Another of these factors is equipment nameplate rating vs. actual load. For numerous applications, there are provisions in the National Electric Code (NEC) to assist in this reconciliation such as the demand factors listed in Tables 220.11 and 220.13 of the current NEC (Figure 1). Whether through the NEC, practical experience, or a combination of the two, many have found the demand to be consistently 25% to 50% of the nameplate value.
Also, with changes in the use of technology and more concentrated occupancy rates, there has been an upward trend in the "watts per square foot" design load. Whereas general purpose power might have been 1 to 3 W/sq ft in the 1970s, it now might be more in the range of 5 to 15 W/sq ft.