A case study of main service short time demand intervals

Abstract

A new section was added to the 1990 edition of the National Electrical Code (NEC). The section presented an optional method to calculate the size of a new restaurant's service entrance and main distribution panel. In most cases application of the optional method resulted in reduction in service entrance and main panel sizes when compared to standard methods. Some engineers, end users, and others expressed concern about this reduction in service entrance size especially when considering the high electrical demands associated with starting-up a restaurant when it opens for the day. A restaurant in Indiana, USA, was instrumented for a field test of cooking equipment. This test arrangement was utilized to collect one minute demand interval data for several weeks. The data was recorded during the summer when the restaurant annual peak demand occurred and during the time of the day when the peak demand usually occurred. The results of the case study show the relationship between one minute demands, 15 minute demands, and other time intervals. Continuous loads as defined by the NEC are discussed with respect to the one minute demand data. Associations with protective device time-current curves are also explored. It also recommends what additional research is necessary to obtain data and establish indisputable and conclusive results.<>