Add your appliances to calculate total circuit load in watts and amps — and instantly see if your breaker can handle it safely per NEC guidelines.
Free Tool · NEC 80% Rule · 120V & 240V
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Total Load (Amps)
\u2014
Total Watts
\u2014
Circuit Used
\u2014
of breaker capacity
Safe Remaining
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Circuit load vs. breaker capacity\u2014
\u25b2 80% NEC safe limit
Per-Appliance Breakdown
Summary
Total connected load
\u2014
Total amps drawn
\u2014
Breaker size
\u2014
NEC 80% limit
\u2014
Remaining safe capacity
\u2014
Circuit status
\u2014
How Electrical Load Is Calculated
Every circuit breaker has a maximum rated amperage — but the National Electrical Code (NEC) requires that continuous loads never exceed 80% of that rating. A continuous load is any device expected to run for 3 hours or more. This safety margin prevents wire and breaker overheating. Exceeding it won't always trip the breaker immediately — but it causes conductor insulation to degrade over time, which is a leading cause of residential electrical fires.
1 Watts \u2192 Amps
Amperage is what actually heats wires and trips breakers. Convert watts to amps by dividing by circuit voltage. All appliances on the same circuit share its amp capacity.
For continuous loads (running 3+ hours), NEC Article 210.20 limits safe load to 80% of breaker rating. A 20A breaker safely carries only 16A continuously \u2014 not 20A.
Divide your total amp draw by the breaker's rated amps. Below 80% is safe for continuous use. Between 80\u2013100% is a code violation for continuous loads. Over 100% will eventually trip the breaker.
Standard residential breaker sizes: 15A (lighting), 20A (kitchen/bath outlets), 30A (dryer/A/C), 40\u201350A (range/EV). Each circuit should have only one purpose on 30A+ breakers.
Next standard sizes:
15A \u2192 20A \u2192 30A
\u2192 40A \u2192 50A \u2192 60A
Dedicated circuits:
dryer, range, A/C,
dishwasher, EV charger
Dedicated Circuits for High-Draw Appliances
Any appliance drawing more than 7.5 amps continuously (about 900W on 120V) should ideally be on its own dedicated circuit. This includes refrigerators, microwaves, dishwashers, garbage disposals, and window A/C units. Sharing high-draw appliances on a single circuit is the #1 cause of nuisance breaker trips and is often a code violation in kitchens and bathrooms under NEC 210.11(C).
Example Project Scenarios
Click any scenario to load it into the calculator and see the full breakdown instantly.
Use these as starting points. Always check your appliance's nameplate label for the exact wattage \u2014 it's the only legally binding number for code calculations.
Appliance
Typical Watts
Voltage
Dedicated Circuit?
Refrigerator
100\u2013400W
120V
Recommended
Central A/C (3-ton)
3,000\u20135,000W
240V
Required
Window A/C
500\u20131,500W
120V
Recommended
Electric Clothes Dryer
4,000\u20136,000W
240V
Required (30A)
Washing Machine
350\u2013500W
120V
Recommended (20A)
Electric Range / Oven
6,000\u201312,000W
240V
Required (40\u201350A)
Dishwasher
1,200\u20132,400W
120V
Required (20A)
Microwave
600\u20131,200W
120V
Required (20A)
Water Heater (electric)
3,500\u20135,500W
240V
Required (30A)
EV Charger (Level 2)
7,200\u201311,500W
240V
Required (40\u201360A)
Space Heater
750\u20131,500W
120V
Recommended
Hair Dryer
1,200\u20131,875W
120V
No (short use)
LED Lighting (per bulb)
8\u201315W
120V
No
Desktop Computer
200\u2013400W
120V
No
Table Saw
1,500\u20132,000W
120V
Recommended (20A)
Frequently Asked Questions
A breaker trips when the total amp draw on that circuit exceeds its rated capacity, or when a short circuit or ground fault occurs. The most common cause of nuisance tripping is connecting too many high-draw appliances to a single circuit \u2014 particularly in kitchens, where a microwave, toaster, and coffee maker running simultaneously on the same 20A circuit can easily exceed 20A. The fix is to redistribute appliances across multiple circuits, or have an electrician add a dedicated circuit for high-draw appliances. Never replace a breaker with a larger one without an electrician verifying the wire gauge can handle the increased load \u2014 undersized wire is a fire hazard.
NEC Article 210.20(A) requires that for continuous loads \u2014 any load expected to run for 3 hours or more \u2014 the branch circuit rating must not be less than 125% of the continuous load. This is equivalent to saying continuous load must not exceed 80% of circuit capacity. The rule exists because electrical conductors and breakers generate heat when carrying current. Operating at or near 100% capacity for extended periods causes wires to overheat, damages insulation, and degrades the breaker itself over time. Even if a breaker doesn't trip immediately at 100% load, sustained overloading is a leading cause of residential electrical fires.
The NEC mandates dedicated circuits for several appliances: electric ranges and cooktops (40\u201350A, 240V), clothes dryers (30A, 240V), built-in dishwashers (20A, 120V), disposals (20A, 120V), microwave ovens (20A, 120V), refrigerators (15\u201320A, 120V recommended), and EV chargers (40\u201360A, 240V). NEC 210.11(C)(1) also requires at least two 20A small-appliance circuits for kitchen countertop outlets. Any appliance drawing more than 50% of a circuit's capacity should have its own dedicated circuit \u2014 especially motor-driven appliances that have high starting current surges above their running wattage.
Standard U.S. residential service is 120/240V single-phase. Standard outlets are 120V, using one hot leg plus a neutral wire. Large appliances \u2014 electric ranges, dryers, water heaters, central A/C, and EV chargers \u2014 run on 240V, using both hot legs from the panel. A 240V circuit at the same amperage delivers twice the power of a 120V circuit. For example, a 30A, 240V dryer circuit delivers up to 7,200W, whereas a 30A, 120V circuit would only deliver 3,600W. Never attempt to install 240V circuits yourself \u2014 they require a licensed electrician, a two-pole breaker, and specific wire gauge and outlet types.
The most reliable source is the nameplate label affixed to the appliance \u2014 usually on the back, bottom, or inside the door. It lists voltage, amperage, wattage (sometimes expressed as "VA"), and model number. If the label shows only amps (not watts), multiply amps by voltage to get watts: Watts = Amps \u00d7 Volts. For example, a label showing 9.5A at 120V means the appliance draws 1,140W. If the physical label is unreadable, look up the model number on the manufacturer's website \u2014 the product specification sheet always includes power consumption.
