Standard Residential Calculation

[deputygrsmith]

I have book questions asking for standard calculations. My question is on the largest motor (25%) part. I can find no clear cut rule on this. The book chose to take 6000VA x 25% AC Unit on one question, and on another question, it ignores the 6000va and uses 2600va x 25% on for a water pump.

Is there a clear cut rule for selecting the "proper" largest motor for both phase conductor and Neutral conductor?

Thank You.

 

[celtic]

I have book questions asking for standard calculations. My question is on the largest motor (25%) part. I can find no clear cut rule on this. The book chose to take 6000VA x 25% AC Unit on one question, and on another question, it ignores the 6000va and uses 2600va x 25% on for a water pump.

Is there a clear cut rule for selecting the "proper" largest motor for both phase conductor and Neutral conductor?

Thank You.

What book is it that you are using?

To answer the question " Is there a clear cut rule ", yes.

Section 220.50, by referenceing sections in 430(specifically 430.24) requires 25% of the largest motor full-load current (FLC) to be part of the feeder load.

Above, from the book I use

 

[snewman24]

When I recently took my journeyman test prep class we used Tom Henry's Calculations & Exam Questions book. He shows that when using the General Method, that if you have two noncoincident loads (not in use at the same time) such as heating loads and cooling loads, that you use the largest load for the calculations and omit the other. If the smaller load you omitted happens to be the air conditioning, which is also the largest motor, you disregard it as the largest motor, and use the second largest motor, which in your case may have been the water pump motor.