{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"circuit-load"},"result":{"entity_type":"calculator","id":"circuit-load","calculator_id":"circuit-load","canonical_url":"https://tttkmbb.com/energy/circuit-load","name":"Circuit Load Calculator","title":"Circuit Load Calculator – Amps, Breaker Utilisation and Recommended Breaker Size from Appliance Watts (NEC 80 % Rule)","category":"energy","category_name":"Home Energy & Electrical","tool_name":"calculate_circuit_load","featured_mcp_tool":false,"description":"Adds up the appliance wattages on one branch circuit, converts them to amperes at the given voltage and power factor, compares the load with the breaker rating (applying the NEC 80 % continuous-load limit when requested) and recommends the smallest standard breaker size that fits.","use_when":"You want to know whether a set of appliances will trip a breaker, how much capacity a circuit has left, or which standard breaker size a load needs.","do_not_use_when":"You need conductor sizing or voltage drop on a long run (use wire-voltage-drop), motor inrush or generator sizing (use generator-sizing), or a whole-service load calculation per NEC Article 220; local code and a licensed electrician decide the installed breaker.","inputs":[{"name":"voltage_v","label":"Circuit voltage","type":"number","unit":"V","required":false,"default":230,"min":12,"max":1000,"description":"Nominal circuit voltage: 230 (Europe, Australia), 120 or 240 (North America).","example":230},{"name":"breaker_amps","label":"Breaker rating","type":"number","unit":"A","required":false,"default":16,"max":1000,"exclusive_min":0,"description":"Rating of the circuit breaker or fuse protecting the circuit.","example":16},{"name":"loads_w","label":"Appliance loads","type":"number_list","unit":"W","required":true,"description":"Rated power of each appliance on the circuit in watts, comma-separated (use the nameplate value).","example":[2000,800,500]},{"name":"continuous_load","label":"Continuous load","type":"boolean","required":false,"default":false,"description":"true when the load runs 3 hours or more at a time (heaters, lighting, EV chargers): NEC 210.20(A) then limits it to 80 % of the breaker rating.","example":false},{"name":"power_factor","label":"Power factor","type":"number","required":false,"default":1,"max":1,"exclusive_min":0,"description":"Power factor of the loads: 1 for resistive heaters and kettles, 0.8–0.95 for motors and electronics.","example":1}],"outputs":[{"name":"total_watts","label":"Total load","type":"number","unit":"W","decimals":1,"description":"Sum of loads_w."},{"name":"total_amps","label":"Total current","type":"number","unit":"A","decimals":2,"description":"total_watts / (voltage_v × power_factor)."},{"name":"breaker_capacity_percent","label":"Breaker utilisation","type":"number","unit":"%","decimals":2,"description":"total_amps / breaker_amps × 100."},{"name":"max_continuous_amps","label":"Continuous limit (80 %)","type":"number","unit":"A","decimals":2,"description":"0.8 × breaker_amps, the NEC limit for continuous loads."},{"name":"within_limit","label":"Within limit","type":"boolean","decimals":4,"description":"true when total_amps ≤ breaker_amps (non-continuous) or ≤ 80 % of it (continuous)."},{"name":"headroom_w","label":"Headroom","type":"number","unit":"W","decimals":0,"description":"Watts that can still be added before the applicable limit; negative when over the limit."},{"name":"recommended_breaker_amps","label":"Recommended breaker","type":"integer","unit":"A","decimals":0,"description":"Smallest standard size (10, 13, 15, 16, 20, 25, 30, 32, 40, 50, 63 A) whose limit covers the load; absent when the load exceeds 63 A."}],"input_schema":{"type":"object","properties":{"voltage_v":{"description":"Nominal circuit voltage: 230 (Europe, Australia), 120 or 240 (North America). Unit: V.","type":"number","minimum":12,"maximum":1000,"default":230,"examples":[230],"x-unit":"V"},"breaker_amps":{"description":"Rating of the circuit breaker or fuse protecting the circuit. Unit: A.","type":"number","maximum":1000,"exclusiveMinimum":0,"default":16,"examples":[16],"x-unit":"A"},"loads_w":{"description":"Rated power of each appliance on the circuit in watts, comma-separated (use the nameplate value). Unit: W.","type":"array","items":{"type":"number"},"minItems":1,"examples":[[2000,800,500]],"x-unit":"W"},"continuous_load":{"description":"true when the load runs 3 hours or more at a time (heaters, lighting, EV chargers): NEC 210.20(A) then limits it to 80 % of the breaker rating.","type":"boolean","default":false,"examples":[false]},"power_factor":{"description":"Power factor of the loads: 1 for resistive heaters and kettles, 0.8–0.95 for motors and electronics.","type":"number","maximum":1,"exclusiveMinimum":0,"default":1,"examples":[1]}},"additionalProperties":false,"required":["loads_w"]},"output_schema":{"type":"object","properties":{"total_watts":{"description":"Sum of loads_w. Unit: W.","type":"number","x-unit":"W"},"total_amps":{"description":"total_watts / (voltage_v × power_factor). Unit: A.","type":"number","x-unit":"A"},"breaker_capacity_percent":{"description":"total_amps / breaker_amps × 100. Unit: %.","type":"number","x-unit":"%"},"max_continuous_amps":{"description":"0.8 × breaker_amps, the NEC limit for continuous loads. Unit: A.","type":"number","x-unit":"A"},"within_limit":{"description":"true when total_amps ≤ breaker_amps (non-continuous) or ≤ 80 % of it (continuous).","type":"boolean"},"headroom_w":{"description":"Watts that can still be added before the applicable limit; negative when over the limit. Unit: W.","type":"number","x-unit":"W"},"recommended_breaker_amps":{"description":"Smallest standard size (10, 13, 15, 16, 20, 25, 30, 32, 40, 50, 63 A) whose limit covers the load; absent when the load exceeds 63 A. Unit: A.","type":"integer","x-unit":"A"}}},"formula":"total_watts = Σ loads_w; total_amps = total_watts / (voltage_v × power_factor); breaker_capacity_percent = total_amps / breaker_amps × 100; max_continuous_amps = 0.8 × breaker_amps; limit = continuous_load ? max_continuous_amps : breaker_amps; within_limit = total_amps ≤ limit; headroom_w = (limit − total_amps) × voltage_v × power_factor; recommended_breaker_amps = min standard size S with total_amps ≤ S × (continuous_load ? 0.8 : 1)","method":"Single-phase circuit. NEC 210.20(A) requires the overcurrent device to be rated at least 125 % of a continuous load (equivalently the load ≤ 80 % of the rating); non-continuous loads may use the full rating. The standard-size list mixes IEC 60898 (10, 13, 16, 20, 25, 32, 40, 50, 63 A) and North American (15, 20, 30, 40, 50 A) ratings; choose the ones sold in your region.","sources":[{"name":"NFPA 70 – National Electrical Code (Article 210, Branch Circuits)","url":"https://www.nfpa.org/codes-and-standards/nfpa-70-standard-development/70","type":"standard","retrieved_at":"2026-09-24"},{"name":"Wikipedia – National Electrical Code","url":"https://en.wikipedia.org/wiki/National_Electrical_Code","type":"reference","retrieved_at":"2026-09-24"},{"name":"Wikipedia – Circuit breaker","url":"https://en.wikipedia.org/wiki/Circuit_breaker","type":"reference","retrieved_at":"2026-09-24"}],"freshness":{"type":"static","max_age_seconds":null,"note":"Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output."},"examples":[{"name":"230 V, 16 A breaker, 2000 + 800 + 500 W (non-continuous)","inputs":{"voltage_v":230,"breaker_amps":16,"loads_w":[2000,800,500]},"expected":{"total_watts":3300,"total_amps":14.35,"breaker_capacity_percent":89.67,"max_continuous_amps":12.8,"within_limit":true,"headroom_w":380,"recommended_breaker_amps":15},"url":"https://tttkmbb.com/api/v1/calculate/circuit-load?voltage_v=230&breaker_amps=16&loads_w=2000%2C800%2C500"},{"name":"Same loads running continuously","inputs":{"voltage_v":230,"breaker_amps":16,"loads_w":[2000,800,500],"continuous_load":true},"expected":{"total_amps":14.35,"within_limit":false,"headroom_w":-356,"recommended_breaker_amps":20},"url":"https://tttkmbb.com/api/v1/calculate/circuit-load?voltage_v=230&breaker_amps=16&loads_w=2000%2C800%2C500&continuous_load=true"}],"faq":[{"q":"What is the 80 % rule?","a":"NEC 210.20(A) sizes the breaker at 125 % of any load expected to run for 3 hours or more, so continuous loads may use only 80 % of a breaker's rating: 12 A on a 15 A circuit, 16 A on a 20 A circuit."},{"q":"Can I install the recommended breaker myself?","a":"The breaker protects the wiring, so it may only be upsized if the conductors are rated for it (e.g. 2.5 mm² / 12 AWG for 20 A). Have an electrician verify conductor size and local code."},{"q":"Should I use rated or measured watts?","a":"Use nameplate ratings for a conservative check; measured draw is usually lower (a 2,000 W kettle draws its full rating, a 800 W microwave draws about 1,200 W input)."}],"tags":["circuit load","breaker size","amps from watts","80 percent rule","will it trip the breaker","nec 210"],"related":[{"calculator_id":"wire-voltage-drop","reason":"Voltage drop and conductor size for the same current."},{"calculator_id":"electric-power","reason":"Watts, volts and amps of a single appliance."},{"calculator_id":"generator-sizing","reason":"Generator capacity for the same loads including motor starting."}],"links":{"html":"https://tttkmbb.com/energy/circuit-load","markdown":"https://tttkmbb.com/energy/circuit-load.md","json":"https://tttkmbb.com/energy/circuit-load.json","api":"https://tttkmbb.com/api/v1/calculate/circuit-load","schema":"https://tttkmbb.com/api/v1/calculators/circuit-load","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-24"},"timestamp":"2026-09-24T03:45:02Z","next_actions":[{"tool":"run_calculator","calculator_id":"circuit-load","reason":"Run Circuit Load Calculator with the inputs above."}],"links":{"markdown":"https://tttkmbb.com/energy/circuit-load.md"}}