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05102011, 01:47 AM  #1 
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Demand Load Calculations
I'm looking at Rex Cauldwell's Wiring A House, and I have a question about his Demand Factors for lighting. Reference to pp. 52 & 54, if anyone has this book.
In his exampled steps, (for a 2000 SQ FT house) he first determines the General Lighting Load (SF @ 3va. He then adds 3000va for the 2 required small appliance circuit in the kitchen, and then the 1500 Laundry circuit. He then calculates all other appliances (and, excluding the AC and Htg.), and arrives at 30,000W. Totaling all of these together, we come up with 40,000 watts. Now, he states that "[b]ecause all loads do not operate at the same time, take the first 10,000 at face value, then take 40% off the rest:10,000 +[.4(30,000)] = 10,000 +12,000 = 22,000." Question: Is Mr. Cauldwell mistaken here, or am I missing another detail? Table 220.11 says to take the first 3,000 @100%, the rest (up to 120K) at 35%, and the final (over 120K) at 25%. Advertisement 
05102011, 06:27 AM  #2 
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Demand Load Calculations
This long but here how it is done
As you can see, Remainder from 3001watts to 120,000 watts: @ 35% = watts RESIDENTIAL ELECTRICAL LOAD WORKSHEET LIGHTING LOAD Article 2203(a) Total square footage of habitable living area: __________ @3 watts per sq. foot = _________ watts Article 22016(a) Two small appliance branch circuits @ 1500 watts each: 2 @ 1500 watts each = 3000 watts Article 22016(a) Additional small appliance circuits each: @ 1500 watts each = _____ watts Article 220 16(b) Laundry circuit @ 1500 watts each: @ 1500 watts each = _____ watts Lighting Load Subtotal = _____ watts Table 22011 First 3000 watts of lighting load: __________ @ 100% = 3000 watts Remainder from 3001watts to 120,000 watts: __________ @ 35% = __________ watts Remainder over 120,000 watts: __________ @ 25% = __________ watts Lighting Load Total = ___________watts APPLIANCE LOAD Article 22017 Garbage disposal @ 600 watts each: ____________ @ 600 watts each = __________ watts Microwave @ 1500 watts each: ____________ @ 1500 watts each = __________watts Trash compactor @ 1200 watts each: ____________@ 1200 watts each = __________watts Dishwasher @ 1200 watts each: ____________@ 1200 watts each = __________watts Refrigerator @ 600 watts each: ____________@ 600 watts each = ___________watts Name Plate Rating of Miscellaneous Appliances: ___________________________ @______watts each = __________watts ___________________________ @______watts each = __________watts Appliance Subtotal = ______________watts Appliance subtotal: ____________watts x ____________ = _____________watts (Less than 4 appliances @ 100%; 4 or more appliances @ 75%) ELECTRIC CLOTHES DRYER Article 22018 5000 watts or name plate rating: (Whichever is Larger) Dryer Total = _________watts WATER HEATER (If Electric) Article 2203(b) @ Nameplate Rating: Water Heater Load = _________watts HOUSEHOLD COOKING EQUIPMENT Table 22019 Cooking UnitsIncludes ranges, wall mounted ovens, countertop units, and other household cooking units. Number of Units ONE unit use= 8000 watts TWO unit use = 11,000 watts THREE unit use = 14,000 watts FOUR unit use = 17,000 watts FIVE unit use = 20,000 watts COOKING TOTAL= _________________watts SPACE HEATING/AIR CONDITIONING Article 2204(a) Air conditioner nameplate rating @ 125%: ________watts x 125% = _________watts OR Article 22015 Electric Heat nameplate rating @ 100%: ________watts x 100% = _________watts (Whichever is Larger) HEAT PUMP Article 2204(a) Largest condensing unit nameplate @ 125%:________ watts @ 125% = ________watts Article 44033 AND
Article 22015 Supplementary heat (resistance) @ 100%: __________watts @ 100% = ________watts ADDITIONAL HVAC EQUIPMENT Article 44033 Condensing units or A/C @ 100%: __________watts @ 100% = ________watts SPACE HEATING/AIR CONDITIONING TOTAL= ___________watts OPTIONAL EQUIPMENT Article 2203(b) Swimming Pool and/ or Spa and Article 43024 Largest motor nameplate: ____________watts @ 125% = __________watts Remaining motor(s) nameplate(s): ____________watts @ 100% = __________watts Lights and other miscellaneous equipment: ____________watts @ 100% = __________watts POOL/SPA TOTAL = ______________watts Article 2203(b) Welders, Kilns, Etc. Name or description of equipment @ rated nameplate: ______________watts x 100% =________watts Name or description of equipment @ rated nameplate: ______________watts x 100% =________watts Name or description of equipment @ rated nameplate: ______________watts x 100% =________watts MISCELLANEOUS EQUIPMENT TOTAL = _____________watts TOTAL DEMAND ON SYSTEM Article 22010 Sum of all totals: LIGHTING LOAD TOTAL = _______________WATTS APPLIANCE TOTAL = _______________WATTS DRYER TOTAL = _______________WATTS WATER HEATER TOTAL = _______________WATTS COOKING TOTAL = _______________WATTS SPACE HEATING/AIR CONDITIONING TOTAL = _______________WATTS POOL/SPA TOTAL = _______________WATTS MISCELLANEOUS EQUIPMENT TOTAL = _______________WATTS AdvertisementLast edited by NJMarine; 05102011 at 06:30 AM. 
05102011, 10:12 AM  #3 
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Demand Load Calculations
Caldwell is using the optional calculation method for a dwelling (see Section III of Article 220), so his numbers are correct.
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05102011, 06:31 PM  #4 
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Demand Load Calculations
Well, I've looked at Section III, and I don't find anything about the first 10000 @ 100%

05102011, 06:33 PM  #5 
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Demand Load CalculationsIII. Feeder and Service Load Calculations 220.40 General. The calculated load of a feeder or service shall not be less than the sum of the loads on the branch circuits supplied, as determined by Part II of this article, after any applicable demand factors permitted by Parts III or IV or required by Part V have been applied. FPN: See Examples D1(a) through D10 in Annex D. See 220.18(B) for the maximum load in amperes permitted for lighting units operating at less than 100 percent power factor. 220.42 General Lighting. The demand factors specified in
Table 220.42 shall apply to that portion of the total branchcircuit for general illumination.load calculated for general illumination. They shall not be applied in determining the number of branch circuits Last edited by sirsparksalot; 05102011 at 06:40 PM. 
05102011, 06:40 PM  #6 
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Demand Load Calculations
I'm trying to attach an image of table 220.42. I hope it uploaded

05102011, 06:42 PM  #7 
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Demand Load Calculations
The above is showing that only the first 3000va is allowed/required to go at 100%.??
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