A demand factor of ___% may be applied to the nameplate ratings of four or more fastened-in-place appliances in a one-family dwelling.

• A. 50
• B. 80
• C. 75
• D. 90

Answer: (C)

When sizing a dwelling’s electrical service, you don’t assume every fixed appliance will draw its full nameplate power at the same time. Demand factors adjust the combined load to reflect typical usage patterns. For four or more fastened-in-place appliances in a one-family dwelling, you may apply a 75% factor to the sum of their nameplate ratings. This means you add up the ratings of those appliances and multiply by 0.75 to get the demand load contributed by them. The rest of the service load (lighting, outlets, etc.) is added on top as appropriate. If you have fewer than four such appliances, different factors apply per the code. For example, four fixed appliances totaling 12 kW would contribute 9 kW to the load (12 kW × 0.75). The options of 50%, 80%, or 90% would not align with this standard factor, which is set at 75% to balance safety with typical usage.