Optional method demand calculation

Status
Not open for further replies.
B

bigpapa400lb

Member
A single family dwelling is supplied with a 120/240 volt, single phase, three wire service. This dwelling has 1,800 square feet, a total appliance load of 16,000 VA, 8,000 VA of air conditioning and 15,000 VA of electrical heating. Using the optional method, what is the total computed load for this dwelling?

The answer I get is 20,260va .

The answer key says 26,110va.
 
Hmmm, I get 29.6 KVA. You can ignore the air conditioning since the heating is higher. Are you sure you typed the numbers right? This is pretty simple:

1800 ft2 * 3 = 5,400
+ 16,000

Take first 10 KVA at 100%, and the remaining at 40%.
Add the Heating KVA, and you're done.
 
220.82

B
1) 3va/sq ft -> 1800*3=5400
2) appliance and laundry 1500 x 3 = 4500
3) no appliances listed
4) no motors listed

total = 9900

100% of 1st 10kva + 40% of remainder = 9900


C
heating at 100% = 16000

total = 25900

hmm, did I make a math error ?
 
Mark, you left out the two small appliance circuits and the laundry circuit.

Here is how the answer key's author came to the value of 26,110:
  1. 1800 * 3 = 5,400
  2. Add 4,500 for the three required circuits.
  3. Add 16,000 for the known appliance load.
  4. That gives you 25,900.
  5. Take 100% of the first 10KVA and 40% of the rest, and you now have 16,360.
  6. Take 65% of the heating load, per 220.82(C)(4), and that adds 9,750 to the party.
  7. Add 16,360 + 9,750 and you get 26,110.
 
Status
Not open for further replies.
Top