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In some cases, specific equipment requirements may dictate larger or smaller sizes, based on alternate load requirements or alternative overcurrent device requirements.
An example of alternate load requirements can be seen in an appliance or a tool that has a duty cycle and only operates half the time. In that case, a smaller conductor may be acceptable because the heat produced in that conductor will be based on a different condition than a load that persists continuously or over a longer period of time.Article 630: Welders
A good example of this is in Article 630, which deals with welders. The requirements for welders sometimes allow decreasing the size of the conductor below the nameplate rating of the welder and increasing the size of the overcurrent device beyond the nameplate rating of the welder, based on the way that a welder actually operates.
Alternate overcurrent device requirements might also vary for some types of circuit or load. In some situations, an overcurrent device might be required that has a rating greater than the ampacity of the selected conductor.
If the conductor cannot be protected at that rating in accordance with Article 240, a larger conductor may have to be chosen. In other cases, such as motors (especially fire pump motors), overcurrent devices must be larger than the minimum conductor size, and the conductor is not required to be increased in size.
© Hughes Associates,Inc. 2012