Why does the Optional Calculation provide a different result?

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bjhuffine said:
My bad, I think I posted on top of you...

5.5kW is the total connected watts on the nameplate
The Dryer nameplate shows 26A and its 240V
No heater on whirlpool.

And again thank you very, very much! :)
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I left code book in truck, I will run numbers in morning and post results.

I think you are doing fine and we forgot, WELCOME to the forum!!!!
 
Using your numbers I come up with 151A.

I think you are over thinking the calc. You engineer you.:grin:

I didn't add in your receptacle load beyond Art 210 or lighting load beyond 210, or vent fan.
 
Are you able to contact your POCO and ask them what your peak usage is?

You could do that and figure out what your max consumption is.

Our POCO's have TOU meters that read peak usage and bill of of that.
 
Chamuit said:
Using your numbers I come up with 151A.

I think you are over thinking the calc. You engineer you.:grin:

I didn't add in your receptacle load beyond Art 210 or lighting load beyond 210, or vent fan.
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Using the Optional or other?

Oh, and by the way... I'm sure it's not the first time I try to overthink a problem... LOL
 
bjhuffine said:
Cool deal...

Square Footage: Living: 1940 sq-ft (per measurement of outside dimensions of space), +260 sq-ft of space in crawl space to be closed in for small workshop.

Bathrooms - 3
Laundry - 1
Attic Space - 1
Crawl Space with access - 1
Water Heater: 240V, 5.5kW
Range: 8kW (per Column C of T220.55)
Refrigerator: 11.2A, 120V... I used 12A (80% loading rule) since this item is replaceable. Though on an exam question, the 11.2 A would have to be used.
Dishwasher: 9.0A, 120V
Microwave/Range Hood combo unit: 1kW
Dryer: 240V/26A: 6.24kW
Garage Door Opener: All I could find on the rating was 1/2hp, so per T430.248: 9.8A @ 120V. And per 430.24, 1.25*9.8*120=1470VA

Receptacle Load beyond those Required in Article 210:
1 in garage + 1 run outside to garden + 8 in workshop area

Lighting Load beyond those Required in Article 210:
1 in Kitchen (non-linear rated 204 VA)
6 in crawlspace and workshop area

Additional Fixed Load:
3 bathroom ventilation fans @1.17A each, 120V
1 whirlpool tub whose motor is rated 7A for 120V, 840VA

HVAC:

Unit 1: Package Gas Furnace and A/C: Min Ckt Ampacity: 17.9A @240V
Unit 2: Split Unit Heat Pump:
Outdoor Unit: Min Ckt Ampacity: 14.1A @240V
Indoor Unit: Min Ckt Ampacity: 33.5A @240V for blower + 8kW auxilliary heat.

With the Artical 220 Parts I-III I get 227A, with Part IV (Optional) I get 160A. Though I didn't include the workspace in the sq-ft calc and am wondering if I should've.
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Some thing you list are not relevant to the calculation, so I'm wondering why you listed them. Example: bathrooms, attic, and receptacles in garage, outside, and workshop.

Where are your two kitchen small appliance circuits? The fridge can be on it. Did you do a laundry circuit?The should each be 150 VA.

If you're doing the Optional calc, the range goes in at full nameplate. If using the standard, it can go per 220.55 col C.

What loads did you apply a 125% factor to for being continuous?
The HVAC should be 100% of nameplate. Which nameplate value I'm not sure of, but MCA is the worst case. Hopefully, you didn't apply a 125% factor here again, since it is built into MCA.
 
Square Footage: Living: 1940 sq-ft , +260 sq for small workshop.=6.6 kW


Laundry - 1.5kw
SABC-3kW

Water Heater: , 5.5kW
Range: 8kW Need Name plate, I will use this for Optional Calc.
[Refrigerator: 11.2A, 120V Include with SABC 220.52
Dishwasher: 9.0A, 120V,1.08kW
Microwave/Range Hood combo unit: 1kW
Dryer: 6.24kW
Garage Door Opener: All I could find on the rating was 1/2hp, so per T430.248: 9.8A @ 120V. And per 430.24, 1.25*9.8*120=1470VA


I think this stuff is included in general lighting load
Lighting Load beyond those Required in Article 210:
1 in Kitchen (non-linear rated 204 VA)
3 bathroom ventilation fans @1.17A each, 120V

Additional Fixed Load:

1 whirlpool tub whose motor is rated 7A for 120V, 840VA

HVAC:

Unit 1: Package Gas Furnace and A/C: Min Ckt Ampacity: 17.9A @240V=4.296kW
Unit 2: Split Unit Heat Pump:
Outdoor Unit: Min Ckt Ampacity: 14.1A @240V=3.384kW
Indoor Unit: Min Ckt Ampacity: 33.5A @240V for blower + 8kW auxilliary heat.=8.04kW

You did not specify one or the other units, so I am counting both. total =15.684 kW
With the Artical 220 Parts I-III I get 227A, with Part IV (Optional) I get 160A. Though I didn't include the workspace in the sq-ft calc and am wondering if I should've.

I came up with 149 amps using the optional calc.
 
The code permits the optional method, it usually results in a lower (and more realistic) calculation, and I use it happily.

Why ask why? ;)
 
suemarkp said:
Some thing you list are not relevant to the calculation, so I'm wondering why you listed them. Example: bathrooms, attic, and receptacles in garage, outside, and workshop.

Where are your two kitchen small appliance circuits? The fridge can be on it. Did you do a laundry circuit?The should each be 150 VA.

If you're doing the Optional calc, the range goes in at full nameplate. If using the standard, it can go per 220.55 col C.

What loads did you apply a 125% factor to for being continuous?
The HVAC should be 100% of nameplate. Which nameplate value I'm not sure of, but MCA is the worst case. Hopefully, you didn't apply a 125% factor here again, since it is built into MCA.
Click to expand...

Some of the spaces, I just listed for informational purposes. The attic, garage, etc. type spaces were because in many of these cases the NEC requires at least one lighting outlet, etc. So again, informational purposes.

This is existing, and yes may not be up to code, but for my calculations I do include the two 1500VA small appliance circuits. I also include a 1500VA laundry circuit as well. As for the MCA, that was a lesson I just learned recently. Otherwise I would've added the 125% factor. But for now I assumed it to have already been included.

As for the refrigerator, Article 210.52(B)(1)(Exception No 2) states that a receptacle outlet for a refrigerator can be supplied from an individual branch circuit rated 15 amperes or more. The key here is the "individual branch circuit" which means that it cannot be shared with a 20A small appliance branch circuit.

Thanks for your input!
 
jumper said:
I think this stuff is included in general lighting load
Lighting Load beyond those Required in Article 210:
1 in Kitchen (non-linear rated 204 VA)
3 bathroom ventilation fans @1.17A each, 120V

Additional Fixed Load:

1 whirlpool tub whose motor is rated 7A for 120V, 840V
Click to expand...

You bring up a good point here that I struggled with. The NEC states required receptacles, branch circuits, and lighting outlets. So my original take on this was that the T220.12 value of 3VA/sq-ft is based on the minimum requirements specified. And since the NEC does provide loading type calculational information for more individual circumstances (such as 180VA per receptacle on a single yoke, rating of luminaire, etc) that it should be added separately. Is this incorrect?

And also, good catch on the range rating (which I forgot to mention is 10.2kW). I had assumed the Optional to be the same as the former in that Column C of T220.55 could be used. Bad assumption on my part, good catch on yours.
 
bjhuffine said:
As for the refrigerator, Article 210.52(B)(1)(Exception No 2) states that a receptacle outlet for a refrigerator can be supplied from an individual branch circuit rated 15 amperes or more. The key here is the "individual branch circuit" which means that it cannot be shared with a 20A small appliance branch circuit.
Click to expand...

I spoke before reading ahead. My apologies. For some reason, I was thinking the refrigerator had to be on a separate circuit. But you're right, it can be shared on the 20A Small Appliance circuit. My bad... it was right there in black and white... Thanks!
 
I don't believe you ever use the 180 VA/yoke on residential load calcs or the max luminare rating. The luminare branch circuit may need to take that into consideration, but that's it. Receptacles are either covered in the square footage value, or their intended dedicated load.

The fact that certain circuits are required doesn't mean they have any load in the service or feeder calcualtion. The bathroom circuit must be 20A, but it has no specific load in the calculation (it is part of the 3 VA/ sq foot). Same with basements, garages, and the outside receptacle.
 
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