Calculating the load for all electric 2400 sqft home w/

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aelectricalman

aelectricalman

Senior Member
Location
KY
With a 20KW Furnace in a home that is 2400Sqft (All electric) would you see a problem using a 200 Amp service. Should I use a 300 Amp Service.

I figured 20000/240 = 83 Amps for Furnace
= 50 Amps for the Range
Alone with just these two working simultaneously we are already at 133 Amp.

After figuring in the water heater and the Dishwasher working at the same time as the two mentioned earlier, we add roughly 25Amp. Now we are at around 158 Amps on a 200 Amp service. Is there ample space left to maintain basic functions of a homes electrical system and to keep the system from tripping. Does anyone know how to figure out a round about basic load for everyday usage on normal lighting and non- appliance plug circuits. Baically, I want to know what does it normally take to keep up all bedroom circuits, living room circuits, and basement and other 15 and 20 amp circuits. Thanks for any help
 
Re: Calculating the load for all electric 2400 sqft home w/

If this were my house I'd be ticked if you put in a 200A service. If they can afford to pay for electric heat they can pay for the service to feed it.
 
Re: Calculating the load for all electric 2400 sqft home w/

You are taking the wrong approach to the math. Don?t add up amps. Add up watts. You need to perform a service calculation per Article 220. That article includes a table for general lighting loads, tables for ranges and dryers, specific rules for heating systems, lists of items you have to install even if the owner doesn?t want them, lists of items you have to count even if they are not installed, and demand factors that can be used to reduce the overall calculated load. We do not get to make up our own concepts of what will, and what will not be running at the same time.
 
Re: Calculating the load for all electric 2400 sqft home w/

If it were my home, yes I would as well go with a 300 Amp, but with that not being the case I have already quoted the job for a 200 Amp serivce. Which is fine, I will only lose out for an extra 100 Amp addional panel plus the wire and extra fittings. I will probably lose $350, but if it can be avoided, I would like to take home that $350.00. Unfortunatly, we all know that there is a fine line for profit in residential anyhow. Thank you.
 
Re: Calculating the load for all electric 2400 sqft home w/

Thanks Charlie, I did use watts and just divided to find amps. But, I am glad you brought these articles to my attention. I should have realized it was not to my liberty to decide. Thats why we have NEC. Thank you.
 
Re: Calculating the load for all electric 2400 sqft home w/

Wait a minute, like charlie b says, get an Article 220 calculation done. You may find it beneficial to Do the calc in VA, not in amps, not in watts.

You will find that you certainly do not figure a full 50A for a range. Isn't the range branch ckt. going to be 50A at the most ?

You may very well find that 200A service entrance conductors are code legal for this house.
 
Re: Calculating the load for all electric 2400 sqft home w/

As Charlie mentions, take a look a Art 220 and calculate loads applying related demand factors for your final Service size. Secondly, I would look into using a heatpump instead of a brute kva heating furnace. Stage the furnace with heatstrips to compensate for the climate zone where the residence is situated.

With all that said, an AEK and heatpump (at least 14 Seer) for a 3000 sf house would still meet a comfortable 42 to 45 kva capacity 42,000/240V= 175 Amps for a 200 Amp panel.

If you are in the high country, I would recommend LP gas for cooking and H2O to cover occasional outages. If in the city, natural gas is practical for furnace and H2O heating minimum.

rbj, Seattle
 
Re: Calculating the load for all electric 2400 sqft home w/

rbj Heat pumps are ineffective in many areas.

That said electric heating is going to be costly. :eek:
 
Re: Calculating the load for all electric 2400 sqft home w/

I guess that I fail to understand why this is so difficult. No disrespect intended, but shouldn't all electrical contractors know how to do a basic whole house load calc. As an instructor I have noticed a common thread over the years. When asked why an electrician does something a certain way the reply is "that's the way we've always done it". I would strongly suggest that anyone that has learned electrical installation through OJT, take some courses on the NEC. And then get some continuing education to keep up with the changes
 
Re: Calculating the load for all electric 2400 sqft home w/

Originally posted by jkgipe80:
I guess that I fail to understand why this is so difficult. No disrespect intended, but shouldn't all electrical contractors know how to do a basic whole house load calc. As an instructor I have noticed a common thread over the years. When asked why an electrician does something a certain way the reply is "that's the way we've always done it". I would strongly suggest that anyone that has learned electrical installation through OJT, take some courses on the NEC. And then get some continuing education to keep up with the changes
Click to expand...
I agree with your entire post.

One problem is that there are many areas that have little or no licensing or C.E. requirements.

Roger

[ December 23, 2004, 08:19 AM: Message edited by: roger ]
 
Re: Calculating the load for all electric 2400 sqft home w/

Tx Bob, I agree with you 100%. I did put wiggle room in mentioning climate zone. I have done high-country installation air-air and they do bog down occasionally.
Going back to Art 220, there is still enough leeway for an electrical furnace to still come under the 200A panel capacity for a 2400sf home.

aelectricalman,
What's the climate like there anyway?
rbj, Seattle
 
Re: Calculating the load for all electric 2400 sqft home w/

Actually Keith, before I made the post, I did the load calculation for the home. The Load demand came out to be 47,857 VA. I did it using a spreadsheet I got from "SCHOOL". The reason I sent the email out for help is because it is 199Amps . +/- 3% that puts me very close to 200 Amps. Using the NEC specs for load also yielded about the same. About 196 Amps. I wrote because I wanted an opinion as to whether or not the load calculations are accurate enough to proceed with a 200 amp service. Oh, and by the way, I have passed the Masters and Contractors Exam for both Illinois and Kentucky. CE18822 and ME 18821. I'm pretty sure that most if not all states require statewide licensing now.
 
Re: Calculating the load for all electric 2400 sqft home w/

Aelectricalman; Illinois, Indiana, Iowa, Kansas, Louisiana, Missouri, New York, and Pennsyvania are states with no statewide licensing according to this page.

There are others with licensing but no C.E. and some of the licensing requirements are quite lax in comparison to other states.

Why not post all the numbers in your calculation if you are asking for a true evaluation of your conclusion.

Roger
 
Re: Calculating the load for all electric 2400 sqft home w/

Originally posted by kiloamp7: You may find it beneficial to Do the calc in VA, not in amps, not in watts.
Click to expand...
True, but it is a distinction without a difference. There is not one item in the Article 220 calculation process (not even motors) for which power factor comes into the picture. ?Real power,? as measured in ?watts,? and ?apparent power,? as measured in ?volt-amperes,? will have the same numerical value.

There is an FPN under 220.3(A) that gives the designer the hint that power factor, and perhaps other considerations, may make it appropriate to allow for more load. But the motor load is determined by taking the amps from the tables, and multiplying by volts, without separately accounting from either power factor or efficiency. We are left to presume that those two factors are built into the amp values in the motor tables.

All that having been said, it is indeed customary to express the calculated power in terms of VA. That is what I should have said in my earlier post. So thank you, kiloamp7 for pointing this out to me.
 
Re: Calculating the load for all electric 2400 sqft home w/

Im sorry, I should have been more precise in my wording. I am licensed in KY, but do work in both Illinois and Kentucky. After all, I did only post the KY CE and ME numbers. My bad.
Anyhow to answer your question, here are my numbers. Please evaluate and give your conclusion. Thank you forum.

General Lighting load = 2100 X 3 = 6300VA
2 Kitchen Circuits 2@1500 VA = 3000VA
1 Laundry Circuit @1200 VA = 1500VA

10,800 VA
with 3000@ 100% 3000VA
and 7800@ 35% 2730VA So general lighting load is 5730VA
Heat is 20000VA
The AC is 4ton @125% is 8900VA which is less than furnace so we use the furnaces VA

Now we have a lighting load at 5730VA, Furnace at 20000VA which gives us 25730VA. Now we add for:
Water Heater 4,500VA
Refrigerator 1,400VA
Dishwasher 1,030VA
Microwave 1,630VA
Electric Range 8,000VA
Dryer 5,000VA

Add it all up and you get roughly 47200VA

That is about 197 A Assuming all is accounted for in the home, is safe to staying with a 200 Amp service. Does the NEC set these standards as a safe threshold to stay under. Is there a margin of error built into there equations and numbers on the plus side of 196A. Do I have any cushion. Or should I just be safe and go with 300Amp. (300 is next size available to me). Thank you ole experienced one for thy help :confused: !!!
 
Re: Calculating the load for all electric 2400 sqft home w/

note I keep my calculations in VA not watts. I did not include power factor.
 
Re: Calculating the load for all electric 2400 sqft home w/

IMO 300A is a waste of material & labor. Much research has gone in to the development of Article 220 service/feeder calculations for single-family dwellings.

If your number is 197A, then a 200A service is fine.
Just the fact that 310.15(B)(6) allows "increased ampacities" for this 120/240V. 1-PH 3-W dwelling service, tells you that there are safety factors built in.

Also, remember 220.17 for (4) or more fastened-in place appliances.
It can frequently be used to help lower the amp number.
Many AHJ's may say that the refrigerator load is considered as part of the (2) kitchen ckts. that you have included.

And then there is the optional method, which will probably lower the number even more.

[ December 25, 2004, 08:36 PM: Message edited by: kiloamp7 ]
 
Re: Calculating the load for all electric 2400 sqft home w/

Originally posted by kiloamp7:


Many AHJ's may say that the refrigerator load is considered as part of the (2) kitchen ckts. that you have included.
Click to expand...
Actually, the AHJ has no choice in the matter. It's right there in 220.16 (A) exception. :D
 
Re: Calculating the load for all electric 2400 sqft home w/

220.30(optional calulation)dwelling unit
2100x3=6300
3000
1500
5000 dry
8000 range
4500 w.heater
1287.5@1.25%D.washer motor
1630 microwave
____
31,217.5
-10,000
------
21,217.5
x O.40
_________
8487
+10,000
_______
18487va
+ 20,000 heat@100%
___________
38,487va
divided by 240=160.36 amperes=160
on information as posted.
 
Re: Calculating the load for all electric 2400 sqft home w/

So, the load demand for appliance circuits already figures in the refrigerator in the 3000VA countertop circuits. Is this the case? Is the refrigerator not to be figured seperately unless receptacle is ran in dedicated circuit other than 2 countertop circuits?
 
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