How the electrical load calculator works
Choose a method, verify its eligibility, and enter every applicable nameplate once. The optional methods combine floor-area and circuit allowances with appliance VA, apply a tiered demand calculation, then handle HVAC for the selected branch. The measured-demand method uses a qualified record and already calculated new loads.
220.82: min(G, 10,000) + 0.40 × max(G − 10,000, 0) + H. 220.83: min(G, 8,000) + 0.40 × max(G − 8,000, 0), with branch B HVAC added separately. 220.87: 1.25 × recorded maximum demand + calculated new loads.
Worked example
Existing dwelling, 220.83(B): 2,000 ft² × 3 = 6,000 VA; two small-appliance and one laundry circuit = 4,500 VA; existing appliances = 6,000 VA; new 48 A EVSE at 240 V = 11,520 VA. General pool = 28,020 VA. First 8,000 VA + 40% × 20,020 VA = 16,008 VA. Add 6,000 VA cooling, larger than heating: total 22,008 VA ÷ 240 V = 91.7 A. Compared with a confirmed 100 A service, remaining capacity is 8.3 A under this method.
NEC references
NEC 2023: 220.82; 220.83(A); 220.83(B); 220.87; 220.42; 220.57; 240.4; 230.90. These are reference identifiers, not reproduced code text. Read our methodology and verification limits.
Limitations
One dwelling unit and 120/240 V single-phase three-wire supply only. Service, feeder and protection capacity must be verified. No EMS discounts, multiple-service calculations or commercial loads. 220.83(A) treats existing HVAC as fixed appliances in the general pool; 220.83(B) heat-pump handling is a conservative adopted interpretation. Four or more independently controlled heaters are unsupported in branch B. Check local method acceptance and adopted edition.
For estimation only. Results compare loads under the selected NEC method; they do not guarantee permit approval or code compliance. Verify with your local adopted code and a licensed electrician.
FAQ
Which method is right for an EV addition?
For an existing dwelling, start with 220.83 and state whether HVAC is also being added. A qualified demand record can support 220.87 where allowed locally.
Is a 200 A panel label enough?
No. Verify effective service, relevant feeder conductor and protective-device capacity; a panel label alone does not establish the limit.
Is the EV charger multiplied by 125%?
In these optional methods it enters the general pool at nameplate VA. Under 220.87 its added load uses the greater of 7,200 VA or nameplate VA, with no second 125% factor here. Conductor sizing is a separate task.
Can I use my electricity bill’s kWh?
No. Energy totals are not maximum demand. The measured method requires a qualified annual or eligible continuous 30-day demand record.
Will this PDF guarantee a permit?
No. It records the selected method and inputs for review. Local amendments, installation conditions and reviewer requirements still apply.
Where are my project details stored?
Project name, address, preparer and license number stay in this page’s memory and the PDF you download. They are excluded from saved inputs, share links and analytics.