# Electrical Dwelling design

Discussion in 'General Electronics Chat' started by h.immo, Sep 1, 2013.

1. ### h.immo Thread Starter New Member

Apr 17, 2012
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0
Hi there
I hope this is the right place to post it ( if not I'm very sorry)

I'm facing a problem with the calculations of an multifamily dwelling building.
In the article 220 of the NEC it is written that I have to use a demand factor of 23% (if I have more then 62 dwelling).
But on the other hand I have to use a demand factor of 100% for mechanical loads like A/C, and 40% for lighting.

What do I have to do? calculate the power for each dwelling->multiply it by 100% for mechanical load+ 40% for the rest, then add them all together and then multiply by 23%.

I hope I made my problem clear.
Thank you for your time and help
Regards
H.immo

Last edited: Sep 1, 2013
2. ### Wendy Moderator

Mar 24, 2008
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This forum is good. I suspect another moderator has been here before I. If you have problems with a thread that needs moved just use the alert system ("")

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3. ### PackratKing Well-Known Member

Jul 13, 2008
843
219

Any attempt to shortcut it will not enamour your project to electrical inspectors...

Tear-out and re-do gets enormously expensive...

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4. ### GetDeviceInfo AAC Fanatic!

Jun 7, 2009
1,619
239
I'm not the one to help you as I abide by the CEC, but here's some things to look for;

Your basic demand load may require a first group of units at 100%, a second group at something less, and the balance at something even less. Electric ranges are added in similar fashion. A/C and heat are added at 100%, unless interlocked, then the higher load. Other loads are added at some percent. Common areas and parking are then added at some declining contribution.

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5. ### #12 Expert

Nov 30, 2010
18,076
9,678
Phone the inspectors for advice. If that fails, pay a real electrician to do the math. A couple of hundred dollars is cheap for the insurance it is going to buy you.

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6. ### h.immo Thread Starter New Member

Apr 17, 2012
10
0
sry didnt quit get what u meant ^^" ( what do you mean with "yes" )

The problem is that I was taught different than the NEC standarts ( or I dont get them right :/ )

thank you all for your help

7. ### PackratKing Well-Known Member

Jul 13, 2008
843
219

So yes, you must add all your demand together, and inlcude a small percentage for a " fudge factor "

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8. ### h.immo Thread Starter New Member

Apr 17, 2012
10
0
ok that was very helpful, thank you very much for your help