Load Calculation for School

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WELLSEROUSKI

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Help please,
I have estimated a connected load of 104,036 VA for this building.
The service is 120/208
Using 220.86 nec what do you guys come up with? Somehow Im doing something wrong.
Thanks
 
WELLSEROUSKI said:
Help please,
I have estimated a connected load of 104,036 VA for this building.
The service is 120/208
Using 220.86 nec what do you guys come up with? Somehow Im doing something wrong.
Thanks
Click to expand...
If this is 3 phase system then you need to multiply your 208 X 1.73= 360. See if that helps
 
School Building

School Building

I did the calculation. I have a answer. But I woul like to see your calculation first.
 
100% of first 3va/sq ft
3*14,400 = 43,200
plus
75% of the next
3*14,400 = 43,200 * .75= 32,400
plus
25% of of the next
3*14,400 = 43,200 * .25= 10,800 43,200+32,400+10,800=86,400va

86,400va / 208 = 415.38 amps
 
WELLSEROUSKI said:
100% of first 3va/sq ft
3*14,400 = 43,200
plus
75% of the next
3*14,400 = 43,200 * .75= 32,400
plus
25% of of the next
3*14,400 = 43,200 * .25= 10,800 43,200+32,400+10,800=86,400va

86,400va / 208 = 415.38 amps
Click to expand...
Your still not giving us enough information. The above calculation appears to be load demand calculations of some sort, but you didn't state the type of building. The only 3-step load demand factoring which goes 100%-75%-25% is the optional method for school buildings. Is this correct?
 
School Calculation

School Calculation

Here is what I got using 220.86 Optional Method

104,036 va / 14,400 square feet = 7.3 va per square foot.

First 3 va per sq. ft. @ 100% 3 va x 14,400 sq ft = 43,200 va

7.3 va per sq ft - 3 va we just calculated leaves 4.3 va per sq ft

4.3 va x 14,400 sq ft x 75% = 46,440 va

43,200 va + 46,440 va = 89,640 va / (208 x 1.732) = 249 amps
for a three phase system.
 
HEYDOG said:
Here is what I got using 220.86 Optional Method

104,036 va / 14,400 square feet = 7.3 va per square foot.

First 3 va per sq. ft. @ 100% 3 va x 14,400 sq ft = 43,200 va

7.3 va per sq ft - 3 va we just calculated leaves 4.3 va per sq ft

4.3 va x 14,400 sq ft x 75% = 46,440 va

43,200 va + 46,440 va = 89,640 va / (208 x 1.732) = 249 amps
for a three phase system.
Click to expand...
That's not how 220.86 works. See below...
104,036 va / 14,400 square feet = 7.3 va per square foot. (copied from your post, not verified)​
The above qualifies for 75% demand.
104,036VA ? 75% = 78,027VA
78,027VA ? (3 ? 120V) = 217A​
Note 3 ? 120 = √3 ? 208
 
School Calculation

School Calculation

I totally disagree with you. Reread table 220.86 first 3va per square foot @ 100%; next 17 va per sq ft @ 75% anything over 20va per sq ft @ 25%. This is the way that I have seen in Mike Holts Books and Tom Henry's and other well known Instructors. If this is wrong than someone needs to address it.
Not being a smart alec. Just making a statement.
 
WELLSEROUSKI said:
100% of first 3va/sq ft
3*14,400 = 43,200
plus
75% of the next
3*14,400 = 43,200 * .75= 32,400
plus
25% of of the next
3*14,400 = 43,200 * .25= 10,800 43,200+32,400+10,800=86,400va

86,400va / 208 = 415.38 amps
Click to expand...

Assuming what you did is correct, you forgot the sqrt of 3.

86.4 kva/(.208 x 1.73)= 240 amps
 
HEYDOG said:
I totally disagree with you. Reread table 220.86 first 3va per square foot @ 100%; next 17 va per sq ft @ 75% anything over 20va per sq ft @ 25%. This is the way that I have seen in Mike Holts Books and Tom Henry's and other well known Instructors. If this is wrong than someone needs to address it.
Not being a smart alec. Just making a statement.
Click to expand...
My bad... you are correct. I was looking at the imperial (ft) column only, where it does not say "First" and "plus" :rolleyes:
 
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