Do I really need to do a load calculation for every job?
Yes, NEC Article 220 requires load calculations for service entrance sizing and panel load determinations. This ensures electrical safety and code compliance for residential installations. See also our calculate Demand Factor Total Demand Load.
Why is my calculated load so much higher than my actual electric bill?
Load calculations determine maximum simultaneous demand based on NEC requirements, not actual usage. The calculation includes safety factors and considers worst-case scenarios that rarely occur in real life.
What's the difference between connected load and calculated load?
Connected load is the sum of all electrical equipment ratings. Calculated load applies NEC demand factors and diversity factors to determine the actual expected maximum demand on the electrical system.
Can I use the optional method for all residential load calculations?
The optional method (NEC 220.82) can only be used for single-family dwellings and individual dwelling units with specific conditions. It often results in smaller service sizes than the standard method.
How do I handle a house with both gas and electric appliances?
Only include electric appliances in your load calculation. Gas appliances (gas range, gas dryer, gas water heater) should be entered as 0 VA since they don't contribute to electrical load.
What's the deal with 125% for continuous loads?
NEC requires continuous loads to be calculated at 125% of their rating for conductor and overcurrent protection sizing. This accounts for loads operating for 3 hours or more continuously.
Do electric vehicle chargers count as appliance loads?
Yes, EV chargers are considered fixed appliances and must be included in load calculations. They typically range from 3.8kW (Level 2) to 11.5kW for residential installations.
Can I count diversity factors between different panels?
Diversity factors are already built into NEC demand factor tables. Additional diversity between panels may be considered by engineers but should follow local code requirements and engineering judgment. You might also find our Raceway Fill Calculator useful.