Circuit Amps
15.0 A
Load
75%
Required Breaker
20A
Status
OK
15.0 A
75%
20A
1.0 A
Load is 75% of breaker rating. Within NEC 80% continuous load limit.
Inputs
Result
Amps = 1800 / 120 = 15A. NEC 80% limit for 20A breaker = 16A. Load is 15/20 = 75%. Remaining = 16 - 15 = 1A. Wire gauge 12 AWG matches 20A breaker.
Inputs
Result
Amps = 3600 / 240 = 15A. NEC 80% limit for 20A breaker = 16A. Load is 15/20 = 75%. 12 AWG wire is correct for 20A.
The NEC 80% rule (Article 210.20) states that a circuit breaker should not be loaded beyond 80% of its rated capacity for continuous loads. A 20A breaker can safely carry 16A continuously (20 x 0.80 = 16A).
| Breaker Size | Max Continuous Load (80%) | Max Non-Continuous (100%) |
|---|---|---|
| 15A | 12A | 15A |
| 20A | 16A | 20A |
| 30A | 24A | 30A |
| 40A | 32A | 40A |
| 50A | 40A | 50A |
Divide total wattage by circuit voltage to get amperage (Amps = Watts / Volts). Then divide by 0.80 for the NEC safety margin and round up to the next standard breaker size (15A, 20A, 30A, 40A, or 50A).
A 20A breaker requires minimum 12 AWG wire. Wire gauge requirements per NEC: 15A = 14 AWG, 20A = 12 AWG, 30A = 10 AWG, 40A = 8 AWG, 50A = 6 AWG. Using undersized wire is a fire hazard.
| Breaker Size | Min Copper AWG | Min Aluminum AWG | Common Uses |
|---|---|---|---|
| 15A | 14 AWG | 12 AWG | Lighting, general outlets |
| 20A | 12 AWG | 10 AWG | Kitchen, bath, garage outlets |
| 30A | 10 AWG | 8 AWG | Dryer, water heater |
| 40A | 8 AWG | 6 AWG | Range, large appliance |
| 50A | 6 AWG | 4 AWG | Sub-panel, EV charger |
No. 14 AWG wire is only rated for 15A circuits. Installing a 20A breaker on 14 AWG wire is a code violation and fire hazard. The wire could overheat before the breaker trips. Always match wire gauge to breaker size.
NEC allows up to 13 outlets on a 20A circuit (180 VA per outlet, 20A x 120V = 2400 VA, 2400/180 = 13). For kitchens and bathrooms, NEC requires dedicated 20A circuits with fewer outlets.
| Location | Circuit Size | Max Outlets (NEC) | Practical Limit |
|---|---|---|---|
| General rooms | 15A or 20A | 10–13 | 8–10 |
| Kitchen countertop | 20A (dedicated) | 13 | 4–6 (high load) |
| Bathroom | 20A GFCI | 13 | 2–4 |
| Garage | 20A GFCI | 13 | 4–6 |
| Laundry | 20A (dedicated) | 1 | 1 (washer only) |
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Last Updated: Mar 9, 2026
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