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Residential load calculation #87153 01/26/04 09:59 AM
Joined: Jan 2004
Posts: 615
Jps1006 Offline OP
Hi guys. I’m new here, but I’ve been reading some of the posts for the past few days, and you guys have been cracking me up.

I’ve got questions about residential load calculations. I’m doing one for an existing house, and as I walked the place I realized I wasn’t 100% sure of how to treat some of the loads.

Do I figure garage door openers as fixed appliances? (I couldn’t find any examples in the code or online that mention this)

If I exempt the garage sq. footage how are the lights and coach lights accounted for?

How would you treat landscape lighting?

Sump pump & ejector pits fixed appliance?

What about refrigerators and freezer? I was under the impression refrigerator loads were figured in under the small appliance branch circuit.

Refrigerator and freezer in garage aren’t technically “fixed.”

We can start with these, I look forward to the discussion.


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Re: Residential load calculation #87154 01/28/04 07:43 AM
Joined: Jan 2004
Posts: 615
Jps1006 Offline OP
I’ve got this house figured up, but I’m still looking for some input.(anyone?)

If I figure it up standard: 186 amps
If I figure it up optional: 166 amps

A little bit of a variation. Is there a better way to figure this than what the NEC has laid out in the book? Obviously a lot of room is there for someone to use some discretion.

If I plug some numbers in a little different I get as much as 193 amps. Now it is my personal feeling that these bigger custom homes have way more ampacity than will ever get used. I’ve done them with 600 amp services before. I would bet those service entrance conductors never see a day over 150 amps.

So I lean heavily toward wanting to tell this guy, no problem, you still have room for another oven if you want. But I’d feel better crunching the numbers using a different engineering method, if one exists. Any suggestions?

Re: Residential load calculation #87155 01/28/04 10:46 AM
Joined: Feb 2002
Posts: 375
George Offline
Like you say:

"Obviously a lot of room is there for someone to use some discretion."

From your calculations it seems that 200amp is enough.

I don't know the price difference between 200amp and the next step up so I cannot comment on which you should do. For $500 an extra 200amp ending in a disconnect and no panel might be worthwhile.

Re: Residential load calculation #87156 01/28/04 01:54 PM
Joined: Dec 2003
Posts: 751
earlydean Offline
Computing by code is the minimal standard. Go for the 400 Amp. It is my experience that owners of these custom homes count the size of the service as a matter of pride. "My house has a bigger service than your house".
You want the job? Tell the owner according to your calculations, he will need to upgrade to 400 Amps before the decade is out, so you suggest he has you install 600 Amps, just to be safe. (with an automatic back-up emergency generator, too)


Re: Residential load calculation #87157 01/28/04 07:46 PM
Joined: Oct 2000
Posts: 5,389
sparky Offline
heh~i work for those sorts alot here Earl, and yes that tactic works well, and beats splittin' hairs....

there were some on-line residential demand load calc's floating about here at one time...


Re: Residential load calculation #87158 01/29/04 10:27 AM
Joined: Jan 2004
Posts: 615
Jps1006 Offline OP
Thanks for the input.

This is an existing house (20 years old). The problem is that the difference is quite large between leaving it as is, and a new 400 amp service. The city will make us put the new meter on the side of the house which makes it tricky getting through the finished basement ceiling to refeed the existing panel and finding an appropriate spot for the new panel. I’m going to throw out $5000 as a rough idea (maybe $6000).

I admire your zeal for salesmanship. Yes, if it were new construction I’d push toward the 400 for obvious reasons, mainly being that for the extra cost now verses doing it later, you’d be silly to think there was any good reason not to go 400.

I don’t care either way about getting the job due to the PITA factor. But if I do sell him a 400 amp upgrade, I would rather that while I grunt, sweat, and scratch my head, it would help to feel like I’m doing this because it really needs it.

I just don’t feel convinced that the NEC’s load calc. method is appropriate for these bigger homes. And maybe that’s based on what we see the POCO doing (I know I’ve that discussion around here before) – 42,000 VA worth of calculated load fed off a 25KVA transformer with 5 other homes.

I looked back to July posts and didn’t see anything. It’s too easy to get distracted around here. I’ve only been here a few days and I’ve spent hours and hours looking at what people are saying. Should I expect this number to go up or down. I hope down once I get up to speed.

Re: Residential load calculation #87159 01/29/04 06:08 PM
Joined: Oct 2000
Posts: 5,389
sparky Offline
Check this one out John...

Demand Load calc


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