Largest Motor for Standar Calculation

[Deanna123]

Using Standard calculations in article 220 there is nothing I can find that requires the largest motor in the calculation. 220.50 says "Motor loads shall be calculated in accordance with 430.24, 430.25 and 430.26 and with 440.6 for hermetic refrigerant motor compressors". There is no requirement in the refered articles; however ther is a largest motor requirement in 440.7. Does anyone have any input on this.

 

[rbalex]

I may be misunderstanding your question, but Section 430.24 requires the largest motor's current to be included at 125% in the calculation for conductor ampacity. Section 440.7 specifically notes the basis for determining the "largest" motor as it applies to certain HVAC loads for Section 430.24 and various other Art 430 applications.

 

[Deanna123]

I am doing a standard calculation for a multi-family dwelling and a former inspector says that I have to include the largest motor for this calculation to be derated at 25% which happens to be the gabage disposal. I can not find this requirement in the 2008 NEC.