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#46149 - 12/14/04 04:59 AM Mega Houses
GamecockEE Offline

Registered: 07/28/04
Posts: 49
Loc: Georgetown, SC 29440
For discussion, in our area, we are starting to see more of these super large residences, >10,000 square feet built largely for entertaining. Asking the experience base that is out there, does the NEC demand factors for general lighting, & small appliance (as applied for dwelling units)seem to work? Or are designers treating them as commercial buildings?

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#46150 - 12/14/04 06:24 AM Re: Mega Houses
Bert66 Offline

Registered: 11/01/04
Posts: 78
Loc: Belle Chasse, La. USA
I have not done any this large, my largest to date has been 7000 sq. ft. But just make sure your calculations are correct. Nothing like putting power on and seeing the lights dip every time the dishwasher cycles. You can choose to go with the optional calculations here. Look at artical 220 in the NEC, it should be alot of help to you.

Best of luck to you!!!

#46151 - 12/14/04 08:08 AM Re: Mega Houses
pauluk Offline

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
Anything over about 3000 sq. ft. would be classed as a mansion over here!

#46152 - 12/14/04 09:43 AM Re: Mega Houses
GamecockEE Offline

Registered: 07/28/04
Posts: 49
Loc: Georgetown, SC 29440
I have seen the plans for some as big as 15,000 sq ft. Talking about the lights dimming, I think the biggest issue there is going to be how much transformer the utility is going to use to serve the load and the largest motor that has to be started across the line. You have to have some KVA to accomodate the voltage drop. The utility wants to put in the smallest possible unit to minimize transformer losses.

#46153 - 12/14/04 10:07 AM Re: Mega Houses
A-Line Offline

Registered: 07/23/04
Posts: 264
Loc: Utah, USA
I believe in my area the problem with lights dimming when large loads such as A/C kick on are coming from the Utility side. No matter how large the service is you would still have the problem.
I had a customer who had a 125 amp service. All appliances were gas except for the A/C Unit. His lights would dim when it started.
He insisted that he needed at least a 400 amp service to solve the problem. The house was less than 3,000 sq. ft. I did a load calculation and found that the 125 amp. service was large enough. I convinced him that a 200 amp service would be plenty big enough and he went with the 200 amp service.
I explained to him that his service size was not causing the lights to dim when his A/C kicked on. It was the utilities supply that was the problem.

#46154 - 12/14/04 01:04 PM Re: Mega Houses
GamecockEE Offline

Registered: 07/28/04
Posts: 49
Loc: Georgetown, SC 29440
A-line, I bet if you go and look there is probably a small xfmr serving the load. A motor starting across the line will draw 6 or more times its full load in the first 10 cycles or so. The voltage drop across that transformer will be the start-up current times the impedance, so there can exist a noticeable flicker, because the new voltage is supply voltage - the xfmr voltage drop. Does'nt really mean anythings wrong but objectionable to a point is in the eyes of the beholder.
The problem is that some of these clients in these upscale homes think that any flicker is not normal.

#46155 - 12/14/04 04:29 PM Re: Mega Houses
shortcircuit Offline

Registered: 06/27/04
Posts: 608
Loc: massachusetts
GamecockEE...what do you mean when you say the Utility Co wants to put the smallest possible unit to minimize transformer losses?

You probably will need a 600 amp service and a 75kva transformer at the pole to take the load of 10000sq feet.


#46156 - 12/14/04 06:06 PM Re: Mega Houses

Registered: 12/13/04
Posts: 28
Loc: WA
Thats funny, because I usually work on houses 10,000-30,000 sq feet that take years to do start to finish, I would love to do the "small' ones once in a while for a change of pace.

[This message has been edited by BEAMEUP (edited 12-14-2004).]

#46157 - 12/14/04 07:39 PM Re: Mega Houses
Sir Arcsalot Offline

Registered: 11/17/03
Posts: 117
Loc: Lynden, Washington

10,000 to 30,000 square feet? WOW!!! Where at? Redmond, WA (Bill(Gates)ville)?? Man, oh, man, houses like that must have their own separate area codes!!

Edited for el typo.

[This message has been edited by Sir Arcsalot (edited 12-14-2004).]
No wire bias here- I'm standing on neutral ground.

#46158 - 12/14/04 08:34 PM Re: Mega Houses
Bjarney Offline

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
One workaround for undersized transformers would be installing primary metering {at the street distribution voltage) and then feed whatever sized transformers you want. At >10∙ft², it might be similar to a school, hostspal or office.

And, you could have one or more 480V transformers for mechanical equipment, and one or two at 208V for lighting and convenience outlets. {In this area, you also get a 2½% discount for buying power at distribution voltage.}

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