Demand Load Calculations

sirsparksalot · 05-10-2011, 01:47 AM

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%.

NJMarine · 05-10-2011, 06:27 AM

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 220-3(a)
Total square footage of habitable living area: __________ @3 watts per sq. foot = _________ watts
Article 220-16(a)
Two small appliance branch circuits @ 1500 watts each: 2 @ 1500 watts each = 3000 watts
Article 220-16(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 220-11
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 220-17
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 220-18 5000 watts or name plate rating: (Whichever is Larger)

Dryer Total = _________watts

WATER HEATER

(If Electric)

Article 220-3(b) @ Nameplate Rating:

Water Heater Load = _________watts

HOUSEHOLD COOKING EQUIPMENT
Table 220-19 Cooking Units-Includes 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 220-4(a) Air conditioner nameplate rating @ 125%: ________watts x 125% = _________watts

OR

Article 220-15 Electric Heat nameplate rating @ 100%: ________watts x 100% = _________watts

(Whichever is Larger)

HEAT PUMP
Article 220-4(a) Largest condensing unit nameplate @ 125%:________ watts @ 125% = ________watts
Article 440-33

AND

Article 220-15 Supplementary heat (resistance) @ 100%: __________watts @ 100% = ________watts
ADDITIONAL HVAC EQUIPMENT
Article 440-33 Condensing units or A/C @ 100%: __________watts @ 100% = ________watts
SPACE HEATING/AIR CONDITIONING TOTAL= ___________watts
OPTIONAL EQUIPMENT
Article 220-3(b) Swimming Pool and/ or
Spa and Article 430-24 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 220-3(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 220-10 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

HouseHelper · 05-10-2011, 10:12 AM

Caldwell is using the optional calculation method for a dwelling (see Section III of Article 220), so his numbers are correct.

sirsparksalot · 05-10-2011, 06:31 PM

Well, I've looked at Section III, and I don't find anything about the first 10000 @ 100%

sirsparksalot · 05-10-2011, 06:33 PM

III. 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
load calculated for general illumination. They shall
not be applied in determining the number of branch circuits

for general illumination.

sirsparksalot · 05-10-2011, 06:40 PM

I'm trying to attach an image of table 220.42. I hope it uploaded

sirsparksalot · 05-10-2011, 06:42 PM

The above is showing that only the first 3000va is allowed/required to go at 100%.??

05-10-2011, 01:47 AM	#1
sirsparksalot Member Join Date: Oct 2010 Location: Central Indiana (USA) Posts: 1,022	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%.

05-10-2011, 06:27 AM	#2
NJMarine Lic Elect/Inspector/CPO Join Date: Apr 2011 Location: NJ Posts: 369	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 220-3(a) Total square footage of habitable living area: __________ @3 watts per sq. foot = _________ watts Article 220-16(a) Two small appliance branch circuits @ 1500 watts each: 2 @ 1500 watts each = 3000 watts Article 220-16(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 220-11 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 220-17 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 220-18 5000 watts or name plate rating: (Whichever is Larger) Dryer Total = _________watts WATER HEATER (If Electric) Article 220-3(b) @ Nameplate Rating: Water Heater Load = _________watts HOUSEHOLD COOKING EQUIPMENT Table 220-19 Cooking Units-Includes 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 220-4(a) Air conditioner nameplate rating @ 125%: ________watts x 125% = _________watts OR Article 220-15 Electric Heat nameplate rating @ 100%: ________watts x 100% = _________watts (Whichever is Larger) HEAT PUMP Article 220-4(a) Largest condensing unit nameplate @ 125%:________ watts @ 125% = ________watts Article 440-33 AND Article 220-15 Supplementary heat (resistance) @ 100%: __________watts @ 100% = ________watts ADDITIONAL HVAC EQUIPMENT Article 440-33 Condensing units or A/C @ 100%: __________watts @ 100% = ________watts SPACE HEATING/AIR CONDITIONING TOTAL= ___________watts OPTIONAL EQUIPMENT Article 220-3(b) Swimming Pool and/ or Spa and Article 430-24 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 220-3(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 220-10 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 Last edited by NJMarine; 05-10-2011 at 06:30 AM.

05-10-2011, 10:12 AM	#3
HouseHelper Licensed Pro Join Date: Mar 2007 Location: SC Posts: 1,439	Demand Load Calculations Caldwell is using the optional calculation method for a dwelling (see Section III of Article 220), so his numbers are correct. __________________ "Life is hard. Life is harder when you're stupid." John Wayne

05-10-2011, 06:31 PM	#4
sirsparksalot Member Join Date: Oct 2010 Location: Central Indiana (USA) Posts: 1,022	Demand Load Calculations Well, I've looked at Section III, and I don't find anything about the first 10000 @ 100%

05-10-2011, 06:33 PM	#5
sirsparksalot Member Join Date: Oct 2010 Location: Central Indiana (USA) Posts: 1,022	Demand Load Calculations III. 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 load calculated for general illumination. They shall not be applied in determining the number of branch circuits for general illumination. Last edited by sirsparksalot; 05-10-2011 at 06:40 PM.

Demand Load Calculations