Designing an electrical panel involves multiple calculations, including load estimation, breaker sizing, conductor sizing, and voltage drop analysis. Calculate service entrance sizing, panel loads, demand factors, and ensure NEC Article 220 compliance. 42 (demand factors: first 3000 VA at 100%, remainder at 35%), 210. 20 (A) (continuous loads. Summary: Residential Electrical Load Calculator, Online and Interactive provides accurate main service panel load calculations. Short Explanations to help you get started.