximum of 55–65 amps, which is well below the 100-amp requirement. Using undersized wire on a 100-amp feeder creates a serious fire hazard. The minimum for a true 100-amp feed with copper is 2 AWG (at 75°C terminals).

• What is the difference between welding cable and building wire of the same gauge?

  Welding cable uses ultra-fine stranded copper for flexibility and is insulated with rubber or EPDM for abrasion resistance, but it does not carry UL or NEC ratings for permanent building wiring. NEC building wire (THHN, XHHW, USE-2) uses coarser stranding and thermoplastic insulation rated for conduit and direct burial installation. The two are not interchangeable in code-governed installations.

• Does aluminum wire require a different gauge than copper for the same ampacity?

  Yes. Aluminum has higher resistivity than copper, so it requires a larger gauge for equivalent ampacity. As a general rule, aluminum wire must be two AWG sizes larger than copper to carry the same current. For example, where 2 AWG copper is used for a 100-amp feeder, 1/0 AWG aluminum would be the aluminum equivalent. Always use anti-oxidant compound on aluminum terminations and ensure connectors are rated for aluminum conductors (marked AL/CU).

• How many amps can 10 gauge wire handle in conduit?

  In free air or conduit with three or fewer current-carrying conductors, 10 AWG copper handles 30 amps (60°C) or 35 amps (75°C). With four to six conductors in the same conduit, NEC requires derating to 80%, reducing it to 24 amps (60°C) or 28 amps (75°C). Always check the actual installation conditions before sizing.