Electrical Load & Circuit Breaker Capacity
Calculate branch circuit electrical load in watts and amps. Prevents breaker trips with NEC 80% continuous load rule, wire gauge sizing.
Connected Devices on This Circuit
Select devices plugged into the same branch circuit breaker:
Circuit Capacity & Load Gauge
⚡ National Electrical Code (NEC) 80% Rule
For continuous loads running 3+ hours (e.g. space heaters, lighting, EV charging), NEC Article 210.19 requires circuits to not exceed 80% of rated breaker capacity:
• Max Safe Continuous Load: 16.0A (1,920 Watts)
• Absolute Instantaneous Trip Point: 20.0A (2,400 Watts)
Electrical Load Summary & Breaker Safety
⚠️ Decision Verdict: High Breaker Trip Risk!
Running these appliances simultaneously draws 22.5 Amps (2,700 Watts) on your 20-Amp breaker (112.5% load). The bimetallic thermal-magnetic element in your electrical panel will overheat and trip the circuit breaker within minutes to prevent wire insulation melting and house fire hazard. Move the space heater or microwave to a different branch circuit.
About this tool
How to use it
- Select your circuit voltage (120V standard North America, 240V heavy appliances/EV, or 230V UK/Europe).
- Choose your circuit breaker amp rating (15A general living, 20A kitchen/bath/garage, 30A dryer, 50A EV charger).
- Check all appliances and electronic devices currently plugged into or planned for this circuit branch.
- Add custom appliances by entering their wattage nameplate rating if not in the preset checklist.
- Review your total wattage, current draw in amps, capacity percentage, NEC 80% rule limit, and minimum wire gauge.
Why it matters
Circuit breakers protect in-wall electrical wiring from overheating and causing residential electrical fires. When homeowners plug multiple high-wattage heating elements (space heaters, hair dryers, microwaves, coffee makers) into the same branch circuit, the current draw exceeds the breaker's trip curve, cutting power or posing severe fire hazards.
When to use it
Use this calculator before plugging in a portable space heater, installing a portable AC unit, planning home workshop tools, setting up a cryptocurrency mining rig, or upgrading kitchen appliances.
Good to know
NEC 80% Rule: The National Electrical Code (NEC Article 210.19/210.20) mandates that any continuous electrical load (operating continuously for 3 hours or more) must not exceed 80% of the circuit breaker's rated capacity.
Common questions
What is the NEC 80% continuous load rule?
Under National Electrical Code (NEC) standards, circuits carrying continuous loads (loads sustained for 3 hours or more, such as space heaters or EV charging) must not exceed 80% of the breaker's rated amperage. A 15-amp breaker has an 80% continuous limit of 12 amps (1,440W at 120V); a 20-amp breaker has an 80% limit of 16 amps (1,920W at 120V).
Why does my space heater keep tripping the breaker?
Almost all portable electric space heaters draw 1,500 Watts on high, which pulls 12.5 Amps at 120V. On a 15A circuit (1,440W continuous safe capacity), the heater alone utilizes 83% of the circuit. Turning on a single lamp, computer, or TV pushes total load past 15A, tripping the thermal breaker.
Can I replace a 15-amp breaker with a 20-amp breaker?
No, never upgrade a circuit breaker without rewiring the circuit! 15-amp circuits are wired with 14 AWG copper wire. Installing a 20-amp breaker allows 20 amps through 14 AWG wire, causing the wires inside your walls to overheat and create an immediate house fire hazard. 20-amp breakers require thicker 12 AWG wire.
How do I find an appliance's wattage?
Look at the manufacturer's specification label stamped on the back or underside of the appliance. If the label lists Amps instead of Watts, multiply Amps by Volts (e.g., 10A × 120V = 1,200 Watts).
What wire gauge is needed for 30A and 50A circuits?
A 30-amp circuit (such as an electric clothes dryer or water heater) requires 10 AWG copper conductors. A 50-amp circuit (such as a Level 2 electric vehicle charger or electric kitchen range) requires 6 AWG copper conductors.