].

70-834 NATIONAL ELECTRICAL CODE Example No. 1(a) (Continued) Neutral for Feeder and Service Lighting and Small Appliance Load 5100 volt-amperes Range Load 8000 volt-amperes at 70% 5600 volt-amperes Dryer Load 5500 volt-amperes at 70% 3850 volt-amperes Total 14,550 volt-amperes 14,550 volt-amperes ÷ 240 Volts = 60.6 amperes Example No. 1(b). One-Family Dwelling Same conditions as Example No. 1(a), plus addition of one 6-ampere 230-volt room air-conditioning unit and one 12-ampere 115-volt room airconditioning unit,* one 8-ampere 115-volt rated disposal and one 10-ampere 120-volt rated dishwasher.* See Article 430 for general motors and Article 440, Part G, for air-conditioning equipment. Motors have nameplate ratings of 115 V and 230 V for use on 120 V and 240 V nominal voltage systems. From previous Example No. 1(a), feeder current is 78 amperes (3-wire, 240 volts). Line A Neutral Line B Amperes from Example No. 1(a) 78 61 78 One 230-V air conditioner 6 - 6 One 115-V air conditioner and 120-V dishwasher 12 12 10 One 115-V disposal - 8 8 25% of largest motor (Section 430-24) 3 3 2 Amperes per line 99 84 104 * For feeder neutral, use largest of the two appliances for unbalance. Example No. 2(a). Optional Calculation for One-Family Dwelling, Heating Larger than Air Conditioning [See Section 220-30(a) and Table 220-30.] Dwelling has a floor area of 1500 sq. ft., exclusive of unoccupied cellar, unfinished attic, and open porches. It has a 12-kW range, a 2.5-kW water heater, a 1.2-kW dishwasher, 9 kW of electric space heating installed in five rooms, a 5-kW clothes dryer, and a 6-ampere 230-volt room airconditioning unit. Assume range, water heater, dishwasher, space heating, and clothes dryer kW ratings equivalent to kVA. Air conditioner kVA is 6 X 230 ÷ 1000 = 1.38 kVA 1.38 kVA is less than the connected load of 9 kVA of space heating; therefore, the air conditioner load need not be included in the service calculation (see Section 220-21). 1500 sq. ft. at 3 volt-amperes 4500 volt-amperes Two 20-ampere appliance outlet circuits at 1500 volt-amperes each 3000 volt-amperes Laundry circuit 1500 volt-amperes Range (at nameplate rating) 12,000 volt-amperes Water heater 2500 volt-amperes Dishwasher 1200 volt-amperes Clothes dryer 5000 volt-amperes 29,700 volt-amperes CHAPTER 9 - TABLES AND EXAMPLES 70-835 Example No. 2(a) (Continued) First 10 kVA of other load at 100% = 10,000 volt-amperes Remainder of other load at 40% (19.7 kVA X .4) = 7900 volt-amperes Total of other load = 17,900 volt-amperes 9 kVA of heat at 40% (9 X .4) = 3600 volt-amperes Total load = 21,500 volt-amperes Calculated load for service size 21.5 kVA = 21,500 volt-amperes 21,500 VA ÷ 240 volts = 90 amperes Therefore, this dwelling shall be permitted to be served by a 100-ampere service. I Feeder Neutral Load, per Section 220-22: 1500 sq. ft. at 3 volt-amperes 4500 volt-amperes Three 20-amp. circuits at 1500 volt-amperes 4500 volt-amperes Total 9000 volt-amperes 3000 volt-amperes at 100% 3000 volt-amperes 9000 VA-3000 VA = 6000 volt-amperes at 35% 2100 volt-amperes 5100 volt-amperes Range - 8 kVA at 70% 5600 volt-amperes Clothes dryer - 5 kVA at 70% 3500 volt-amperes Dishwasher 1200 volt-amperes Total 15,400 volt-amperes 15,400 volt-amperes ÷ 240 volts = 64.2 amperes Example No. 2(b). Optional Calculation for One-Family Dwelling, Air Conditioning Larger than Heating [See Section 220-30(a) and Table 220-30.] Dwelling has a floor area of 1500 sq. ft., exclusive of unoccupied cellar, unfinished attic, and open porches. It has two 20-ampere small appliance circuits, one 20-ampere laundry circuit, two 4-kW wall-mounted ovens, one 5.1-kW counter-mounted cooking unit, a 4.5-kW water heater, a 1.2-kW dishwasher, a 5-kW combination clothes washer and dryer, six 7-ampere 230-volt room air-conditioning units, and a 1.5-kW permanently installed bathroom space heater. Assume wall-mounted ovens, countermounted cooking unit, water heater, dishwasher, and combination clothes washer and dryer kW ratings equivalent to kVA. Air Conditioning kVA Calculation: Total amperes 6 X 7 = 42.00 amperes 42 X 240 ÷ 1000 = 10.08 kVA of air-conditioned load; assume P.F. = 1.0 Load included at 100%: Air Conditioning (see below) Space heater (omit, see Section 220-21) Other Load: 1500 sq. ft. at 3 volt-amperes 4500 volt-amperes Two 20-amp. small appliance circuits at 1500 volt-amperes 3000 volt-amperes Laundry circuit 1500 volt-amperes Two ovens 8000 volt-amperes One cooking unit 5100 volt-amperes 70-836 NATIONAL ELECTRICAL CODE Example No. 2(b) (Continued) Water heater 4500 volt-amperes Dishwasher 1200 volt-amperes Washer/dryer 5000 volt-amperes Total other load 32,800 volt-amperes 1st 10 kVA at 100% 10,000 volt-amperes Remainder at 40% (22.8 kVA X .4) 9120 volt-amperes Total other load 19,120 volt-amperes Other load 19,120 volt-amperes Air conditioning 10,080 volt-amperes 29,200 volt-amperes 29,200 volt-amperes ÷ 240 volts = 122 amperes (service rating) Feeder Neutral Load, per Section 220-22: (It is assumed that the two 4-kVA wall-mounted ovens are supplied by one branch circuit, the 5.1-kVA counter-mounted cooking unit by a separate circuit.) 1500 sq. ft. at 3 volt-amperes 4500 volt-amperes Three 20-amp. circuits at 1500 volt-amperes 4500 volt-amperes Total 9000 volt-amperes 3000 volt-amperes at 100% 3000 volt-amperes 9000 VA-3000 VA = 6000 volt-amperes at 35% 2100 volt-amperes 5100 volt-amperes Two 4-kVA ovens plus one 5.1-kVA cooking unit totals 13.1 kVA Table 220-19 permits 55% demand factor 13.1 kVA X .55 = 7.2 kVA feeder capacity 7200 volt-amperes X 70% for neutral load 5040 volt-amperes Clothes washer/dryer - 5 kVA X 70% for neutral load 3500 volt-amperes Dishwasher 1200 volt-amperes Total 14,840 volt-amperes 14,840 volt-amperes ÷ 240 volts = 61.83, use 62 amperes Example No. 2(c). Optional Calculation for One-Family Dwelling with Heat Pump Single-Phase, 240/120-Volt Service (See Section 220-30.) Dwelling has a floor area of 2000 sq. ft., exclusive of unoccupied cellar, unfinished attic, and open porches. It has a 12-kW range, a 4.5-kW water heater, a 1.2-kW dishwasher, a 5-kW clothes dryer, and a 21/2-ton (24- ampere) heat pump with 15 kW of back-up heat. Heat pump kVA is 24 X 240 ÷ 1000 = 5.76 kVA. 5.76 kVA is less than 15 kVA of the back-up heat; therefore, the heat pump load need not be included in the service calculation. (See Table 220-30.) 2000 sq. ft. at 3 volt-amperes 6000 volt-amperes Two 20-ampere appliance outlet circuits at 1500 volt-amperes each 3000 volt-amperes Laundry circuit 1500 volt-amperes Range (at nameplate rating) 12,000 volt-amperes Water heater 4500 volt-amperes Dishwasher 1200 volt-amperes Clothes dryer 5000 volt-amperes 33,200 volt-amperes CHAPTER 9 - TABLES AND EXAMPLES 70-837 Example No. 2(c) (Continued) First 10 kVA of other load at 100% = 10,000 volt-amperes Remainder of other load at 40% (23,200 volt-amperes X 0.4) = 9,280 volt-amperes Total of other load = 19,280 volt-amperes Heat pump and supplementary heat* 240 X 24 = 5760 volt-amperes 15-kW electric heat: 5760 volt-amperes + 15,000 volt-amperes = 20,760 volt-amperes or = 20.76 kVA 20.76 kVA at 65% = 13.49 kVA *If supplementary heat is not on at same time as heat pump, heat pump kVA need not be added to total. Totals: Other load 19,280 volt-amperes Heat pump and supplementary heat 13,490 volt-amperes Total 32,770 volt-amperes 32.77 kVA ÷ 240 volts= 136.5 amperes Therefore, this dwelling unit shall be permitted to be served by a 150-ampere service. I Example No. 3. Store Building A store 50 ft. by 60 ft., or 3000 sq. ft., has 30 ft. of show window. There are a total of 80 duplex receptacles. The service is 120/240-volt, singlephase (3-wire service). Actual connected lighting load: 8500 volt-amperes. Computed Load (Section 220-10): Noncontinuous Loads: Receptacle Load (Section 220-13) 80 receptacles at 180 volt-amperes = 14,400 volt-amperes 10,000 VA at 100% 10,000 volt-amperes (14,400-10,000) VA at 50% 2200 volt-amperes Total 12,200 volt-amperes Continuous Loads: General Lighting Load:* 3000 sq. ft. at 3 volt-amperes per sq. ft 9000 volt-amperes Show Window Lighting Load: 30 ft. at 200 volt-amperes per ft. 6000 volt-amperes Outside sign circuit 1200 volt-amperes [Section 600-6(c)] 1200 volt-amperes 16,200 volt-amperes Total noncontinuous loads plus continuous loads 28,400 volt-amperes Minimum Number of Branch Circuits Required: General Lighting Load: Branch circuits need only be installed to supply the actual connected load [Section 220-4(d)]. 8500 volt-amperes X 1.25 = 10,625 volt-amperes 10,625 volt-amperes ÷ 240 volts = 44 amperes for 3-wire, 120/240. The lighting load shall be permitted to be served by 2-wire or 3-wire 15- or 20-ampere circuits with combined capacity equal to 44 amperes or greater for 3-wire circuits or 88 amperes or greater for 2-wire circuits. The feeder capacity as well as the number of branch-circuit positions available for lighting circuits in the panelboard must reflect the full calculated load of 9000 volt-amperes X 1.25 = 11,250 volt-amperes. 70-838 NATIONAL ELECTRICAL CODE Example No. 3 (Continued) Show Window: 6000 volt-amperes X 1.25 = 7500 volt-amperes 7500 volt-amperes ÷ 240 volts = 31 amperes for 3-wire, 120/240. The show window lighting shall be permitted to be served by 2-wire or 3-wire circuits with a capacity equal to 31 amperes or greater for 3-wire circuits or 62 amperes or greater for 2-wire circuits. Receptacles required by Section 210-62 are assumed to be included in the receptacle load above if these receptacles do not supply the show window lighting load. Receptacles: Receptacle Load: 14,400 volt-amperes ÷ 240 volts = 60 amperes for 3-wire, 120/240. The receptacle load shall be permitted to be served by 2-wire or 3-wire circuits with a capacity equal to 60 amperes or greater for 3-wire circuits or 120 amperes or greater for 2-wire circuits. Minimum Size Feeder (or Service) Overcurrent Protection [Section 220-10(b) or Section 230-90(a)]: Total noncontinuous loads Total continuous load @ 125% 12,200 volt-amperes 16,200 X 1.25 20,250 volt-amperes Total load 32,450 volt-amperes 32,450 volt-amperes ÷ 240 volts = 135 amperes The next higher standard size is 150 amperes. (Section 240-6). Minimum Size Feeders (or Service Conductors) Required [Sections 215-3, 220-10(b), 230-42(a)]: For 120/240-volt, 3-wire system: 28,400 volt-amperes ÷ 240 volts = 118 amperes Service or feeder conductor is No. 1 Cu per Table 310-16 (with 75°C terminations). The No. 1 Cu wire is protected by the 150-ampere overcurrent setting per Sections 215-3 [or Section 230-90(a), Exception No. 2] and 240-3(b). In the example, 125 percent of the actual connected lighting load (8500 volt-amperes X 1.25 = 10,625 volt-amperes) is less than 125 percent of the load from Table 220-3(b), so the minimum lighting load from Table 220-3(b) is used in the calculation. Had the actual lighting load been greater than the value computed from Table 220-3(b), 125 percent of the actual connected lighting load would have been used. Example No. 4(a). Multifamily Dwelling Multifamily dwelling having 40 dwelling units. Meters in two banks of 20 each and individual subfeeders to each dwelling unit. One-half of the dwelling units are equipped with electric ranges not exceeding 12 kW each. Assume range kW rating equivalent to kVA rating in accordance with Section 220-19. Other half of ranges are gas ranges. Area of each dwelling unit is 840 sq. ft. Laundry facilities on premises available to all tenants. Add no circuit to individual dwelling unit. Add 1500 volt-amperes for each laundry circuit to house load and add to the example as a "house load." CHAPTER 9 - TABLES AND EXAMPLES 70-839 Example No. 4(a) (Continued) Computed Load for Each Dwelling Unit (Article 220): General Lighting Load: 840 sq. ft. at 3 volt-amperes per sq. ft 2520 volt-amperes Special Appliance Load: Electric Range (Section 220-19) 8000 volt-amperes Minimum Number of Branch Circuits Required for Each Dwelling Unit (Section 220-4): General Lighting Load: 2520 volt-amperes ÷ 120 volts = 21 amperes or two 15-ampere, 2-wire circuits; or two 20-ampere, 2-wire circuits. Small Appliance Load: Two 2-wire circuits of No. 12 wire. [See Section 220-4(b).] Range Circuit: 8000 volt-amperes ÷ 240 = 33 amperes or a circuit of two No. 8 conductors and one No. 10 conductor as permitted by Section 220-22. (See Section 210-19.) Minimum Size Subfeeder Required for Each Dwelling Unit (Section 215-2): Computed Load (Article 220): General Lighting Load 2520 volt-amperes Small Appliance Load: two 20-ampere circuits 3000 volt-amperes Total Computed Load (without ranges) 5520 volt-amperes Application of Demand Factor: 3000 volt-amperes at 100% 3000 volt-amperes 2520 volt-amperes at 35% 882 volt-amperes Net Computed Load (without ranges) 3882 volt-amperes Range Load 8000 volt-amperes Net Computed Load (with ranges) 11,882 volt-amperes Size of Each Subfeeder (see Section 215-3). For 120/240-volt, 3-wire system (without ranges): Net Computed Load, 3882 volt-amperes ÷ 240 volts = 16.2 amperes. For 120/240-volt, 3-wire system (with ranges): Net Computed Load, 11,882 volt-amperes ÷ 240 volts = 49.5 amperes. Subfeeder Neutral: Lighting and Small Appliance Load 3882 volt-amperes Range Load: 8000 volt-amperes at 70% (see Section 220-22) 5600 volt-amperes (Not included for apartments without electric range) Net Computed Load (neutral) 9482 volt-amperes 9482 volt-amperes ÷ 240 volts = 39.5 amperes Minimum Size Feeders Required from Service Equipment to Meter Bank (For 20 Dwelling Units - 10 with Ranges): Total Computed Load: Lighting and Small Appliance Load: 20 X 5520 volt-amperes 110,400 volt-amperes Application of Demand Factor: 3000 volt-amperes at 100% 3000 volt-amperes 107,400 volt-amperes at 35% 37,590 volt-amperes Net Computed Lighting and Small Appliance Load 40,590 volt-amperes Range Load, 10 ranges (less than 12 kVA, Col. A, Table 220-19) 25,000 volt-amperes Net Computed Load (with ranges) 65,590 volt-amperes 70-840 NATIONAL ELECTRICAL CODE Example No. 4(a) (Continued) For 120/240-volt, 3-wire system: Net Computed Load, 65,590 volt-amperes ÷ 240 volts = 273 amperes Feeder Neutral: Lighting and Small Appliance Load 40,590 volt-amperes Range Load: 25,000 volt-amperes at 70% (see Section 220-22) 17,500 volt-amperes Computed Load (neutral) 58,090 volt-amperes 58,090 volt-amperes ÷ 240 volts = 242 amperes Further Demand Factor (Section 220-22): 200 amperes at 100% 200 amperes 42 amperes at 70% 29 amperes Net Computed Load (neutral) 229 amperes Minimum Size Main Feeder (or Service Conductors) Required (less house load). (For 40 Dwelling Units - 20 with Ranges): Total Computed Load: Lighting and Small: Appliance Load: 40 X 5520 volt-amperes 220,800 volt-amperes Application of Demand Factor: 3000 volt-amperes at 100% 3000 volt-amperes 117,000 volt-amperes at 35% 40,950 volt-amperes 100,800 volt-amperes at 25% 25,200 volt-amperes Net Computed Lighting and Small Appliance Load 69,150 volt-amperes Range Load, 20 ranges (less than 12 kVA, Col. A, Table 220-19) 35,000 volt-amperes Net Computed Load 104,150 volt-amperes For 120/240-volt, 3-wire system: Net Computed Load, 104,150 volt-amperes ÷ 240 volts = 434 amperes. Feeder Neutral: Lighting and Small Appliance Load 69,150 volt-amperes Range Load: 35,000 volt-amperes at 70% (see Section 220-22) 24,500 volt-amperes Computed Load (neutral) 93,650 volt-amperes 93,650 volt-amperes ÷ 240 volts = 390 amperes. Further Demand Factor (see Section 220-22): 200 amperes at 100% 200 amperes 190 amperes at 70% 133 amperes Net Computed Load (neutral) 333 amperes See Tables 310-16 through 310-31, Notes 8 and 10. Example No. 4(b). Optional Calculation for Multifamily Dwelling Multifamily dwelling equipped with electric cooking and space heating or air conditioning and having 40 dwelling units. Meters in two banks of 20 each plus house metering and individual subfeeders to each dwelling unit. Each dwelling unit is equipped with an electric range of 8-kW nameplate rating, four 1.5-kW separately controlled 240-volt electric space heaters, CHAPTER 9 - TABLES AND EXAMPLES 70-841 Example No. 4(b) (Continued) and a 2.5-kW 240-volt electric water heater. Assume range, space heater, and water heater kW ratings equivalent to kVA. A common laundry facility is available to all tenants [Section 210-52(f), Exception No. 1]. Area of each dwelling unit is 840 sq. ft. Computed Load for Each Dwelling Unit (Article 220): General Lighting Load: 840 sq. ft. at 3 volt-amperes per sq. ft 2520 volt-amperes Electric Range 8000 volt-amperes Electric Heat 6 kVA 6000 volt-amperes (or air conditioning if larger) Electric Water Heater 2500 volt-amperes Minimum Number of Branch Circuits Required for Each Dwelling Unit: General Lighting Load: 2520 volt-amperes ÷ 120 volts = 21 amperes or two 15-ampere 2-wire circuits or two 20-ampere 2-wire circuits. Small Appliance Loads: Two 2-wire circuits of No. 12 [see Section 220-4(b)]. Range circuit: 8000 volt-amperes X 80% ÷ 240 volts = 27 amperes on a circuit of three No. 10 conductors as permitted in Column C of Table 220-19. Space Heating 6000 volt-amperes ÷ 240 volts = 25 amperes No. of circuits (see Section 220-4). Minimum Size Subfeeder Required for Each Dwelling Unit (Section 215-2): Computed Load (Article 220): General Lighting Load 2520 volt-amperes Small Appliance Load, two 20-ampere circuits 3000 volt-amperes Total Computed Load 5520 volt-amperes (without range and space heating) Application of Demand Factor: 3000 volt-amperes at 100% 3000 volt-amperes 2520 volt-amperes at 35% 882 volt-amperes Net Computed Load 3882 volt-amperes (without range and space heating) Range Load 6400 volt-amperes Space Heating (Section 220-15) 6000 volt-amperes Water Heater 2500 volt-amperes Net Computed Load for individual dwelling unit 18,782 volt-amperes For 120/240-volt, 3-wire system Net Computed Load 18,782 volt-amperes ÷ 240 volts = 78 amperes Subfeeder Neutral (Section 220-22) Lighting and Small Appliance Load 3882 volt-amperes Range Load: 6400 volt-amperes at 70% (see Section 220-22) 4480 volt-amperes Space and Water Heating (no neutral) 240 volt 0 volt-amperes Net Computed Load (neutral) 8362 volt-amperes 8362 volt-amperes ÷ 240 volts = 35 amperes 70-842 NATIONAL ELECTRICAL CODE Example No. 4(b) (Continued) Minimum Size Feeder Required from Service Equipment to Meter Bank for 20 Dwelling Units: Total Computed Load: Lighting and Small Appliance Load 20 X 5520 110,400 volt-amperes Water and Space Heating Load 20 X 8500 170,000 volt-amperes Range Load 20 X 8000 volt-amperes 160,000 volt-amperes Net Computed Load (20 dwelling units) 440,400 volt-amperes Net Computed Load Using Optional Calculation (Table 220-32) 440,400 volt-amperes X .38 167,352 volt-amperes 167,352 volt-amperes ÷ 240 volts = 697 amperes Minimum Size Main Feeder Required (less house load) for 40 Dwelling Units: Total Computed Load: Lighting and Small Appliance Load 40 X 5520 220,800 volt-amperes Water and Space Heating 40 X 8500 340,000 volt-amperes Range Load 40 X 8000 volt-amperes 320,000 volt-amperes Net Computed Load (40 dwelling units) 880,800 volt-amperes Net Computed Load Using Optional Calculation (Table 220-32) 880,800 volt-amperes X .28 246,624 volt-amperes 246,624 volt-amperes ÷ 240 volts = 1028 amperes Feeder Neutral Load for Feeder from Service Equipment to Meter Bank for 20 Dwelling Units: Lighting and Small Appliance Load 20 X 5520 volt-amperes 110,400 volt-amperes First 3000 volt-amperes at 100% 3000 volt-amperes 107,400 volt-amperes at 35% 37,590 volt-amperes Subtotal 40,590 volt-amperes 20 Ranges = 35,000 volt-amperes at 70% 24,500 volt-amperes (See Table 220-19 and Section 220-22.) Total 65,090 volt-amperes 65,090 volt-amperes ÷ 240 volts = 271 amperes Further Demand Factor (Section 220-22) First 200 amperes at 100% 200 amperes Balance: 71 amperes at 70% 50 amperes Total 250 amperes Feeder Neutral Load of Main Feeder (less house load) for 40 Dwelling Units: Lighting and Small Appliance Load 40 X 5520 volt-amperes 220,800 volt-amperes First 3000 volt-amperes at 100% 3000 volt-amperes 120,000 volt-amperes -3000 volt-amperes = 117,000 volt-amperes at 35% 40,950 volt-amperes 220,800 volt-amperes - 120,000 volt-amperes = 100,800 volt-amperes at 25% 25,200 volt-amperes Net Computed Lighting and Small Appliance Load 69,150 volt-amperes 40 Ranges = 55,000 volt-amperes at 70% 38,500 volt-amperes (See Table 220-19 and Section 220-22) Total 107,650 volt-amperes 107,650 volt-amperes ÷ 240 volts = 449 amperes CHAPTER 9 - TABLES AND EXAMPLES 70-843 Example No. 4(b) (Continued) Further Demand Factor (Section 220-22) First 200 amperes at 100%. 200 amperes Balance: 249 amperes at 70% 174 amperes Total 374 amperes Example No. 5(a). Multifamily Dwelling Served at 208Y/120 Volts, Three Phase All conditions and calculations the same as for Multifamily Dwelling [Example No. 4(a)] served at 120/240 volts, single phase except as follows: Service to each dwelling unit shall be two phase legs and neutral. Minimum Number of Branch Circuits Required for Each Dwelling Unit (Section 220-4): Range Circuit: 8000 volt-amperes ÷ 208 volts = 38 amperes or a circuit of two No. 8 conductors and one No. 10 conductor as permitted by Section 220-22. Minimum Size Subfeeder Required for Each Dwelling Unit (Section 215-2): For 120/208-volt, 3-wire system (without ranges) Net Computed Load: 3882 volt-amperes ÷ 2 legs ÷ 120 volts/leg = 16.2 amperes For 120/208-volt, 3-wire system (with ranges) Net Computed Load: range, 8000 volt-amperes ÷ 208 volts = 38.5 amperes Total load: range plus lighting = 54.7 amperes Subfeeder neutral: range, 5600 volt-amperes ÷ 208 volts = 26.9 amperes Total load: range plus lighting = 43.1 amperes Minimum Size Feeders Required from Service Equipment to Meter Bank (For 20 Dwelling Units-10 with Ranges): For 208Y/120-volt, 3-phase, 4-wire system Ranges: Maximum number between any two phase legs = 4 2 X 4 = 8. Table 220-19 Demand = 23,000. volt-amperes. Per phase demand: 23,000 volt-amperes ÷ 2 = 11,500 volt-amperes Equivalent 3-phase load = 34,500 volt-amperes Net Computed Load, (total): 40,590 volt-amperes + 34,500 volt-amperes = 75,080 volt-amperes 75,080 volt-amperes ÷ (208)(1.732) = 208.4 amperes Feeder Neutral Size 40,590 volt-amperes + 34,500 volt-amperes at 70% = 64,700 volt- amperes Net Computed Neutral Load: 64,700 volt-amperes ÷ (208)(1.732) = 179.6 amperes Minimum Size Main Feeder (less house load) (For 40 Dwelling Units - 20 with Ranges): For 208Y/120-volt, 3-phase, 4-wire system Ranges: Maximum number between any two phase legs = 7 2 x 7 = 14. Table 220-19 Demand = 29,000 volt-amperes. Per phase demand: 29,000 ÷ 2 = 14,500 volt-amperes Equivalent 3-phase load = 43,500 volt-amperes Net Computed Load (total): 69,150 volt-amperes + 43,500 volt-amperes = 112,650 volt-amperes 112,650 volt-amperes ÷ (208)(1.732) = 312.7 amperes 70-844 NATIONAL ELECTRICAL CODE Example No. 5(a) (Continued) Main Feeder Neutral Size 69,150 volt-amperes + 43,500 volt-amperes at 70% = 99,600 volt-amperes 99,600 volt-amperes ÷ (208)(1.732) = 276.5 amperes Further Demand Factor (Section 220-22) 200 amperes at 100% 200.0 amperes 76.5 amperes at 70%. 53.6 amperes Net Computed Load 253.6 amperes Example No. 5(b). Optional Calculation for Multifamily Dwelling Served at 208Y/120 Volts, Three Phase All conditions and calculations the same as for Optional Calculation for Multifamily Dwelling [Example No. 4(b)] served at 120/240 volts, single phase except as follows: Service to each dwelling unit shall be two phase legs and neutral. Minimum Number of Branch Circuits Required for Each Dwelling Unit (Section 220-4): Range Circuit: 8000 volt-amperes at 80% ÷ 208 volts = 30.7 amperes or a circuit of two No. 8 conductors and one No. 10 conductor as permitted by Section 220-22. Space Heating: 6000 volt-amperes ÷ 208 volts = 28.8 amperes. Two 20-ampere, 2-pole circuits required, No. 12 conductor. Minimum Size Subfeeder Required for Each Dwelling Unit. Computed Load (120/208-volt, 3-wire circuit) Net Computed Load: 18,782 volt-amperes ÷ 208 volts = 90.3 amperes Net Computed Load: Lighting (line to neutral) 3882 volt-amperes ÷ 2 legs ÷ 120 volts/leg 16.2 amperes Line to line: 14,900 volt-amperes ÷ 208 volts 71.6 amperes Total load: 87.8 amperes Minimum Size Feeder Required for Service Equipment to Meter Bank (For 20 dwelling units): Net Computed Load: 167,352 volt-amperes ÷ (208)(1.732) = 464.9 amperes Feeder Neutral Load: 65,080 volt-amperes ÷ (208)(1.732) = 180.67 amperes Minimum Size Main Feeder Required (less house load) (For 40 dwelling units): Net Computed Load: 246,624 volt-amperes ÷ (208)(1.732) = 685.1 amperes Main Feeder Neutral Load: 107,650 volt-amperes ÷ (208)(1.732) = 298.8 amperes Further Demand Factor (Section 220-22) 200 amperes at 100% 200.0 amperes 98.8 amperes at 70% 69.2 amperes Net Computed Load 269.2 amperes CHAPTER 9 - TABLES AND EXAMPLES 70-845 Example No. 6. Maximum Demand for Range Loads Table 220-19, Column A applies to ranges not over 12 kW. The application of Note 1 to ranges over 12 kW (and not over 27 kW) and Note 2 to ranges over 83/4 kW (and not over 27 kW) is illustrated in the following examples: A. Ranges all the same rating (Table 220-19, Note 1). Assume 24 ranges, each rated 16 kW. From Column A, the maximum demand for 24 ranges of 12 kW rating is 39 kW. 16 kW exceeds 12 kW by 4. 5% X 4 = 20% (5% increase for each kW in excess of 12). 39 kW X 20% = 7.8 kW increase. 39 + 7.8 = 46.8 kW: value to be used in selection of feeders. I B. Ranges of unequal rating (Table 220-19, Note 2). Assume 5 ranges, each rated 11 kW. 2 ranges, each rated 12 kW. 20 ranges, each rated 13.5 kW. 3 ranges, each rated 18 kW. 5 X 12 = 60 use 12 kW for range rated less than 12. 2 X 12 = 24 20 X 13.5 = 270 3 X 18 = 54 30 408 kW 408 ÷ 30 = 13.6 kW (average to be used for computation). From Column A, the demand for 30 ranges. of 12 kW rating is 15 + 30 = 45 kW. 13.6 exceeds 12 by 1.6 (use 2). 5% X 2 = 10% (5% increase for each kW in excess of 12). 45 kW X 10% = 4.5 kW increase. 45 + 4.5 = 49.5 kW: value to be used in selection of feeders. Example No. 8. Motors, Conductors, Overload, and Short-Circuit and Ground-Fault Protection (See Sections 240-6, 430-6, 430-7, 430-22, 430-23, 430-24, 430-32, 430-34, 430-52, and 430-62 and Tables 430-150 and 430-152.) Determine the conductor size, the motor overload protection, the branch-circuit short-circuit and ground-fault protection and the feeder protection, for one 25-horsepower squirrel-cage induction motor (full voltage starting nameplate current 31.6 amperes, service factor 1.15, Code letter F), and two 30-horsepower wound-rotor induction motors (nameplate primary current 36.4 amperes, nameplate secondary current 65 amperes, 40°C rise), on a 460-volt, 3-phase, 60-Hertz supply. Conductor Loads The full-load current value used to determine the ampacity of conductors for the 25-horsepower motor is 34 amperes [Section 430-6(a) and Table 430-150]. 70-846 NATIONAL ELECTRICAL CODE Example No. 8 (Continued) A full-load current of 34 amperes X 1.25 = 42.5 amperes (Section 430-22). The fullload current value used to determine the ampacity of primary conductors for each 30-horsepower motor is 40 amperes [Section 430-6(a) and Table 430-150]. A fullload primary current of 40 amperes X 1.25 = 50 amperes (Section 430-22). A fullload secondary current of 65 amperes X 1.25 = 81.25 amperes [Section 430-23(a)]. The feeder ampacity will be 125 percent of 40 plus 40 plus 34, or 124 amperes (Section 430-24). Overload and Short-Circuit and Ground-Fault Protection Overload. Where protected by a separate overload device, the 25-horsepower I motor, with nameplate current of 31.6 amperes, shall have overload protection of not over 39.5 amperes [Sections 430-6(a) and 430-32(a)(1)]. Where protected by a separate overload device, the 30-horsepower motor, with nameplate current of 36.4 amperes, shall have overload protection of not over 45.5 amperes [Sections 430-6(a) and 430-32(a)(1)]. If the overload protection is not sufficient to start the motor or to carry the load, it shall be permitted to be increased according to Section 430-34. For a motor marked "thermally protected," overload protection is provided by the thermal protector [see Sections 430-7(a)(12) and 430-32(a)(2)]. Branch-Circuit Short-Circuit and Ground-Fault. The branch circuit of the 25-horsepower motor shall have branch-circuit short-circuit and ground-fault protection of not over 300 percent of a nontime-delay fuse (Table 430-152) or 3.00 X 34 = 102 amperes. The next smaller standard size fuse is 100 amperes (Section 240-6). Since a 100-ampere fuse is adequate to carry the load, Section 430-52(a), Exception No. 1. does not apply. If a time-delay fuse is to be used, see Section 430-52(a), Exception No. 2b. Where the 100-ampere fuse will not allow the motor to run, the value for a nontime-delay fuse shall be permitted to be increased to the next larger standard size, or 110 amperes. If these fuses are not sufficient to start the motor, the value for a nontime-delay fuse shall be permitted to be increased to 400 percent [See Section 430-52(a), Exception No. 2a.] Feeder Circuit. The maximum rating of the feeder short-circuit and ground-fault protection device is based on the sum of the largest branch-circuit protective device (100-ampere fuse) plus the sum of the full-load currents of the other motors, or 100 + 40 + 40 = 180 amperes. The nearest standard fuse that does not exceed this value is 175 amperes [Section 430-62(a)]. Example No. 9. Feeder Size Determination for Generator Field Control. feeder. Determining conductor ampacity for a group of six elevators on a single (See Sections 620-15, 620-13, 430-26, and 430-24 and Tables 620-15 and 430-150. Determine the conductor ampacity for a feeder supplying the six elevators. The system is generator field control. The ac drive motor horsepower rating of the largest MG set for one elevator is 40 horsepower, and the remaining elevators each have a 30-horsepower ac drive motor rating for their MG sets. Each controller draws 10 amperes to operate relays, power supplies, and the dooroperator. The line power supply is 460 volts, 3-phase, 60 Hz ac. The MG sets are rated continuous. CHAPTER 9 - TABLES AND EXAMPLES 70-847 Example No. 9 (Continued) Conductor ampacity is determined as follows: (a) Per Table 430-150, the full-load current for a 30-horsepower ac motor at 460 volts is 40 amps; for a 40-horsepower ac motor at 460 volts, 52 amps. (b) Per Section 430-24, Exception No. 1, determine the ampere rating for each motor used for other than continuous duty from Table 430-22(a), Exception. (c) Per Table 430-22(a), Exception, for intermittent duty using a continuous rated motor, the percentage of nameplate current rating to be used is 140%. (d) For the 30-horsepower ac drive motors, 1.4 X 40 amps = 56 amps. For the 40-horsepower ac drive motors, 1.4 X 52 amps = 73 amps. (e) Per Section 430-24, the total conductor ampacity is: 1.25 X largest motor current + the sum of the remaining motor currents = (1.25 X 73) + (5 X 56) = 371 amps. (f) Per Section 620-15 and Table 620-15, the conductor (feeder) ampacity shall be permitted to be reduced by the use of a demand factor. For six elevators, the demand factor is .79. The feeder motor ampacity is, therefore, .79 X 371 amps = 293 amps. (g) The total feeder ampacity is the sum of the motor diverse current and the controller (constant) current. I total = 293 + (6 X 10) = 353 amps. (h) This total ampacity shall be permitted to be used to select the wire size. Example No. 10. Determining Conductor Ampacity for a Group of Six Elevators on a Single Feeder Using Adjustable Speed Drive. (See Sections 620-14, 620-15, and 430-26 and Table 620-15.) Determine the conductor ampacity for a feeder supplying six identical elevators. The system is adjustable speed SCR dc drive. The transformers are external to the drive cabinet. Each drive has an ac nameplate rating of 204 amps. Each transformer is rated 85 kVA with a 300V secondary; efficiency is 90%. The ac line voltage is 460 volts, 3-phase, 60 Hz. Conductor ampacity is determined as follows: (a) Per 620-14(b), calculate the nameplate current rating of the transformer: I = 85 X 1000 = 119 amps J3 X 460 X 0.9 (b) Per Section 620-14(b), calculate the drive input current reflected to the transformer primary: I = 204 A X 300 V/460 V = 133 amps (c) Per Section 620-14(b), the larger current is 133 amps. (d) For six elevators, the total conductor ampacity is 6 X 133 amps = 798 amps. (e) Per Section 620-15 and Table 620-15, the conductor (feeder) ampacity shall be permitted to be reduced by the use of a demand factor. 70-848 NATIONAL ELECTRICAL CODE For six elevators, the demand factor is .79. The feeder ampacity is, therefore, .79 X 798 amperes = 630 amperes. (f) This ampacity shall be permitted to be used to select the wire size subject to Section 430-26. 70-849 Appendix A Extracts (See Section 90-3, Paragraph 4) A-500-3, FPN Classification of Gases, Chapter 3, Class No. 13 Vapors, and Dusts for Elec- II Materialstrical Equipment in Hazard- Dusts ous (Classified) Locations, NFPA 497M-1991 A-500-3, FPN Classification of Gases, Chapter 3, Class No. 14 Vapors, and Dusts for Elec- II Materialstrical Equipment in Hazard- Dusts ous (Classified) Locations, NFPA 497M-1991 A-514-2 Automotive and Marine Ser-