Single family dwelling service load calculation help! - Electrician Talk - Professional Electrical Contractors Forum
 Electrician Talk - Professional Electrical Contractors Forum Single family dwelling service load calculation help!
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 10-04-2010, 05:23 PM #2 Moderator     Join Date: May 2009 Location: Chapel Hill, NC Posts: 19,426 Rewards Points: 576 From T. 220.42 we see that the first 3000 va is at 100% and the up 120,000 at 35%. Let's say we have a calculated lighting load demand factor of 11,500 va. This means the first 3000 are at 100% which equals 3000va Now the rest of the load is at 35%. So we have 11,500- 3000= rest of the load = 8,500. 8500 X 35%= 2975va. So now we have a total of 3000va+2975va= 5975va. Now you calculate the range, dryer, etc. Look at Annex D in the back of the NEC for a good example-- example D(1)
 The Following User Says Thank You to Dennis Alwon For This Useful Post: dadtodc (10-05-2010)
 10-04-2010, 07:54 PM #3 Member   Join Date: Oct 2010 Location: Greenville SC Posts: 31 Rewards Points: 25 ahhh Man I really sat and stared at annex "D" for ever. This is the example from annex D only square feet changed. I could not get this at all. I got it now. Thanks a ton for the information I really do appreciate it. I am taking the trst on Saturday, and I am just not getting the small stuff!
 10-04-2010, 08:03 PM #4 Member   Join Date: Oct 2010 Location: Greenville SC Posts: 31 Rewards Points: 25 One more thing, why does it only add up the small appliance and the kva per square foot to get the 9000. is it because the laundry circuit isnt considered because it isnt part of the lighting load. or am I way off?
10-05-2010, 10:55 AM   #5
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Quote:
 Originally Posted by dadtodc One more thing, why does it only add up the small appliance and the kva per square foot to get the 9000. is it because the laundry circuit isnt considered because it isnt part of the lighting load. or am I way off?
The laundry circuit can be included in the lighting loads and be subject to the demand factors of Table 220.42. Take a look at the last sentence of 220.52(B).

Chris

10-05-2010, 12:18 PM   #6
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 Originally Posted by raider1 The laundry circuit can be included in the lighting loads and be subject to the demand factors of Table 220.42. Take a look at the last sentence of 220.52(B). Chris
Ok, I read the sentence and I see that it can be used. I read that before and that is why I asked. So if that is the case then in myexample why is the laundry load not used in the calculation? Ihave 6000kva, for the sqft, and 3000kva for the 2 1500kva circuts. That is where the 9000 comes from right. I alsohowever have a single 1500kva from laundry that isnt used. That I think is what keeps throwing me off.

10-05-2010, 12:39 PM   #7
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Quote:
 Originally Posted by dadtodc Ok, I read the sentence and I see that it can be used. I read that before and that is why I asked. So if that is the case then in myexample why is the laundry load not used in the calculation? Ihave 6000kva, for the sqft, and 3000kva for the 2 1500kva circuts. That is where the 9000 comes from right. I alsohowever have a single 1500kva from laundry that isnt used. That I think is what keeps throwing me off.
The problem is that after you take to 3000 VA at 100% you used 9000 instead of 10,500 to subtract the 3000 VA.

Chris

 The Following User Says Thank You to raider1 For This Useful Post: dadtodc (10-05-2010)
10-05-2010, 08:18 PM   #8
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 Originally Posted by raider1 The problem is that after you take to 3000 VA at 100% you used 9000 instead of 10,500 to subtract the 3000 VA. Chris
Ok I am with you now. The reason I was doing that is because the example I gave you was from a prep CD I bought. It differed from the annex "D", but made absolutly no sense to ma at all. Thanks so much for clearing all of this up!

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