Im back with another problem.

[kefox81]

Hey everyone. I am back with more problems. I was doing good for a while but I have ran into another wall so I thought I would post.

What would be the minimum general lighting demand for a 2000 square foot residence with 2 small appliance branch circuits and a laundry circuit?

a. 10,500 watts
b. 6,000 watts
c. 5,625 watts
d. 3,675 watts

The sample test I am using says that the correct answer is c. I can come up with 6,600 VA but that is as far as I can get. This is how I am coming to that. I do my lighting load calculation 2000 x 3 = 6,000. I turn to Table 220.42 and see that it says From 3,001 to 120,000 use 35% Demand Factor. So I take 6000 x 35% which gives me 2,100. I then turn to section 220.52 sections A and B. That gives me 4,500. I add that to my previous 2,100. 4,500 + 2,100 = 6,600 VA.
What am I doing wrong. I am using NEC 2011. Thanks for all the help.

 

[topgone]

5625 is the neutral VA.
General lighting load = 2000 X 3 = 6000
2 circuits fr appliances = 1500 X 2 =3000
1 laundry circuit = 1500 X 1 =1500
Total = 6,000 + 3,000 + 1,500 = 10, 500
1st 3000 = 3000
35% of total = 7,500 X 0.35 = 2,625 VA

Grand total = 3,000 + 2,625 = 5, 625 VA
Your total load is:
1st 10,00 = 10,000VA
plus 40% of rest = 550 X 0.4 = 200VA
Total = 10,200 VA

 

[kefox81]

I appreciate that

I appreciate that

5625 is the neutral VA.
General lighting load = 2000 X 3 = 6000
2 circuits fr appliances = 1500 X 2 =3000
1 laundry circuit = 1500 X 1 =1500
Total = 6,000 + 3,000 + 1,500 = 10, 500
1st 3000 = 3000
35% of total = 7,500 X 0.35 = 2,625 VA

Grand total = 3,000 + 2,625 = 5, 625 VA
Your total load is:
1st 10,00 = 10,000VA
plus 40% of rest = 550 X 0.4 = 200VA
Total = 10,200 VA

Thanks for showing me how to do that. I don't understand what you mean by 1st 3000? Can you explain please?

 

[Danelectron]

Thanks for showing me how to do that. I don't understand what you mean by 1st 3000? Can you explain please?

This comes from table 220.42 in the line above the one you applied to your calculations. The first 3000VA @ 100% then 3001 to 120000 @ 35% then the remainder over 120000 @ 25%.

 

[JFletcher]

Welcome. edited my reply as I misread the question. topgone is correct.

 

[Danelectron]

This comes from table 220.42 in the line above the one you applied to your calculations. The first 3000VA @ 100% then 3001 to 120000 @ 35% then the remainder over 120000 @ 25%.

kefox81, I hope I didn't come across too blunt. Wasn't trying to be condescending, sometimes I don't word things so eloquently. I'm going over some of the examples in the NEC (Annex D) and backtracking where I miss something. It helps me to read explanations such as topgone provided. There are a lot of steps to these demand problems and it's easy to miss (or misplace) a piece of info.

 

[Dennis Alwon]

5625 is the neutral VA.
General lighting load = 2000 X 3 = 6000
2 circuits fr appliances = 1500 X 2 =3000
1 laundry circuit = 1500 X 1 =1500
Total = 6,000 + 3,000 + 1,500 = 10, 500
1st 3000 = 3000
35% of total = 7,500 X 0.35 = 2,625 VA

Grand total = 3,000 + 2,625 = 5, 625 VA
Your total load is:
1st 10,00 = 10,000VA
plus 40% of rest = 550 X 0.4 = 200VA
Total = 10,200 VA

The 40% for the first 10,000 is for optional calculation. C) is the correct answer for the general lighting load not the neutral load. Maybe I am reading your post incorrectly but it appears we disagree.

 

[kwired]

The 40% for the first 10,000 is for optional calculation. C) is the correct answer for the general lighting load not the neutral load. Maybe I am reading your post incorrectly but it appears we disagree.

I agree with you, he had me confused, the 5625 I agreed with, but then all of a sudden we were jumping to 10k figures.

If you want the minimum allowed you have to figure both methods and pick the smaller result.

 

[kefox81]

No worries.

No worries.

kefox81, I hope I didn't come across too blunt. Wasn't trying to be condescending, sometimes I don't word things so eloquently. I'm going over some of the examples in the NEC (Annex D) and backtracking where I miss something. It helps me to read explanations such as topgone provided. There are a lot of steps to these demand problems and it's easy to miss (or misplace) a piece of info.

No worries.