Sizing a service load

[Bballfan1700]

Hey all, I'm having a bit of difficulty solving this question. As follows:

Using the standard method, calculate the service load for a 2,200 sq ft single family dwelling containing the following loads: range 14kW at 240, dryer 4.20 kW at 240V, dishwasher 1.20 kVA at 120V, waste disposer ¼ hp at 120V, water heater 4.20 kW, A/C two units 12A at 120V, electric heat 6 kW at 240V, and attic fan 1 ½ hp at 120V.

• 142A
• 133A
• 160A
• 130A

As many times as I've done it keep getting 119A, which isn't close to any of the answers above, not sure if I'm getting air conditioner and water heater flip flopped? I assumed I go based off the water heater 100% since there's one. Maybe it's something else I'm not getting? Thanks for your help in advance!

 

[Dennis Alwon]

I agree, I get 113 amps because I took 75% for 4 or more appliances

 

[david luchini]

I get 141A...assume its 142 with rounding.

Don't forget the 75% four the 4 appliances as Dennis mentioned.
The range is 9.6kw.
The dryer is 5kw.
The heat is 6kw. (Larger than the AC)
The lighting, small appliance and laundry is 11.1kw total...3kw at 100% and 8.1kw at 35% (2.835kw.)

Total is 33.89kw, or 141A @ 240V

 

[Dennis Alwon]

David I think the range is 8.8 kw not 9.6

 

[david luchini]

David I think the range is 8.8 kw not 9.6

Thanks, Dennis. I was going by memory and thought it was 5% for each additional 0.5 kW.

That puts me at 138A, which doesn't really correspond with any of the choices. Maybe I'm forgetting something else.

 

[david luchini]

I think that the question askers forgot the 75% for the four appliances. I get 142A when you don't apply the 75% appliance demand factor.

 

[infinity]

As many times as I've done it keep getting 119A, which isn't close to any of the answers above, not sure if I'm getting air conditioner and water heater flip flopped? I assumed I go based off the water heater 100% since there's one. Maybe it's something else I'm not getting? Thanks for your help in advance!

Can you show your math, maybe we can spot the error if there is one.

 

[Dennis Alwon]

I think that the question askers forgot the 75% for the four appliances. I get 142A when you don't apply the 75% appliance demand factor.

I don't know how you are getting that high. I found an error in mine as I used amps instead of VA but I still only get 28,935 or 121 amps

2835 Va for part 1
6300 Va for appliances- I used 600va for disp and 2400 for fan
5000 Va for Dryer
8800 Va for range
6000 va for heat

Total 28935 VA

What am I missing

 

[Dell3c]

2200 x 3 = 6600
3000va- SA (1200va dish) (696va waste) (4200 Water heater) (attic fan 2400va x1.25=3000va)
1500va- LA (1200va + 696va + 4200va +3000va) = 9096va x 0.75= 6822va
8800 range
6000 heat
6822va
+ 5000 dryer
= 37722va /240v = 157.175 (157amperes)

 

[Dennis Alwon]

2200 x 3 = 6600
3000va- SA (1200va dish) (696va waste) (4200 Water heater) (attic fan 2400va x1.25=3000va)
1500va- LA (1200va + 696va + 4200va +3000va) = 9096va x 0.75= 6822va
8800 range
6000 heat
6822va
+ 5000 dryer
= 37722va /240v = 157.175 (157amperes)

That is not correct. You have to take 6600 and add 3000 for small appliance branch circuit and 1500 for Laundry. Take the first 3000 at 100% and the rest at 35%. Then you add the rest-- appliances at 75%

 

[Dell3c]

..."good catch Dennis" : -)

 

[david luchini]

I don't know how you are getting that high. I found an error in mine as I used amps instead of VA but I still only get 28,935 or 121 amps

2835 Va for part 1
6300 Va for appliances- I used 600va for disp and 2400 for fan
5000 Va for Dryer
8800 Va for range
6000 va for heat

Total 28935 VA

What am I missing

It should be 5835 for Part I.

And I'm not sure how you are getting 6300 for appliances.

 

[Dennis Alwon]

Well I used 2400 for attic fan should be 3000 but that doesn't make much difference. I used 600 for disposal based on art 430.

1200 + 600 +4200+2400= 8,400 X 75% = 6300

 

[Dennis Alwon]

It should be 5835 for Part I.

Yep my spreadsheet has an oops Thanks

 

[david luchini]

Yep my spreadsheet has an oops Thanks

I had an oops as well.

So the appliances at 75% (without the 25% for largest motor) would put the answer at 133A.

I've used 696va for the disposal, like Dell3c did.

 

[electrofelon]

Apparently we don't have anyone on here who can get calcs right the first time

I'm not even going to try, that way I can just sit back and make fun of y'all and pretend I would have gotten it right

 

[Dell3c]

2200 x 3 = 6600
6600 (1200va + 696va + 4200va + 2400va x 0.75)=6375va
3000 SA
1500 LA
=(11,100va)
-3000
= 8100
x 0.35
2835va
+3000
=5835va
(5835va +6375va +5000va +8800va + 6000va)=32010 /240v =133.375 (133 amperes)