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Motor Installation By Bill Lee Article 430

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NF 15HP NF 25HP NF 30HP NF 50HP NF 75HP D.E.T.D. Fuse Feeder O.C. Feeder Conductors N.T.D IV. Time D.E.T.D N.T.D IV. Time Brach Circuit O.L All Motors 460V FLA 20A 40 Temp Rise FLA 30A S.F FLA 38A FLA 63A 40 Temp Rise FLA 93A S.F. 1.10

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Motor Calculations Article requires that Feeder Overcurrent device be sized based on the largest overcurrent in the group (based of Feeder % multiplier). This is to be added to the Full-Load Currents of all other motor supplied by that feeder. This code section does not allow for the next available overcurrent device as permitted for individual overcurrent devices. Calculation as follows…

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Feeder Calculations continued… Largest motor has FLC of 96A… 96A x 175% (Feeder Type) = 168A 168A is not a standard size code permits 175A overcurrent device. 175A + 21A + 34A + 40A + 65A = 335A Feeder must be sized to next lower O.C. Answer 300A

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Feeder Conductor Calculation… Article requires that all feeder conductors be sized at not less than the sum total of all motor FLC plus the largest motor FLC at 125%... (Largest Motor) 96A x 125% = 120A 120A + 21A + 34A + 40A + 65A = 280A Table requires… 300kcmil cu.

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Individual Brach Circuit Overcurrent Per Article overcurrent is sized… (15HP) 21A x 300% = 63A…70A (25HP) 34A x 250% = 85A…90A (30HP) 40A x 175% = 70A…70A (50HP) 65A x 300% = 195A…200A (75HP) 96A x 250% = 240A…250A

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Brach Circuit Conductors Article requires that all conductors be sized at not less than 125% of the FLC of the Motor. Article (c) (4) allows motors (types B, C and D) to use the 75 degree C ampacities of table Calculations will be as follows…

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Branch Circuit Conductors continued… 21A x 125% = 26.25A…#10 cu 34A x 125% = 42.5A…#8 cu 40A x 125% = 50A…#8 cu 65A x 125% = 81.25A…#4 cu 96A x 125% = 120A…#1 cu

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Branch Circuit Disconnects Article (A) requires that disconnects be sized at no less that 115% of the FLC of the Motor supplied… 21A x 115% = 24.15A…30A 34A x 115% = 39.1A…60A 40A x 115% = 46A…60A 65A x 115% = 74.75A…100A 96A x 115% = 110.4A…200A

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Overload Protection Article requires overload protection to be sized based on the FLA of the motor protected… 20A x 125% = 25A…25A 30A x 125% = 37.5A…37.5A 38A x 115% = 43.7A…43.7A 63A x 125% = 78.75A…78.75A 93A x 115% = A106.95A

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15HP 25HP 30HP 50HP 75HP All Motors 460V 300A 300kcmil cu 70A 90A 70A 200A 250A #10 Cu # 8cu #4 cu #1 cu 30A 60A 100A 200A 25A 67.5A 43.7A 78.75A A

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