Chapter 12 Branch Circuits and Feeders 181 Copyright Goodheart-Willcox Co., Inc. Show-window = 40′ × 200 VA lighting load = 8000 VA Sign lighting n load = 1200 VA Recepta t ac le load = 60 × 180 VA = 10,800 VA H He ating/air- = 50,000 VA conditioning load Motor load = 4.9 A × 240 0 V = 1176 VA A The total lighting load is the co c om bination of the three separate lighting loads. d Total lighting load = = 14,400 VA + 8000 VA + 1200 VA = 23,600 VA The motor load d and lighting loads are continu- ous, so the con o nd uctors must supply 125% of the full-load cur u rr ent: Total lighting li load = 23,600 VA × 1.25 = 29,500 VA Motor load = 1176 VA × 1.25 = 1470 VA All loads are added to determine the he total load: Total load = 29,500 VA + 10,800 0, VA + 50,000 VA + + 1 14 70 VA = 91,770 VA A The total current can be e calculated: I = I P _ E = 91,770 VA V A _____ _ 240 V V V = 382 2 A Using Tab Ta bl e 310.15(B)(16), 500 kcmil conductors will be e suffi fficient. (Continued) The neutral feeder conductor n is sized for the 120-volt loads (lighting h and receptacles) only. Neutral = Lighting g load + feeder load Re ec eptacle load = 2 29 ,500 VA + 10,800 VA = 40,300 VA The current can be calculated: I = I _P E = 40,3___AV0__ 00 _ 240 4 V = 168 A A 2/0 AWG W G copper conductor shou ul d be used for the neutral e feeder conductor. SAMPLE PROBLEM 12-13 P Pr oblem: A two-story office building (80′ ffi ffi × 80′) is supplied with 120/208-volt 2 service. Sev- eral loads are supplied: 75-kVA air-conditioni n in g unit 85-kVA heating uniti t 200 duplex receptacles p 50 linear feet of o f show window 30 exterior lig gh t fixtures (175 VA each) fi 3 blower mo m ot ors (3/4-hp, 208-volt) Copper THW W conductors are used as fee ed ers. What size should sh the current-carrying co c on duc- tors be? Solution: n First, all loads must be computed. co The hea at ing unit and air-conditioning n unit will not be e used at the same time, so on nl y the larger load is needed. The 3/4-hp, 208 8- volt motors draw w 3.5 amps, as shown in Table 430.250. The h e actual motor voltage is 208 0 V × 1.732 (or 360 36 volts) because the service is i three-phase. (Continued)