Largest Motor Load

[carter3933]

I am using Stallcup's study guide. In the chapter on residential calculations, under the section Largest Motor Load, it says:

"The motor's total full-load current rating shall be calculated at 25 or 125 percent per 220.14(c) and 220.50, which is required per 430.24 and 430.25, for calculating the load of one or more motors with other loads"

I can't find where the 25 comes from.

Does anybody know? I've looked in code book and in this forum.

Thanks,
Ron

 

[FrancisDoody]

Stallcup's Addition Method

Stallcup's Addition Method

I believe that if you look at the method that Stallcup uses in adding the largest motor you will see where the 25% vs 125% difference comes from. They take the VA of each appliance and add them together, then go back and fine the largest motor and then add an additional 25% from that motor to arrive at the total VA.

Example

Range load 12000 VA
Dryer Load 5000 VA
Disposal Load 900 VA
Compactor Load 1200 VA
Dishwasher load 1600 VA

Largest Motor 1200 VA X 25% = 400VA

Where you could just have done the compactor at 125% and been done with it.

 

[carter3933]

Thanks for the help