Dwelling load calc., adding AC

[chris kennedy]

This is not my area of expertise, but I'm doing a favor for very good friends that recently purchased a home and are adding central AC. I'm submitting a permit application and want to include a load calc with it. Here is the calc I did off the top off my head. When I checked it today I noticed 220.83(B) which I have some questions about that will follow.

Please check this:

1200ft? @ 3VA = 3600
2 Sm. App @ 1500 = 3000
Laundry = 1500
Range = 8000
WH= 3500
Dryer= 3000

Total = 22,600

10,000@ 100% = 10,000
12,600@ 40%= 5,040

Total = 15,040

New 7.5kw heat = 7.500

Total = 22,540

22,540?240= 94A


Existing service is 100A, did I miss anything?

As always, thanks.

 

[augie47]

per 220.54 dryer should be figured at 5000 va.
In this area water heaters are normally 4500, is 3500 factual ?
refrigerator, diswasher, garbage disposal... ?? any other motors ?

 

[jwjrw]

per 220.54 dryer should be figured at 5000 va.
In this area water heaters are normally 4500, is 3500 factual ?
refrigerator, diswasher, garbage disposal... ?? any other motors ?

I agree about the dryer and waterheater.

 

[raider1]

Gus, using the optional calculations in Part IV you don't need to use the 5000 VA load specified in Part III you would use the actual nameplate rating of the dryer as well as the water heater.

Chris

 

[jwjrw]

Gus, using the optional calculations in Part IV you don't need to use the 5000 VA load specified in Part III you would use the actual nameplate rating of the dryer as well as the water heater.

Chris

I thought I read you use whichever is larger not actual nameplate.

 

[raider1]

I thought I read you use whichever is larger not actual nameplate.

That is in the standard method specified in Part III specifically 220.54.

But the original poster appears to be using the optional calculation in accordance with Part IV of Article 220.

Take a look at 220.82(A)

It shall be permissible to calculate the feeder and service loads in accordance with this section instead of the method specified in Part III of this article.

220.82(B)(3) says to use the nameplate rating of the dryer as well as the nameplate rating of the water heater.

Chris

 

[chris kennedy]

per 220.54 dryer should be figured at 5000 va.
In this area water heaters are normally 4500, is 3500 factual ?
refrigerator, diswasher, garbage disposal... ?? any other motors ?

No dishwasher, disposal or other motors. Where in 220 is refrigerator listed?

 

[jwjrw]

That is in the standard method specified in Part III specifically 220.54.

But the original poster appears to be using the optional calculation in accordance with Part IV of Article 220.

Take a look at 220.82(A)



220.82(B)(3) says to use the nameplate rating of the dryer as well as the nameplate rating of the water heater.

Chris

I see once again thanks raider

 

[augie47]

Using the optional method on the residential load calculator on MikeHolt.com , I get 85 amps.

 

[ceb58]

In the MH calculator the 7.5 kw heat it comes up with 8.3 kw to include the blower.

 

[chris kennedy]

Using the optional method on the residential load calculator on MikeHolt.com , I get 85 amps.

I love it. I'll give that a look. Thanks all.

Next question. If I wanted to use 220.83(B) the list shows 100% of AC equipment and 100% of central electric space heating. This seems to contradict 220.60.

 

[1793]

With the information provided by OP, in the calculator I used it shows 94 actual amps. I did use 4500 for WH & 5000 for Dryer.

 

[augie47]

I love it. Three experienced contractors/inspectors and we come up with different answers.
Thankfully I'm through taking test in my life.

 

[LarryFine]

Three experienced contractors/inspectors and we come up with different answers.

Well, they all agree that 100a is sufficient, don't they?

 

[augie47]

all that matters....:grin:
every time I have concern, I use the optional method.... it's amazing what a 200 amp service can hanlde using that method.

 

[jumper]

Where in 220 is refrigerator listed?

It is not directly. 220.52 exception leads you to 210.52(B)(1) exception (2) which says fridge can be on SABC or a separate circuit of 1500 amps or greater.

If I wanted to use 220.83(B) the list shows 100% of AC equipment and 100% of central electric space heating. This seems to contradict 220.60.

It is the larger of the two, look at the sentence before the table.

 

[chris kennedy]

It is not directly. 220.52 exception leads you to 210.52(B)(1) exception (2) which says fridge can be on SABC or a separate circuit of 1500 amps or greater.

Perfect, thanks.

It is the larger of the two, look at the sentence before the table.

I'm pleased to see that since I have 2 signed and notarized copies of the following being picked up tonight. Does this look OK?

Load calc for addition of new central AC to existing 100A
service. As per 220.83(B).

1200ft? @3VA = .......... 3,600
2 Sm. App. @1500VA = 3,000
Laundry = ................... 1,500
Range = .....................10,400
WH = .......................... 4,500
Dryer = ........................5,000
New heat = ................. 7,500
Total = .......................35,500 VA

8,000 @ 100% = ..........8,000
27,500 @ 40% = ........11,000

TOTAL = .....................19,000

19,000 ? 240 = 79 Amps

 

[jumper]

Perfect, thanks.




I'm pleased to see that since I have 2 signed and notarized copies of the following being picked up tonight. Does this look OK?

Load calc for addition of new central AC to existing 100A
service. As per 220.83(B).

1200ft? @3VA = .......... 3,600
2 Sm. App. @1500VA = 3,000
Laundry = ................... 1,500
Range = .....................10,400
WH = .......................... 4,500
Dryer = ........................5,000
New heat = ................. 7,500
Total = .......................35,500 VA

8,000 @ 100% = ..........8,000
27,500 @ 40% = ........11,000

TOTAL = .....................19,000

19,000 ? 240 = 79 Amps

I hope I am wrong, but the I do not think the heat gets to be included in the demand factors for this application.

35500-7500=28000

8000va@100%=8000va
20000va@40%=8000va
7500va@100%=7500va
23500va/240v=97.8a

 

[chris kennedy]

I hope I am wrong, but the I do not think the heat gets to be included in the demand factors for this application.

Crap, your right.

 

[jumper]

1200ft? @ 3VA =3600
2 Sm. App @ 1500 = 3000
Laundry = 1500
Range = 8000
WH= 3500
Dryer=3000

Total =22,600

10,000@ 100% = 10,000
12,600@ 40%= 5,040

Total =15,040

New 7.5kw heat = 7.500

Total = 22,540

22,540?240= 94A

First calc looks correct, although, like the others, I was surprised at the WH and dryer nos, like the others.

I'm pleased to see that since I have 2 signed and notarized copies of the following being picked up tonight. Does this look OK?

Load calc for addition of new central AC to existing 100A
service. As per 220.83(B).

1200ft? @3VA = 3,600
2 Sm. App. @1500VA = 3,000
Laundry =1,500
Range = 10,400
WH = 4,500
Dryer = 5,000
New heat = 7,500
Total =35,500 VA

8,000 @ 100% =8,000
27,500 @ 40% =11,000

TOTAL =19,000

19,000 ? 240 = 79 Amps

WH and dryer nos are more typical, range is higher. You now are including heat to the demand factors, I do not think you can.