How many watts would 20 duplex receptacles add if they were not included in the original demand calculation?

When calculating the additional demand for electrical receptacles, the National Electrical Code (NEC) provides guidelines on how to determine the expected load for these devices. For residential applications, the demand for each duplex receptacle is typically considered as a minimum of 180 watts per receptacle if not accounted for in the original demand calculation.

In this scenario, with 20 duplex receptacles, the total additional demand would be calculated as follows:

20 receptacles x 180 watts each = 3600 watts.

However, the NEC allows electricians to take a more nuanced approach for general-use receptacles when included in a demand load calculation. Only a certain percentage of the total receptacles may need to be considered for calculations, based on a formula that allows for diversity in use.

For example, if the demand calculated is based on a typical setup where only a fraction (typically the first 10) of these receptacles might receive full load, the calculation could yield an overall lower requirement.

In the context of this question, if one considers a unique setup allowing for maximum utility, and the more common usage would imply that fewer would likely be drawing a full load at any one time, the demand would lean toward 1/2 of this maximum usage for practical