# residential load calc



## EJPHI (May 7, 2008)

I am calculating the service size for a new residence using the 2005 code.

General purpose receptacles are assumed to have a 180 VA load on them.

Laundry area branch circuits are assumed to have a 1500 VA load. This is reasonable given the amount of power a hand iron can consume.

Bathroom receptacles must have a 20A circuit but there is no mention of the assumed load.

180 Va doesn't seem right. My wife uses a hair dryer and warms up her styling wand at the same time. we're talkin' KW territory here. It seems proper to use something near the 1500 VA value used in the laundry area.

Maybe the statistical nature of what gets used when comes into play. I don't have 180 VA on my genreral receptacles all the time.


Looking forward to enlightenment.

EJPHI


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## Dennis Alwon (May 9, 2009)

The loads for the bathroom and other areas are figured in at the 3 watts per square foot for the residence. You do not need to worry about the bathroom recep. specifically.


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## MDShunk (Jan 7, 2007)

Unless your wife heats up all her bathroom hair appliances at the same time she's ironing clothes and cooking on all four burners, I don't think you have anything to worry about. The NEC prescribed calculation methods are very close to the worst case scenario. Just follow them and don't overthink this.

If a certain feature worries you (like, perhaps you think you need two circuits in the bathroom), feel free to install an extra circuit. That doesn't effect the load calc in the least, though.


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## EJPHI (May 7, 2008)

Thanks for the answers. I understand that the NEC calcualtion method give good real world results, but why did they single out laundry areas for special demand?

Trying hard not to over think this.

This project is interesting from many perspectives. The architect put chandeliers in out to wazoo and has lights all over the place.

I'm pegging a Title 24 chandelier at 300W.

I sure won't be using 3 VA/ft^2 on the lights!! 220.42 seems like the way top go.

These calculations remind me of tax time!!

EJPHI


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## Dennis Alwon (May 9, 2009)

EJPHI said:


> Thanks for the answers. I understand that the NEC calcualtion method give good real world results, but why did they single out laundry areas for special demand?
> 
> Trying hard not to over think this.
> 
> ...


300 watts is not so much for a chandelier. I probably would not worry about going more than 3 watts/sq.ft but you certainly can if you want.

The reason they included the laundry at 1500 watts is because they can safely guess what that load will be and it is required in every single family dwelling.

I have done many homes with 400 amp and a few with 600 amps and one with a 1200 amp service. 3 watts works just fine for calculation purposes and I bet that on a normal day that 1200 amp service won't even draw near 600 amps.


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## MDShunk (Jan 7, 2007)

Even if you use the alternate calculation methods, it would be very rare for that to throw you into the next service size.


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## EJPHI (May 7, 2008)

Thanks for the comments.

Just to close the loop; 3 VA/sq ft would give me 15 KVA for lighting on this 5000 square foot house.

Adding up everything on the prints gets me to 12.9 KVA. The alternative method in 220.42 gives 6.45 KVA. So another data point to support the idea of using 3 VA/sg ft.

The total load came out to 340A.

There is now talk of a 15-20 KVA back-up generator with an ATS and separate panel for critical loads. I think the circuits on that panel (in order of importance) will be:

1)HVAC
2)Refrigeration
3)Some cooking
4)Some lighting branch circuits
5)Some receptacle branch circuits
6)Wine cellar:thumbsup:

I'm sure this list will change after talking to the owner.

EJPHI


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## nitro71 (Sep 17, 2009)

Just go with what the correct load calc tells you for service size. Nobody turns every light on in the house at once and all the appliances on at the same time. If you list the square foot, heat load, ac load, whether it's a electric range and electric dryer and any other loads then post your calc up. I'll check it tommorow if you like or someone else will beat me to it.


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## Dennis Alwon (May 9, 2009)

Go to this web page and click on residential load calculation.


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## EJPHI (May 7, 2008)

Nitro,
Thanks for the advice. I think I have everything covered, at least any way I calculate it, 400A seems to be correct.

Dennis,
That is a very good site. Lots of good stuff. Thank you for your post.

EJPHI


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## Dennis Alwon (May 9, 2009)

EJPHI said:


> Nitro,
> Thanks for the advice. I think I have everything covered, at least any way I calculate it, 400A seems to be correct.
> 
> Dennis,
> ...


 You're welcome


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