ADVANCED CALCULATIONS

Transcription

1 ADVANCED CALCULATIONS 101. Why is it permissible in some cases to fuse a #14 AWG motor conductor with a 60 amp breaker when normally a #14 AWG should only be fused at 15 amps? a) the motor can't start at 15 amps b) the motor is protected by an overload device c) the inspector said so d) a #14 AWG copper conductor can't be fused at 60 amps e) a and b 102. What is the efficiency of a 2 HP 208 V single phase motor? a) 88% b) 90% c) 54% d) 95% 103. What is the maximum size time delay fuse for a Design E, 30HP- 480 V 3-phase, squirrel- cage motor? a) 30 A b) 80 A c) 50 A d) 70 A 104. What is the minimum size TW copper feeder for a 3-phase 460Volt 10HP motor and three single-phase 115Volt 2HP motors? a) #8 b) #6 c) #4 d) # Size the THW feeder conductors for 1-3-phase 7.5HP 208V motor and 2-3-phase 208V 5HP motors. a) #8 b) #6 c) #4 d) #2

2 106. Size feeder inverse time OCD for the following motors: 1-10HP 460V 3-phase and 1-2HP 460V 3-phase. a) 30A b) 35A c) 40A d) 45A 107. Size branch circuit non-time delay fusing for a 50HP, 460 Volt, three-phase squirrel cage motor. a) 100A b) 150A c) 200A d) 250A 108. Select minimum size square junction box for 2-#12AWG THHN with an equipment ground; 2-#14AWG THW with an equipment ground and terminating on a single pole switch; 2-#6AWG THHN passing through the box; and finally 2 clamps. a) 4 x 1 1/4 b) 4 11/16 x 1 1/2 c) 4 11/16 x 1 1/4 d) 4 x 1 1/ What minimum size box is needed for ten #14 AWG TW conductors, no grounds? a) 4 x 1 1/4 square b) 4 x 1 1/2 square c) 4 11/16 x 1 1/4 d) 4 11/16 x 1 ½ 110. Size minimum square box for U-Pull entering and leaving through a 4" Rigid Metal Conduit. a) 16" x 16 b) 24" x 24 c) 12" x 12 d) 32" x 32

3 111. A 24" nipple may be filled to what cross sectional capacity? a) 53% b) 40% c) 60% d) 75% 112. What size Schedule 40 PVC conduit is required for 8- #12 TW, 12- #14 THW, 8- #10 THHN, and 6- #6 THWN conductors? a) 1.5 b) 2 c) 2.5" d) What is the internal diameter of a 3" rigid conduit? a) 3.356" b) 3.042" c) 3.090" d) 3.000" 114. What is the voltage drop for a 220 Volt system supplying power to a 1000Watt load, 500 feet from the last fuse box, using #10THWN stranded, coated copper conductors? a) 5.14Volts b) 5.26 Volts c) 5.65 Volts d) 5.86 Volts 115. What is the total percentage of voltage drop on a 240 Volt service supplying a subpanel 1500 feet away that feeds a well pump 600 more feet from there, when the sub-panel feeder drops 7.9 volts and the well pump branch circuit drops 5.8volts? a) 4.20% b) 5.70% c) 6.30% d) 14.0%

4 116. What is the demand load on a single dwelling service for a 12KW Electric Range? a) 12 KW b) 8 3/4 KW c) 8 KW d) 12.6 KW 117. Calculate the service demand load for a 12KW household oven and a 4KWcounter-top cooking unit. a) 9.6 KW b) 8 KW c) 16 KW d) 11.2 KW 118. What is the combined demand load in KW, for 1-14KW range, and 1-12KW pizza oven in a bar downtown? a) b) c) d) What is the minimum service demand in a motel restaurant kitchen that contains a 14KW range; a 16KW oven; a 5KW dishwasher; a 5KW disposal; and a 1KW trash compactor? a) 41 KW b) 20 KW c) 25 KW d) 30 KW 120. What is the total range load for Mrs. Smith's Home Economics Class 3-12KW ranges? a) 12 KW b) 14 KW c) 16 KW d) 24 KW

5 121. A 3-phase 4-wire 208Volt system powers twenty 12KW ranges and nine 8.75KW ranges in an apartment complex. What is the range load demand on the service? a) 24 KW b) 30 KW c) 35 KW d) 53 KW 122. The net calculated load for a 1500sq.ft. home with a 12KW range and a 5.5KW clothes dryer is VA? a) 18,600VA b) 9,000VA c) 12,000VA d) 4,000VAA 123. Now add to problem 122. one 6A Volt A/C unit; one 12A - 115Volt room A/C unit; one 8A Volt disposal; and one-10a - 120Volt dishwasher. Calculate the size of the service. a) 80 A b) 100 A c) 110 A d) 125 A 124. In a 40 unit apartment house, each unit is provided with a built-in dishwasher and disposal with a combined nameplate load of 3KW. What is the demand on the service for these extras? a) 90 KW b) 100 KW c) 120 KW d) 140 KW 125. The same apartment house in problem 124: Each unit has a 12KW range on the single phase 240/120Volt service. What is the combined neutral load on these ranges? a) 270 A b) 480 A c) 160 A d) 190 A

6 126. What is the minimum KW load used for calculating a range in an apartment building that is supplied by a three-phase AC service? a) 18 b) 12 c) 8 d) 1 ¾ 127. A mobile home park has 50 slots, each expecting 16KVA double-wides. What would the service demand load be? a) 150 KVA b) 800 KVA c) 1640 KVA d) 184 KVA 128. An RV park has 100 slots. 50 have 50 amp receptacles; 30 have 20 and 30 amp receptacles; and the remaining 20 are tent sites with 20 amp outlets. What is the demand on the service? a) 123 KVA b) 246 KVA c) 268 KVA d) 494 KVA 129. When installing an electric sign on the top of a downtown building, which of the following are true? Pick the best answer. a) The power supply may be located inside the building's attic. b) The thermal ballast shall be listed as thermally protected. c) A 3ft x 2ft access door must be provided d) all of the above 130. A jeweler needs to remodel his 30ft by 45ft ground floor office space to catch the attention of pedestrians who pass by his entrance. He also needs 40ft of show window lighting and, since it's very hot, a 230V single-phase 2HP A/C. What will the service load on his 230V/115V feeder be? a) 64.90A b) 82.84A c) 87.66A d) 89.88A

7 Answers 101. e), 430 Motors Read whole section 102 c) eff. = Output/input; 1HP = 746 watts; FLC Table d), Table ; Table b) Start at Fig ; Draw out the 3-phase diagram and balance the load 105. c) (24.2 x 1.25) =63.5 Motor & Ampacity tables 106. b) Fig ; Motor Tables; ; c) Table ; Table ; b) Table (A)-(B) 109. b) Table (A) 110. b) Table (A)(2) 111. c) Chapter 9; note a) Chapter. 9; Tables c) Chapter. 9; Table c) Chapter 9; Table 8; VD = (2 x 12.9Copper x 500ft x 4.54A)/10380 = b) (7.9V + 5.8V)/240V (don t make it harder than it is) 116. c), Table d) Table a)table note d) b) Table note c) Table ;

8 122. a) Annex D Examples 123. c) Annex D Examples 124. a) c) (B) 126. b) note d) ; Table c) ; Table d) (E) 130. a) Article ft. x 45ft. = 1350sq.ft. x 3VA x1.25 = 5062VA General Lighting load then the show window lighting is 200VA per foot = 200 x 40 = 8000VA; the A/C will be on all day so that s another 2 x 746VA x 1.25 = 1865VA adds up to 14927VA/230V = 64.90A