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Old 08-31-2009, 09:33 PM   #16
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Service Load Calcs and Install


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Originally Posted by sstinman View Post
Assuming I did the calculations correctly then I'm in for a fight with the builder.
For "material breach of contract." There is also an "implied warranty of merchantability".
Monitor the current draw with a clamp-on ammeter while you turn on each 240v device and then a reasonable amount of 120v stuff.
I'd contact your state's attorney right after the main breaker trips.


Last edited by Yoyizit; 08-31-2009 at 09:36 PM.
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Old 08-31-2009, 09:36 PM   #17
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Service Load Calcs and Install


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Originally Posted by sstinman View Post
Guys I have used the residential calc and get a 260amp service load.

Please look at the PDF file found under the picture.

[IMG]file:///C:/DOCUME%7E1/SPASEN%7E1/LOCALS%7E1/Temp/moz-screenshot.png[/IMG]
I just used a different load calculation spreadsheet, using the values you stated in your post (and fudging some of the info that I didn't have exact values on) I come up with 175 amps. This is down and dirty and definitely not accurate as there are a lot of specifics that I didn't know as far as appliance ratings and such. Looking at your spreadsheet I see a few errors that are throwing your values off.

First, your A/C load in reality is approx. half the value you put into the spread sheet - you gave the values at 5 ton @ 19,100va and 2 ton @ 8,800va. These values should be 8,900va and 4,400va respectively.

Next, you put your electric dryer in as 7,200va, I don't know the nameplate rating on your dryer, but that may be a little high. I figured it at 5,000va.

Also, your cooking appliance demand load you have input as 14,000va but I have figured it at 10,920va.

These values as well as others would be the difference between your calculation and mine. As you have stated you don't really know if you're inputting the correct values into the spreadsheet, and I can not say for sure if I am either as I do not have all the information necessary to do so. The best advice I can give you is if you have concerns have a licensed electrician come over and do an accurate load calculation. However, as I and others have stated, I believe that your current service is probably sufficient.
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Old 08-31-2009, 09:38 PM   #18
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Service Load Calcs and Install


http://www.wholesalesolar.com/pdf.fo...ower-table.pdf

Also check if the breaker holds after a ~one hour power failure, in which case all the compressors would come on at once.

BTW, you can use your wattmeter as an ammeter.
http://en.wikipedia.org/wiki/Electricity_meter
and look under
Reading electromechanical meters
This pic shows the 7.2 factor
http://en.wikipedia.org/wiki/File:Electrical_meter.jpg

Last edited by Yoyizit; 08-31-2009 at 09:45 PM.
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Old 08-31-2009, 09:46 PM   #19
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Service Load Calcs and Install


My stove is rated at 14,100
He has a double oven + a cooktop, I only have a 1 oven range
My dryer is rated at 5600
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Old 08-31-2009, 09:50 PM   #20
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Quote:
Originally Posted by Yoyizit View Post
http://www.wholesalesolar.com/pdf.fo...ower-table.pdf

Also check if the breaker holds after a ~one hour power failure, in which case all the compressors would come on at once.

BTW, you can use your wattmeter as an ammeter.
No offense, that chart is great for a ballpark guesstimate, but is completely useless in terms of doing a load calculation.

The OP's problem pretty much boils down to the fact that in order to do a true and accurate load calculation you need the actual nameplate values for appliances, without that (or at least being close) you might as well be pulling numbers out of a hat.

Before getting into a pissing contest with the electrician or GC, you need to have an accurate load calculation done by a licensed electrician.

Did I mention, hire a professional to do an accurate load calculation.

Or you could hire a professional, licensed electrician, and have him do an accurate load calculation.
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Old 08-31-2009, 09:59 PM   #21
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Quote:
Originally Posted by Scuba_Dave View Post
My stove is rated at 14,100
He has a double oven + a cooktop, I only have a 1 oven range
My dryer is rated at 5600
Exactly my point. There is a thing called demand factor, which essentially means that your stove is rated at 14,100va if every heating element were on full at the same time. This is highly unlikely, so for the purposes of a load calculation we can take that value at a demand factor. The demand for a 14,100va range would be 8,800va.

Demand values are also taken for other appliances, general lighting loads, and etc. throughout the entire load calculation process (not everything thing in the house will be on at the same time). This is the reason why you can not just take nameplate values or breaker ratings and add them up to come up with a total service amperage. This is also the reason why the OP's calculation came out as high as it did, and the reason he needs to hire someone who knows what they are doing and can take the correct values to do an accurate load calculation.
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Old 08-31-2009, 10:09 PM   #22
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Originally Posted by EBFD6 View Post
Exactly my point. There is a thing called demand factor, which essentially means that your stove is rated at 14,100va if every heating element were on full at the same time. This is highly unlikely, so for the purposes of a load calculation we can take that value at a demand factor. The demand for a 14,100va range would be 8,800va.

Demand values are also taken for other appliances, general lighting loads, and etc. throughout the entire load calculation process (not everything thing in the house will be on at the same time). This is the reason why you can not just take nameplate values or breaker ratings and add them up to come up with a total service amperage. This is also the reason why the OP's calculation came out as high as it did, and the reason he needs to hire someone who knows what they are doing and can take the correct values to do an accurate load calculation.
Yup, the calculator I used you enter the full values, then it calcs out the demand automatically.
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Old 08-31-2009, 10:17 PM   #23
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I went to double check a couple of details:

Cooktop nameplate load is 6700 watts
Double Oven nameplate lead is 8100 watts
Dryer (11 amps max is all I could find x 120 volts) is 1320 volt*amps

The A/C condenser unit say 37.4amps MIN 60amps MAX (at 240v)
the blower motor is 3/4Hp (560 watts by conversion) this is where I'm fuzzy the spreadsheet I was using had built in values given the tonnage of the unit.

On last detail I looked at is the wires coming into the house, are 4/0 aluminum. I saw somewhere that these can take a much higher load maybe 400amps each leg????? Can anyone confirm?
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Old 09-01-2009, 09:30 AM   #24
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4/0 AL used in a residential service is good for 200 amps.
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Old 09-01-2009, 10:13 AM   #25
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Re: demand factor, assume there is a party going on and all the 240v loads are on, full.
Using nameplate data, how close does this 240v current draw come to 200A?

BTW, small motors are very inefficient.
http://books.google.com/books?id=DDs...%20NEC&f=false
See table 430.248.

Last edited by Yoyizit; 09-01-2009 at 10:15 AM.
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Old 09-01-2009, 06:16 PM   #26
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Service Load Calcs and Install


Quote:
Originally Posted by sstinman View Post
But what about the builder, electrical contractor, the city inspector, the home inspector who all promised me the electrical was installed correctly for the load and meets minimum code requirements as outlined in NEC article 220? I haven't installed any extra appliance or equipment (other than the home office equipment). The builder installed all the appliances.
In my opinion, you're wasting your time. As Magnettica and other posters pointed out to you that your calculations are wrong. First and foremost, without having the nameplate ratings in Amperes, or FLA in the case of large motors & compressors you're just doing guesswork. Besides, to do a proper service/demand calculation, you have to take the square footage of the house in consideration. Also, some segments of the load are calculated @ 80% of their face value. As I said in a previous post, that just guessing by the amount of appliances you have, you're probably pulling a load of 160 Amps when all the appliances are used in a regular manner. (Eliminate Confusion through Education!!! Don't Drink and Drive!!!
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Old 09-01-2009, 06:30 PM   #27
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Based on his PDF calculations I assumed his sq footage at 4,045 sq ft looking at the lighting load
That's a fairly big house
That calc sheet is different from the Excel spreadsheet I use
I enter all actual loads, 1st 10,000w calc'd at 100%, then 40% of the rest?
I'm not sure how it actually works
But I've checked it against several online calcs & it's always around the same figure

If you are concerned the House is under powered then have an electrican check out everything & run a true load calc
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Old 09-01-2009, 08:22 PM   #28
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I don't think you will have a problem. Up until about 9 months ago I had a 150amp service, I now have a 200 amp service. I am running a 4ton a/c, a 3ton a/c, a boiler, a furnace, 2 fridges, 2 dryers, an elect range, a bunch of tv's and computers, water pump, sump pump (in the wet seasons), and a lot of lights. My house is approx 3300sf now, we added 1500sf on in 2005. The whole time it was a 150 amp service we NEVER tripped the main breaker with all this stuff.
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Old 09-01-2009, 09:07 PM   #29
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I've found the name plate loads for every appliance except for the A/C units. I di find the spec sheet and can see the MCA is 37.5 for the 5 ton unit and 18.4 for the 2.5ton unit.

To get the kVA do I take the (MCA + Fan Motor) * 240v
MCA is minimum circuit amps

(37.5 + 1.4) * 240 = 9.4kVA ???? But should I add the blower motor for the inside unit (12amps * 120 = 1.44 kVA) thus giving a total of about 10.8kVA ??

Cooktop 6.7 kVA at 240v
Double Oven 8.1 kVA at 240v
Dryer 7.2 kVA at 240v

Microwave 1.8 kVA
Dishwasher 1.2 kVA
Frig 1.4 kVA
Outdoor lighting 1.0 kVA
Disposal 828 kVA

3 GFI circuits (small appliance) = 4.5 kVA
1 laundry circuit = 1.5kVA

4045 sqft of house at 3VA per sqft is 12.1 kVA

Total (straight kVA) is 62.4 kVA

Applying a 40% demand after the first 10kVA is 31kVA (130 amp service)

Using Mike Holt's Calculator I get 52kVA (217amp service)
SEE the ATTACHED PDF file for details.

Using some of the on-line calcs at nojolt and others I get 235amps service

But I only have 48kVA worth of service coming to the house. So I'm going to pursue this further with a pro and the home inspector.
Attached Files
File Type: pdf NEC Article 220 Minimum Service-b.pdf (19.0 KB, 636 views)
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Old 09-01-2009, 09:10 PM   #30
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In my stupd opinion, I'd be impressed for a family to trip a 100 amp breaker. just my stupid opinion of course.

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