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JOURNEYMAN ELECTRICIAN’S EXAM WORKBOOK

Ungrounded Conductors 310.15(B)(7): 200 A × 0.83 = 166 A Table 310.15(B)(16): 120 V THW 75°C Cu conductors = 2/0 Grounded Conductor Table 250.102(C)(1):2/0 or 3/0 Cu = #4 grounded conductor = #4 Cu Article 310.15(B)(7) permits the grounded conductor to be smaller than the ungrounded conductor. The AHJ may permit a dropping of two trade sizes or may require a load calculation to reduce the neutral size. 63. An apartment building has a 120/208 V, 3φ, 4-wire service with a 100 A, 120/208 V, 1φ feeder of THW Cu to each apartment. What are the sizes for the ungrounded and grounded conductor to each apartment? Ungrounded Conductor 310.15(B)(7): 100 A × 0.83 = 83 Α Ungrounded Conductor = #4 Grounded Conductor 310.15(B)(5)(b): No reduction permitted for the neutral Grounded Conductor = #4 Cu Article 310.15(B)(5)(b) states that the neutral conductor, when using two phases of a 3φ, 4-wire, wye system, carries approximately the same current as the other conductors. 64. The GEC in Problem 62 is an underground water pipe. What size Cu GEC is required? 250.66(A): Not required to be larger than # 6 Cu GEC = #6 Cu The GEC is based on the largest service entrance conductor per Table 250.66. 65. The grounding electrode in Problem 62 is a concrete-encased electrode. What size Cu GEC is required? 250.52(A)(3);250.66(B): Not required to be larger than #4 Cu GEC = #4 Cu

SERVICE LOAD CALCULATIONS (OPTIONAL CALCULATION–220.82) Article 220 permits two methods for computing service entrance loads for a dwelling unit. Part I is general information. Parts III and IV are used for the standard and optional methods for calculating service entrance loads

and conductor sizes. The Optional Calculation is a quick and simple method to use. It is the most common method used for computing service entrance loads for dwellings, although the loads may calculate slightly higher than with the Standard Calculation. See 220.82. Informative Annex D of the NEC® shows examples for each method. Examples: Optional Calculation

Use for Problems 66 through 74. A dwelling unit has a 50′ × 42′ floor area with a 20 sq ft attached garage. The dwelling unit has a 3 kW range, 4.5 kW hot water heater, 5 kW electric dryer, ¹⁄₃ HP food waste disposal, 1.2 kW dishwasher, and a 40 A, 240 V heat pump with 10 kW of supplemental heat. No system interlock. The service is 120/240 V, 1φ. 66. What is the general lighting load (Optional Calculation)? 220.82(B)(1): 50′ × 42′ × 3 VA = 6300 VA General Lighting Load = 6300 VA Allow 3 VA per sq ft for general lighting and general-use receptacles per 220.82(B)(1). The floor area is computed from the outside dimensions of the dwelling. For dwelling units, the computed floor area does not include open porches, garages, or unused or unfinished spaces not adaptable for future use per 220.12. 67. How many 15 A, 2-wire circuits are required for general lighting (Optional Calculation)? P E 6300 I= = 52.5 120 52.5 = 3.5 (round to 4) 15 Twoo-wire Circuits = 4 I=

All general-use receptacle outlets of 20 A or less in dwelling units (except for small appliance and laundry outlets) shall be considered for general illumination. No additional load calculations shall be required for such outlets per 220.14(J). 68. What is the calculated load for the ungrounded (hot) conductors (Optional Calculation)? See 220.82 and Annex D, Example D2(c). 220.82(B)(1): General Lighting:

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Journeyman Electrician's Exam Workbook Based on the 2017 NEC®  

Journeyman Electrician’s Exam Workbook Based on the 2017 NEC® is designed to help applicants prepare for the journeyman electrician’s state...

Journeyman Electrician's Exam Workbook Based on the 2017 NEC®  

Journeyman Electrician’s Exam Workbook Based on the 2017 NEC® is designed to help applicants prepare for the journeyman electrician’s state...

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