Sizing a disconnect for a combination load

[buckeyemurph]

I have a question with the description of sizing a disconnect in the 2005 code handbook. There is an example in the code in Article 430.110 that explains the process of calculating the HP size and the ampere rating. It states the the ampere rating must be no less than 115 percent and also have a HP rating not less than the combined load. Going through the example it shows that a 15HP disconnect is selected, but it doesn't meet the minimum 115% requirement of 61.3 amps. It then states to select the next larger size of 20HP which meets both the HP requirment and the full load rating of 53.3 amps? Shouldn't this be the 61.3 amp rating which in turn would require the selection of the 25HP rating??

 

[jtester]

I don't think you are comparing apples to apples. If a disconnect is rated for 20 hp it meets the 54x1.15 requirement. Note the 20 hp disconnect must have a FULL LOAD rating of 54 amps, that does not include the 1.15 multiplier, and equates to the 53.3 amps of full load in the original load calc.

Jim T