Methodology
Our calculators are based on NEC 2023. Check the code edition and amendments adopted in your jurisdiction.
How calculations are checked
We use a versioned calculation specification, reviewed against NEC 2023 through NFPA Free Access. Development tests compare 154 complete numerical and refusal cases, including the Annex D D2(a), D2(b) and D2(c) load examples. Public manufacturer information and worked examples provide supplemental checks where their models match. External online-tool measurements of every combined branch have not been completed.
The calculations have not been independently reviewed by a licensed electrician. Automated tests verify the implemented specification; they do not verify field data, local acceptance or installation conditions.
Interpretations and model limits
For 220.83(A), existing HVAC enters the general pool as fixed appliances. For 220.83(B), heat-pump heating uses full compressor and supplemental input except confirmed interlock; this is a conservative adopted interpretation. 220.87 kW assumes power factor 1.0, and highest-leg A is a capacity-equivalent comparison. Voltage drop uses 75°C pure resistance, not an AC impedance model. Every tool describes its own exclusions.
Report a discrepancy
Contact: support@electricalloadcalcs.com Include the tool, method, code edition, non-personal input numbers, expected result and your reference identifier. Do not send customer addresses or private project documents. A confirmed calculation error requires a fix and regression example, or temporary tool suspension while reviewed.