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Mega Houses #46149 12/14/04 07:59 AM
Joined: Jul 2004
Posts: 49
GamecockEE Offline OP
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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Re: Mega Houses #46150 12/14/04 09:24 AM
Joined: Nov 2004
Posts: 80
Bert66 Offline
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!!!

Re: Mega Houses #46151 12/14/04 11:08 AM
Joined: Aug 2001
Posts: 7,520
pauluk Offline
Anything over about 3000 sq. ft. would be classed as a mansion over here!

Re: Mega Houses #46152 12/14/04 12:43 PM
Joined: Jul 2004
Posts: 49
GamecockEE Offline OP
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.

Re: Mega Houses #46153 12/14/04 01:07 PM
Joined: Jul 2004
Posts: 272
A-Line Offline
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.

Re: Mega Houses #46154 12/14/04 04:04 PM
Joined: Jul 2004
Posts: 49
GamecockEE Offline OP
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.

Re: Mega Houses #46155 12/14/04 07:29 PM
Joined: Jun 2004
Posts: 613
shortcircuit Offline
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.


Re: Mega Houses #46156 12/14/04 09:06 PM
Joined: Dec 2004
Posts: 27
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).]

Re: Mega Houses #46157 12/14/04 10:39 PM
Joined: Nov 2003
Posts: 127
Sir Arcsalot Offline

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.
Re: Mega Houses #46158 12/14/04 11:34 PM
Joined: Apr 2002
Posts: 2,527
Bjarney Offline
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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