180 Modern Commercial Wiring Copyright Goodheart-Willcox Co., Inc. 5. Compute receptacle outlets as follows: • Receptacles as 180 VA each (Section 220.14(I)) • Multioutlet assemblies at 180 VA per each 5′ portion (Section 220.14(H)(1)) • Show windows at either of the following (Section 220.14(G)): (1) The unit load per outlet as required in other provisions of Section 220.14 (2) At 200 VA per 300 mm (1 foot) of show window • Heavy-duty lamp holders at 600 VA each. (Section 220.14(E)) • Others as outlined in Section 220.14. 6. Apply any of the demand factors as shown in Table 220.44 for receptacle loads and Table 220.56 for kitchen equipment loads. 7. Add the sign lighting load (1200 VA minimum). (Section 220.14(F)) 8. Compute the motor loads using the appropriate tables in Article 430. 9. Increase largest motor load based on full- load current by 25%. (Section 430.24) 10. Size the service and service conductors. Compute by dividing the total load by the line voltage. Conductor size is selected from Table 310.15(B)(16). 11. Using the guideline given in Section 250.24(C), size the grounded service conductor. Be sure the grounded service conductor is not smaller than the grounding electrode conductor as given in Table 250.66. 12. Provided there is no discharge lighting, the neutral load—if over 200 amperes—can be derated by 70%. Refer to Section 220.61. 12.6 Sample Problems The following examples represent a small sam- pling of situations requiring computations to determine correct sizing of equipment, con- ductors, overcurrent protection, and other load demands encountered in commercial wiring. The main purpose is to introduce the concept and give the reader a general feel for the over- all procedure. Numerous other factors, such as wiring methods, routing, distances, and voltage drop (to name a few), have been purposefully ignored here for the sake of simplicity. Still, by reviewing and understanding these examples and the step-by-step methodology, the com- mercial electrician, designer, engineer, and stu- dent will be better equipped to move on to the “real” calculations required in practical design situations. The following problems illustrate load cal- culation and feeder sizing for commercial structures: • Small retail store—Sample Problem 12-12. • Offi building—Sample fice Problem 12-13. • Restaurant—Sample Problem 12-14. • Hotel—Sample Problem 12-15. SAMPLE PROBLEM 12-12 Pro ob lem: A small retail store e is being con- str t ru cted. Its power supply is single-phase, 1 12 0/240-volt. The store is 80′ × 60′ and has sev- eral loads: 50-kVA heating equipm me nt 25-kVA air-conditioni n in g unit 1/2-hp, 240-volt ve en tilating unit 60 duplex receptacles pt 40 linear feet of o show-window lighting 1.2-kVA outdoor d sign lighting Copper THW W conductors are used as feeders. d What size should sh the current-carrying feeders ee be? Solution: n : First, all the loads must be b com- puted. The T heating unit and air-conditioning nd unit wi w il l not be used at the same tim me , so only the larger a load is needed. The 1/2-hp, -h 240-volt mot o to r draws a current of 4.9 amps p s, as shown in Tab a bl e 430.248. General lighting = 80′ × × 60′ × 3 VA/ft2 load = 14,400 4, VA (Continued)