cee496-problemset3sols

cee496-problemset3sols - CEE 496 — ELECTRICAL BUILDING...

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Unformatted text preview: CEE 496 — ELECTRICAL BUILDING SYSTEMS SOLUTION SET MARCH 29, 2005 PROBLEM SET #3 A new pump is being installed which will be fed from an existing motor control center with a spare motor starter which is capable of being locked in the open position. The pump will be installed in a location which is visible from the motor control center and 55 feet away. The pump is driven by a 460 volt, 3-phase, 50HP, NEMA design B, code letter H, squirrel cage induction motor with a 1.15 service factor and, name plate rated full load current of 72 amperes. The ambient temperature where the pump is located is 86° F. Provide the following information about the branch circuit serving the new pump: 1. What is the minimum branch circuit conductor size? Determine the full load current (NEC Table 430-250) IFull load current : 65A Satisfy integrity of terminals: IConducto, = 1.25 (65A) = 81.25A < 100A use 60°C column Select #3AWG, amacit = 85 No derating necessary for temperature or # of current carrying conductors. 2. What is the maximum NEC standard size short circuit protection assuming a dual element time-delay fuse? Per Table 430-52: IFuse s 1.75 (65A) = 113.75A/ Select 125A Fuse Note: Per Exception No. 2(b), the fuse size could be increased if the motor will not start, but shall not exceed 225 percent of the full load current. - 3. What is the maximum overload protection? Per Section 430-32(A)(1): i0L s 1.25 (72A) = 4. How many disconnects are required by the NEC for this installation and where are they located? What is the minimum disconnect rating in amperes allowed by the NEC? Per Section 430-102(A) & (B): 'One disconnect is required and should be located within the ‘ MCC ‘ Per Section 430-109(A)(1) and 430-110(A): IDisconnet 2 1.15(65A) = ' 74.75A Select the next standard switch size: 100A Note: The disconnect must also have a horsepower rating 2 the motor horsepower. - 5. What is the minimum EMT raceway trade size that can be used? From Table 5, Chapter 9 _ Area of #3AWG, THHN 0.0973sq_ in Area of #BAWG, THHN = 0.0507sq_ in (Ground) Total conductor area = 3 (0.0973sq, in) + 0.0507sq_ m = IO.34265q_ m From Table 4, Chapter 9 Area of EMT conduit at 40% fill 2 0.34268”, Select 1” EMT Area = 0.3463_m. a 40% fill 6. Provide a one-line diagram showing all components and sizes necessary for the electrician to connect the pump. ' ...
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cee496-problemset3sols - CEE 496 — ELECTRICAL BUILDING...

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