What size wire do I need for a 20 amp breaker?

12 AWG copper or 10 AWG aluminum, per NEC Table 310.16 at the 75°C column. The equipment grounding conductor is 12 AWG copper per NEC Table 250.122.

What is the maximum continuous load on a 20 amp breaker?

16 amps. NEC 210.19(A)(1) and 210.20(A) require the circuit to be rated at 125% of a continuous load — one that runs for three hours or more — which works out to 80% of the breaker rating available for continuous use. Non-continuous loads may use the full 20 A.

What size ground wire for a 20 amp breaker?

12 AWG copper or 10 AWG aluminum, from NEC Table 250.122. The table lists maximum overcurrent device ratings, so you round up to the next listed row. If the circuit conductors are upsized for voltage drop, NEC 250.122(B) requires the ground to be upsized proportionally too.

Can I use 12 AWG NM-B cable on a 20 amp breaker?

Yes. NEC 334.80 requires NM-B ampacity to be taken from the 60°C column of Table 310.16, where 12 AWG copper is rated 20 A. That is why NM-B sometimes needs a larger conductor than THHN in conduit for the same breaker.

20 Amp Breaker Wire Size

Copper Wire

12 AWG

Aluminum Wire

10 AWG

Ground (Copper)

12 AWG

Single-pole · 120 V · Max continuous load 16 A · NEC Tables 310.16 and 250.122

20 Amp Circuit — Specification Summary

Item	Value
Breaker type	Single-pole, 120 V
Recommended copper conductor	12 AWG
Recommended aluminum conductor	10 AWG
Minimum per NEC Table 310.16, 75°C	14 AWG copper (20 A)
Minimum NM-B cable, 60°C column	12 AWG copper (20 A)
Equipment grounding conductor	12 AWG copper / 10 AWG aluminum (NEC Table 250.122)
Maximum continuous load (125% rule)	16 A
Maximum non-continuous load	20 A

Recommended conductor sizes follow the 75°C column of NEC Table 310.16, the column that matches the termination rating of virtually all modern breakers and lugs (NEC 110.14(C)).

Common Uses for 20 A Circuits

Kitchen small-appliance circuits, bathroom receptacles, laundry, garage and outdoor receptacles, workshop tools

What a 20 Amp Breaker Powers

Load	Notes
Kitchen small-appliance circuits	Two required — NEC 210.52(B)
Bathroom receptacle circuit	Dedicated 20 A required — NEC 210.11(C)(3)
Laundry receptacle circuit	Dedicated 20 A required — NEC 210.11(C)(2)
Dishwasher	Commonly 15 A, often wired 20 A
Garbage disposal	Typically 15 A or 20 A
Microwave (built-in)	Dedicated 20 A circuit

Always size a circuit from the equipment nameplate or a load calculation, not from a general table. Air conditioners and heat pumps in particular carry a minimum circuit ampacity (MCA) and maximum overcurrent protective device (MOCP) rating that override the general rules.

NEC requirements for this circuit

20 A on 12 AWG copper is the workhorse circuit of modern residential wiring. NEC 240.4(D)(5) caps 12 AWG copper at 20 A despite the 25 A figure in Table 310.16.

GFCI required for all kitchen countertop, bathroom, garage, outdoor, basement, and laundry receptacles (NEC 210.8(A)). AFCI required in most dwelling rooms (NEC 210.12(A)).

Voltage Drop by Distance — 12 AWG Copper at 20 A

One-way run	Drop	% of 120V	Verdict
25 ft	1.98 V	1.6%	Within the 3% branch-circuit target
50 ft	3.96 V	3.3%	Over 3% — upsize one gauge
75 ft	5.94 V	4.9%	Over 3% — upsize one gauge
100 ft	7.92 V	6.6%	Well over 3% — upsize two gauges or more
150 ft	11.88 V	9.9%	Well over 3% — upsize two gauges or more
200 ft	15.84 V	13.2%	Well over 3% — upsize two gauges or more

Single-phase, 120V, full 20 A load, 1.98 Ω/1000 ft DC resistance (NEC Chapter 9, Table 8) at 75°C terminations. NEC 210.19(A) Informational Note recommends keeping branch-circuit drop at or below 3%, and 5% total across feeder plus branch circuit. See the voltage drop formula for the arithmetic.

The 80% rule: a continuous load is one expected to run for three hours or more — EV chargers, electric heat, and most commercial lighting. NEC 210.20(A) requires the overcurrent device to be rated at not less than 125% of that continuous load, which leaves 16 A usable on a 20 A breaker. A breaker that trips after an hour or two under a steady load is usually a continuous-load sizing mistake, not a faulty breaker.

Other Breaker Sizes

15A 20A 30A 40A 50A 60A 100A 200A

Wire size for 20 amps — full page → 12 AWG full specifications → NEC Table 250.122 — ground wire size → NEC Table 310.16 — conductor ampacity → Wire size calculator →