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Codeology 6

Lesson 6: Practical Guidelines for OCPD Ampere Rating Sizing /

QuestionAnswer
In addition to determining the proper OCPD ampere rating for an application, what criteria is/are important when selecting overcurrent devices? Select one: a. Interrupting rating b. Short-circuit current ratings c. Voltage rating d. All of the abov d. All of the above
In some cases, momentary high inrush currents during motor starting can reach as high as ? times the normal running current amperes during the first 1/2 cycle. Select one: a. 2 b. 4 c. 10 d. 20 d. 20
When an AC motor is started across the line, a high inrush current occurs. True
Most circuit breakers and fuses would “nuisance open” on motor startup if sized to provide motor and branch-circuit overload protection. As a result, motor branch circuits are permitted by NEC requirements to have two separate overcurrent protective devic Tue
Which of the following is typically true regarding motor overcurrent protection? I. Motor branch-circuit short-circuit and ground-fault protection is located at the beginning of a motor branch circuit in order to provide short-circuit and ground-fault c. Both I. and II.
Which NEC section provides the separate overload device rating or trip setting requirement for continuous-duty motors more than one horsepower? 430.32(A)(1)
A motor with a service factor number is designed to operate above its _____________ rating Horsepower
9.Separate motor and branch-circuit overload protection is sized based upon the ? a. Full load current based on motor horsepower in NEC Tables 430.247 to 430.250 b. maximum locked-rotor current c. motor nameplate full-load current d. start-up curr motor nameplate full-load current
10.It is necessary to select a separate overload protective device for a 25-horsepower continuous-duty motor with 32 amperes nameplate current rating and a marked 1.15 service factor. Table 430.250 shows 34 amperes for such a motor. What is the maximum tr c. 40 A Note: 32 × 1.25 = 40 A. See 430.32(A)(1). The correct answer is: 40 A
11. Using the conductor sizing guide in this lesson, what conductor ampacity is needed for a 10-horsepower, 230-volt single phase motor? c. 62.5 A Correct Note: Motor ampacity from Table 430.248: 50 A Minimum conductor ampacity calculated = 50 × 1.25 = 62.5 A using Conductor Ampacity Selection Guide 6, 7, 8. The correct answer is: 62.5 A
12.According to 430.32, if a continuous-duty motor nameplate does not have a 1.15 or greater service factor or temperature rise of 40°C or less, then a separate overload protection device must be set at no more than ? (assuming that this selection wil b. 115%
13.According to 430.32, if a continuous-duty motor nameplate does not have a 1.15 or greater service factor or temperature rise of 40°C or less, then a separate overload protection device must be set at no more than ? (assuming that this selection wil d.80 A or 90 A
14.Using 430.52 and Table 430.248, what is the maximum size dual-element fuse short-circuit and ground-fault protective device allowed for a 10-horsepower, 230-volt, single-phase motor, assuming the motor starts with this size? a. 50 A b. 70 A c. 8 d. 90 A Correct Note: 50 × 1.75 = 87.5 A 430.52(C)(1) Exception 1 allows rounding-up to next size standard fuse. 87.5 = 90 ampere fuse. The correct answer is: 90 A
15.Using Table 430.52, what is the maximum instantaneous trip circuit breaker setting allowed for the motor installation using a 460-volt, 25-horsepower, 3-phase motor marked with a 115% service factor and a nameplate current of 32 amperes based upon 430. 272 A Note: 34 × 800% = 272 A The circuit breaker in this question is an instantaneous trip only circuit breaker which does not have an overload sensing element. Do not confuse this with a thermal magnetic circuit breaker. This result is the setting of
16. Instantaneous trip circuit breakers are also referred to as motor circuit protectors (MCPs) and are intended only for motor branch circuit short-circuit and ground-fault protection. True False True
17.Overcurrent protection for transformers requires special considerations due to the magnetizing inrush current, which occurs on the ? when the transformer is energized. a.primary Correct b. secondary c. primary and secondary a.primary
18.Size the maximum primary and secondary overcurrent devices for a 100-kilovolt-amperes, 3-phase transformer, a 480-volt primary, and a 208/120 volts secondary (Only consider the transformer and not conductor protection or panelboard protection). a. d. 300 A (primary) / 350 A (secondary)
19.The purpose of overcurrent protection of capacitors is for ? a. delay sequence protection b. ground-fault protection c. overload protection d. short-circuit protection d. short-circuit protection
20.Overcurrent protection is required in each ungrounded conductor supplying a capacitor. The conductor ampacity shall not be less than ? of the rated current of the capacitor. a. 100% b. 125% c. 135%Correct d. 150% c. 135% The correct answer is: 460.8
Feeder conductors supplying several motors, or a motor(s) and other load(s), shall have an ampacity not less than the sum of ? of the full-load current rating of the highest rated motor, determined by 430.6(A), plus the sum of the full-load current ratings of all other motors determined by 430.6(A), plus 100% of the non-continuous non-motor load, plus 125% of the continuous non-motor load a. 100% b. 125% c. 300% d. 800% 125% The correct answer is: 430.24
Created by: Shawnt321
 

 



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