ECN Forum Forums Code Related Discussion NEC & other Code issues Service Calcs

Try the caculator at this site. http://www.electricalknowledge.com/SFDLoadCalc.asp
You said "the compressor gets a 40A disco and the unit above the garage gets a 60 breaker. this is a heat pump made by trane..
the compressor runs until the heat strips come on then the compressor is shut off."
You need to verify this. I have a Trane and the compressor runs til the temp get below 32F and then the strips come in. Both are on at the same time.

The heat load seems to be about 12kw. Take the 60 amp breaker x .80 = 48amps.
48 amps x 240 =11.5 kw. The compressor load
is 40amp x .80 = 32 amps x 240 = 6144 va.
You may have a central electric furnace and A/C. If so 220.30C4 applies. Try the caculator and give us the results.

Hello,.

Couple quick questions..

I have a 200A main panel outside with feed through lugs..

Can i feed a 100A sub panel from the feed though lugs? There is a 100A main breaker in the sub panel.

I also decided to split the load on this house..

I am feeding the 60A Heat from the main 200A panel with a 60 A. I felt that this would reduce the total load on the 100A panel and that would save me from removing the 100A panel that is already installed..I just refed the heat from the 100A to the 200A ..

I calculted the load on the sub panel just like I would for a main service right? Or would there be a different calc for the sub panell since it is no longer the main?

Here is the load I got for the 100A sub panel..

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General Light and Receptacle Load
1308sqft x 3VA = 3924VA
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Small Appliance Circuits Load
2 x 1500VA = 3000VA
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Laundry Branch Circuit(s) Load
1 x 1500VA = 1500VA
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Total General Load Less Demand
sum of above less T220.11 demand
sum of above = 8424VA
first 3000 at 100 % = 3000
next 117,000 at 35% = 1898
remainder at 25% = 0
sum less demand = 4898VA
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Fastened In Place Appliances Load
Disposal = 1000VA
Water Heater = 4800VA
Garage Door = 1000VA
Dish Washer = 1600VA
Attic Fan = 500VA
Microwave = 975VA
sum less 75% demand = 7406VA
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Clothes Dryer Circuit(s)Load
Total dryer circuit(s) load = 5000VA
--------------------------------------------------------------------------------
Cooking Appliance(s) Load
T220.19 Column A = 0kVA
T220.19 Column B = 0kVA
T220.19 Column C = 0kVA
Total calc.d range load = 0kVA
--------------------------------------------------------------------------------
Heating or Air-Conditioning Load
Air Conditioner = 4585VA
--------------------------------------------------------------------------------
Largest Motor Load
25% of largest motor = 1000VA
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Total Computed Load
22889 Volt-Amps
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Computed Amperage
22889 divided by 240 = 95Amps Neutral Loads
General Neutral Load = 4898VA
--------------------------------------------------------------------------------
Fastened In Place Appliances Neutral Load
Disposal = 1000VA
Garage Door = 1000VA
Dish Washer = 1600VA
Attic Fan = 500VA
Microwave = 975VA
Total before 75% demand(4 or more) = 5075VA
Total FIP Neutral Load = 3806VA
--------------------------------------------------------------------------------
Clothes Dryer Neutral Load
220.22 allows 70% of 5000VA
Clothes Dryer Neutral Load = 3500VA
--------------------------------------------------------------------------------
Cooking Appliances
220.22 allows 70% of 0VA
Cooking Appliances Neutral Load = 0VA
--------------------------------------------------------------------------------
Heating or Air Nuetral Load = 0VA
--------------------------------------------------------------------------------
Total Neutral Load = 13204VA
--------------------------------------------------------------------------------
Total Neutral Amperage = 55Amps
--------------------------------------------------------------------------------


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Can anybody help?

Thanks

Bradley
Total Neutral Amperage = 50Amps

[This message has been edited by electcontrctr (edited 04-21-2005).]

I believe hanging a 100A subpanel off of a 200A feed through main panel would be a feeder tap. I think you can meet the rules of 240.21 (B)(2), so you can go 25 feet max with that feeder. Does the subpanel have a #4 copper feeder and a 100A main?

Hi,
The sub panel is 70 feet away and has a main breaker and is fed with 2-2-2-4 AL..there is a #4 cold water bond from the sub.

So I will need a 100A main from the main panel correct? I dont need a main breaker in the sub panel at all do I?

thank you for the help..

Brad

In my opinion, you need the 100-amp breaker in the main panel to protect the feeder, and the sub-panel can be a main-lug, as long as it's not in a separate building.

I would ask to see the 125% rule in writing. If your calc load is 165 A, the 125% would make the load 206 A which means a 400 amp service. The microwave needs to be included only if there is a dedicated cabinet space for the MW. Otherwise the kit small appl circuit will cover it. Use the optional calculation in the NEC. Where is the 125% of largest motor rule? I think that is industrial only.

If your calc load is over 90 A, why not put in s 200 amp service? How much more does it cost? $150, $200 ?