220.53

[charlie b]

1. In the intended context of the "75% demand factor for four or more appliances fastened in place," do any of the following meet the definition of appliance (i.e., can we include them in the 75% DF)?
   • Range hood fan.
   • Bathroom exhaust fan.
   • Garage door opener.
2. If the largest motor happens to be one of the four or more appliances, do we get to apply the 75% demand factor to the 25% factor that we have to add for the largest motor?

Regarding item 1, I can't think of a reason why not. But it just seems wrong to me.

Regarding item 2, I think not, but I can't see a clear answer in the code language.

 

[bphgravity]

1. Yes to all three appliances you listed.

2. No. 25% of the largest motor at 100% of the nameplate rating. Apply each requirement (section) separately.

 

[charlie b]

2. No. 25% of the largest motor at 100% of the nameplate rating. Apply each requirement (section) separately.

Let me further clarify the question. Suppose a fastened-in-place appliance (one of four) happens to also be the largest motor. The appliance load at 100% is 1000 VA. By the time the calculation is done, does it get counted as,

1. 1250 VA (125% of largest motor, and the 75% DF does not apply at all), or
2. 1000 VA (First take the 75% DF on the 1000 VA rating, then add 25% of the 1000 VA rating due to largest motor), or
3. 937.5VA (125% of largest motor, then apply the 75% DF).

 

[bphgravity]

The end result would be #2.

The appliance calculation would be 75% of 1000 VA + the 3 or more other applaiances.

Then you would have to add 25% to the largest motor appliance which would be 250 VA in addition to the appliance calculation.

For example. Say you have 4 appliances at 1000 VA each.

Solution: 1,000 VA x 4 = 4,000 x .75 = 3,000 VA applied to the feeder / service calculation.

Then you must add 25% of the largest motor (1000 VA) = 250 VA applied to the calculation.

For a total of 3,250 VA based on those two requirements.

(The 25% increase of the largest motor does not get included in the 75% demand allowance for the applainces.)

 

[charlie b]

Thanks, Bryan. That is how I saw it as well. I am reviewing design documents from another group, including a load calculation. They included the 25% large motor value within the total appliance load to which the 75% DF was then applied. It makes a very small difference in the result. But I wanted the process to be correct.