While there's no definitive study proving this as a universal truth, it's a reasonable generalization that many residential services often operate below 75% of their calculated load, but it's NOT accurate to say most never exceed it. Here's why

Arguments for why it can be true:
Diversity Factor

Load calculations (like those in the NEC Article 220) include diversity factors. These factors acknowledge that not all appliances and loads will be operating at their maximum rated power simultaneously. For example, you're unlikely to be running your oven, dryer, electric water heater, and all your lights at full capacity at the exact same moment.

Occupancy Patterns

Many homes are unoccupied during the day (when people are at work or school), leading to lower overall loads during peak daylight hours.

Energy Efficiency

Modern appliances are generally more energy-efficient than older models. LED lighting, energy-star appliances, and more efficient HVAC systems all contribute to lower overall energy consumption.

Behavioral Factors

People are often conscious of energy usage and may consciously avoid running multiple high-draw appliances at the same time to save money.

Oversizing

Electrical services are often sized based on worst-case scenarios and future expansion plans, leading to capacity exceeding actual needs.

Climate

Mild climates reduce the reliance on heating and air conditioning, lowering peak demand.

Arguments against why it's NOT always true (and where it fails)



Cold Climates with Electric Heating

In regions with cold winters and electric baseboard heat, resistance heating can cause substantial peak demand. A prolonged cold snap can easily push a dwelling above 75% of calculated load for extended periods.

Hot Climates with Air Conditioning

Similar to cold climates, hot climates with central air conditioning can see very high, sustained loads, especially during heat waves. Especially during peak times when the grid is under the most strain.

Large Families

Homes with large families are more likely to have multiple high-draw appliances in use simultaneously (e.g., multiple showers, laundry, cooking, entertainment).

Electric Vehicle (EV) Charging

The increasing popularity of EVs is drastically changing residential load profiles. Charging an EV can add a significant, sustained load, potentially exceeding the typical "worst-case" scenario considered in traditional load calculations. If multiple EV's exist then this load is even more significant.

Home Businesses/Work from Home

The rise in remote work means that more people are using more electricity at home during the day. Computers, printers, multiple monitors, and other office equipment add to the load.

Specialty Loads

Hot tubs, swimming pool heaters, welders, large power tools, and other specialty equipment can dramatically increase peak demand.

Outdated Load Calculations

Calculations may not always account for the full array of modern appliances and devices used in a home.

Weekend Peaks

Weekend use and special events (parties, holidays) can lead to high, simultaneous loads.

In conclusion

The 75% rule is a generalization that is more likely to hold true for smaller homes, homes with conservative electricity usage, and homes in moderate climates. However, it's not a reliable assumption for all dwellings.

Specifically, consider the presence of electric heating, air conditioning, EV charging, large families, home businesses, and specialty loads. Therefore, it's important to carefully consider these factors when evaluating service loads and sizing electrical equipment.Rather than relying on a fixed percentage, a more prudent approach involves performing a thorough load calculation based on the specific characteristics of the dwelling and the likely usage patterns of the occupants. Flag for review