| Question | Answer |
| 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 |
