# House - Standard Load Calculation - Need Help



## JoeyP (Mar 10, 2011)

I'm an apprentice, my license electrician Journeymen handed me the Standard Load Calculation form for a job I'm working on. It's an existing home, with a 150 Amp Service. He wants to see if I can sink or swim. I have no training or education on the load calculation, I spent the past 8 hours with the 2008 NEC (will get 2011 with classes in spring)... this is where I'm at. Any help would be greatly appreciated.

Any links to "example" standard load calculations would be great.

1. General Lighting : Table 220.12

3450 square feet X 3 VA = 10,350 VA
1500VA (small appliance) x 2 = 3,000 VA 
1500VA (laundry) x 1 = 1,500 VA

Total 14,850 VA

First 3,000 VA @ 100% = 3,000 VA
Next 11,850 VA @ 35% = 4,148 VA

Total 7,148 VA
Total Phase__________? VA
Total Neutral ________? VA

--------------------------------------------------------

2. Fixed Appliances: 250.53

Dishwasher = 168 VA ---> 1.4 amps
Disposal = 972 VA ----> 8.1 amps
Total = 1140 VA

1140 VA x 75% = 855 VA

_______? VA Phase 
_______? VA Neutral (120 V loads at 75%)

--------------------------------------------------------

3. Dryer:220.53; 220.53

It's a mini size dryer, rated at 12 amps or 2880 VA. But codes says "5000 VA or name plate rating, which ever is larger".

5,000 VA x 100% = 5,000 VA

_______? VA Phases
_______? VA Neutral x 70%

------------------------------------------------------------

4. Cooking Equipment: Table 22.55; Notes

I'm totally lost here... with col. A, B, C

Cooktop 7 Kv = 7,000 VA
Oven 3.7 Kv = 3,700 VA

Col A _______ VA x _______% = _______ VA
Col B _______ VA x _______% = _______ VA
Col C _______ VA x _______% = _______ VA

_______? VA Phase
_______? VA Neutral x 70%

-----------------------------------------------------------

5. Heating or A/C: 220.60

A/C = 5,280 VA x 100% = 5,280 VA

______? VA Phase
______? VA Neutral

-----------------------------------------------------------

6. Largest Motor

I don't understand this... I did my A/C above.

------------------------------------------------------------

Phases I = ___ VA / ___ V = ___ A
Neutral I = ___ VA / ___ V = ___ A

____ VA Phases
____ VA Neutral

220.61(B) First 200 A x 100% = 200 A
Remaining ____ A x 70% =


----------



## HARRY304E (Sep 15, 2010)

Welcome to the forum...:thumbsup: Theses formulas will help..


----------



## Rockyd (Apr 22, 2007)

Check your Mail box...that pie won't do a thing for you that Harry threw on the board...


----------



## JoeyP (Mar 10, 2011)

Rocky I didn't have excel on this computer, but will try it from a different computer tonight.

I'm still a bit confused on the Cooking Equipment. Cook top 7 Kv (7000 VA)& Oven 3.7 Kv (3700 VA). I didn't know which column A, B or C to use. I found some better examples in the NEC Annex D, I'm doing all the examples to get the hang of it.

And I didn't know what to do with "6. Largest Motor" cause that would be my AC, which is calculated for in "5. Heating & AC".

I'm gonna keep reading, it's starting to make more sense to me as I go along. Thanks guys.


----------



## raider1 (Jan 22, 2007)

> 4. Cooking Equipment: Table 22.55; Notes
> 
> I'm totally lost here... with col. A, B, C
> 
> ...


Joey, when using Table 220.55 the example you have you would have 2 appliances that fall under Column B (31/2 through 83/4 Kw rating)

So you would add up the 7,000 and 3,700 and apply the factor listed in Column B for 2 appliances which would be 65%.

So you would take 10,700 and multiply it by .65 and get a cooking load of 6,955 watts.

As for the largest motor load that would exclude the A/C unit as the A/C unit is already included for the larger of the heat or A/C load.

Chris


----------



## JohnR (Apr 12, 2010)

JoeyP said:


> I'm an apprentice, my license electrician Journeymen handed me the Standard Load Calculation form for a job I'm working on. It's an existing home, with a 150 Amp Service. He wants to see if I can sink or swim. I have no training or education on the load calculation, I spent the past 8 hours with the 2008 NEC (will get 2011 with classes in spring)... this is where I'm at. Any help would be greatly appreciated.
> 
> Any links to "example" standard load calculations would be great.
> 
> ...


I hope this helps, and welcome to the forum.


----------



## Rockyd (Apr 22, 2007)

JoeyP said:


> Rocky I didn't have excel on this computer, but will try it from a different computer tonight.
> 
> I'm still a bit confused on the Cooking Equipment. Cook top 7 Kv (7000 VA)& Oven 3.7 Kv (3700 VA). I didn't know which column A, B or C to use. I found some better examples in the NEC Annex D, I'm doing all the examples to get the hang of it.
> 
> ...


Follow Chris's lead(Raider1) and - Welcome to the Forum! :thumbsup: Smartest electrical place on the web (just ask anyone in here):thumbup: Good place for lots of things!


----------



## nitro71 (Sep 17, 2009)

What cooking appliances do you have? If you have only one, off the top of my head seems like 8000 watts? Can't quote me on that.


----------



## Rockyd (Apr 22, 2007)

nitro71 said:


> What cooking appliances do you have? If you have only one, off the top of my head seems like 8000 watts? Can't quote me on that.


12Kw gets you 8Kw for your calculation...

220.55 "Notes" almost deserves a chapter!:whistling2:

Cool JohnR:thumbsup:


----------



## raider1 (Jan 22, 2007)

nitro71 said:


> What cooking appliances do you have? If you have only one, off the top of my head seems like 8000 watts? Can't quote me on that.


If you only have 1 appliance between 8 3/4 Kw and 12 Kw then the calculated load would be 8 Kw in accordance with Coulmn C Table 220.55.



Rockyd said:


> 12Kw gets you 8Kw for your calculation...
> 
> *220.55 "Notes" almost deserves a chapter!:whistling2:*
> 
> Cool JohnR:thumbsup:


I agree 100%.

When I teach on dwelling unit calculations Table 220.55 is by far the bulk of the class.

Chris


----------



## JoeyP (Mar 10, 2011)

Thanks for the overwhelming response. I think I've got it correct now, let me know if it looks about right.



1. General Lighting : Table 220.12

3450 square feet X 3 VA = 10,350 VA
1500VA (small appliance) x 2 = 3,000 VA
1500VA (laundry) x 1 = 1,500 VA
-----
Sum Total 14,850 VA


First 3,000 VA @ 100% = 3,000 VA
Next 11,850 VA @ 35% = 4,148 VA
------
Sum Total = 7,148 VA

Total Phase = 7,148 VA
Total Neutral = 7,148 VA

--------------------------------------------------------

2. Fixed Appliances: 250.53

Dishwasher = 168 VA
Disposal = 972 VA
Cloth Washer = 1440 VA
------
Sum Total = 2580 VA


2580 VA x 75% = 1935 VA


1935 VA Phase
1451 VA Neutral @ 75% (1935 VA x 75% = 1451 VA)

--------------------------------------------------------

3. Dryer:220.53; 220.53

5,000 VA x 100% = 5,000 VA

5,000 VA Phases
3,500 VA Neutral @ 70% (5,000 VA x 70% = 3,500 VA)

------------------------------------------------------------

4. Cooking Equipment: Table 22.55; Notes

10,700 VA x 65% = 6955 VA 

6955 VA Phase
4869 VA Neutral @ 70% (6955 VA x 70% = 4869 VA)

-----------------------------------------------------------

5. Heating or A/C: 220.60

5,280 VA x 100% = 5,280 VA

5,280 VA Phase
5,280 VA Neutral

-----------------------------------------------------------

6. Largest Motor

(/) 5,280 VA x 25% = 1,320 VA
N 5,280 VA x 25% = 1,320 VA

1,320 VA Phase
1,320 VA Neutral


------------------------------------------------------------

Sum Phases = 27,638 VA

Phases I = ___ VA / ___ V = ___ A

27,638 VA / 240 Volts = 115 Amps

-------

Sum Neutral = 23,568 VA

Neutral I = ___ VA / ___ V = ___ A

23,568 VA / 240 Volts = 98 Amps

Phases = 115 Amps
Neutral = 98 Amps

I should not be overloading a 150 amp service, assuming 120 amps is the safety mark.


----------



## nitro71 (Sep 17, 2009)

The number you get in amps is the NEC required service size. You can put a larger one in for future expansion or just because you want to but there's no requirement to plan for it.


----------



## NolaTigaBait (Oct 19, 2008)

I'm spoiled, I use Mike Holts resi load calculator...:jester:


----------



## raider1 (Jan 22, 2007)

Couple of problems Joey,



> 2. Fixed Appliances: 250.53
> 
> Dishwasher = 168 VA
> Disposal = 972 VA
> ...


You can't use the 75% demand factor until you have 4 or more appliances. For 3 appliances you must use the total added load.



> . Largest Motor
> 
> (/) 5,280 VA x 25% = 1,320 VA
> N 5,280 VA x 25% = 1,320 VA
> ...


You don't need to add the A/C unit again.

Chris


----------

