CSP 6 Lesson 1, CSP 6 Lesson 2, CSP6 Lesson 3, CSP6 Lesson 4, CSP6 Lesson 5, CSP6 Lesson 6, CSP6 Lesson 7
Where the value for a branch-circuit short-circuit and ground-fault protective device determined by Table 430.52 for a dual-element fuse or inverse time circuit breaker does not correspond to a standard ampere rating, a ? ampere rating or setting that does not exceed the next higher standard ampere rating shall be permitted.
higher 430.52(C)(1)
For a 7% impedance transformer over 1,000 volts in a supervised location and without coordinated thermal overload protection, a primary fuse could be sized up to ? (or the next commercially available ampere rating) without secondary protection.
250%
Determine the maximum standard size rating of the motor branch-circuit short-circuit and ground-fault protective device for a five-horsepower, 208-volt, 3-phase, squirrel cage induction motor using dual-element fuses when starting current of the motor is not an issue.
30 A 240.6(A)
Determine the maximum rating of the motor branch-circuit short-circuit and ground-fault protective device when starting current is a problem for a three-horsepower, 230-volt, single-phase capacitor motor using time-delay fuses.
35 A 240.6(A) Table 430.248 = 17 amperes430.52 (C)(1) Ex. No. 2 = 225%17 A × 2.25 = 38.3 A (next smaller standard size is the largest permitted)240.6(A) = 35 ampere OCPD is next lowest standard size
The type of motor disconnecting means is covered by NEC ? .
430.109
Overcurrent protection for panelboards supplied through a transformer 1000 volts, nominal, or less is specifically addressed in ? .
Article 408, Part III 408.36(B)
Which one of the following statements is NOT correct per the Article 100 definition of branch-circuit overcurrent protective device?
Branch-circuit overcurrent protective devices must be listed in combination with the specific devices they are intended to protect.
A 600-volt AC fuse or circuit breaker is considered to have a 600-volt DC rating, even if it is not marked with a DC voltage rating.
False
A mini-circuit breaker (UL 1077 supplemental protector) or supplemental fuses are suitable for use as motor branch-circuit short-circuit and ground-fault protection.
False
A motor is located 100 feet from the motor control center that houses the motor branch-circuit disconnect. An instantaneous-trip circuit breaker can be used for the "within-sight" motor disconnect. This would entail the instantaneous-trip circuit breaker being installed alone in a separate enclosure.
False
Which of the following characteristics of motor branch circuits make them unique branch circuits?
I. Circuit components such as starters, overload heaters, and contactors that have low short-circuit withstands or SCCRs II. Higher probability to incur short-circuit conditions III. The desire for various levels of functionality, such as remote push-button control and automatic control IV. The harsh demand of motor loads, such as inrush and locked rotor currents V. The multitude of potential devices that may be used in motor circuits
Each motor used in a continuous-duty application and rated more than one horsepower is required to be protected against overload. A separate overload device that is responsive to motor current is one of four options permitted to protect against overload.
True
Separate motor overload protection shall be based upon the motor nameplate ? rating.
current 430.6(A)(2)
NEC ? covers the requirements for the motor controller disconnecting means.
430.102(A)
Overload protection for continuous-duty motors one horsepower or less, automatically started, is covered by NEC ? .
430.32(B)
MCPs are recognized devices (not listed) and are permitted by ? to provide motor branch-circuit short-circuit and ground-fault protection, if used as part of a listed combination with a starter.
430.52(C)(3)
Which NEC article applies to electric motor-driven air-conditioning and refrigerating equipment and to the branch circuits and controllers for such equipment?
440
What section of Article 450 details the basic ampere rating sizing requirements for overcurrent protection of transformers?
450.3
For a part-winding connected motor, the ampacity of the branch-circuit conductors on the line side of the controller shall not be less than 125% of the motor full-load current as determined by 430.6(A)(1). The ampacity of the conductors between the controller and the motor shall not be less than ? of the motor full-load current rating as determined by 430.6(A)(1).
62.5% 430.22(D)
Article 450 covers the installation of transformers dedicated to supplying power to a fire pump installation as modified by Article ? .
695 450.1
A 3-phase, 750-kVA, 5.75% impedance transformer in an unsupervised location, with a primary voltage of 4,160 volts and a secondary voltage of 480 volts, could have a primary circuit breaker sized at a maximum of ? .
700 A
The internal parts of fuses require maintenance.
False
The maximum rating or setting of overcurrent protection for transformers under 1,000 volts per 450.3 is different for circuit breakers compared to fuses.
False
The voltage rating of the OCPD must be equal to but never greater than the circuit voltage.
False
When increased sizing of the overcurrent protective device is utilized on the secondary side of a transformer, overcurrent protection on the primary side, sized closer to the load, is typically required.
False
A 480/277-volt, 3-pole circuit breaker can be applied on a 480-volt corner-grounded delta.
False 240.85
Part ? of Article 430 covers the requirements for the motor disconnecting means.
IX
The two tables of concern for transformer protection are Table 450.3(A) for transformers over 1,000 volts, nominal and Table 450.3(B) for transformers 1,000 volts or less.
True
When fault current is within the current-limiting range of a current-limiting OCPD, the thermal energy and magnetic (mechanical) forces can be greatly reduced. The levels of both thermal energy and magnetic forces are proportional to the square of the fault current that flows.
True
When the conductor ampacity does not correspond to a standard OCPD ampere rating, the next standard OCPD ampere rating is permitted if that rating does not exceed 800 amperes, and if the conductors are not supplying a circuit with more than one receptacle for cord-and-plug portable loads.
True
For a motor branch circuit where the motor is within 50 feet and within sight of the branch-circuit disconnect, branch-circuit fuses (if properly sized) in conjunction with a UL 98 disconnect can be suitable for these four functions: motor branch-circuit disconnect, motor branch-circuit short-circuit and ground-fault protection, motor controller, and within-sight motor disconnect.
True
A ? overcurrent protective device is one that clears a fault current in one half cycle or less and reduces the amount of fault current let-through.
current-limiting
For the purposes of the application of Table 450.3(A), a "supervised location" is a location where conditions of maintenance and supervision ensure that only qualified persons monitor and service the transformer installation.
True
For transformers 1,000 volts or less, the secondary overcurrent protection device can be split into up to six devices, provided the sum of the ampere ratings does not exceed that permitted if it were only a single secondary overcurrent protective device and the conditions of Article 240 and Article 408 are satisfied.
True
Generally, a fully-loaded 3-phase motor protected by three properly sized overload protective devices will be protected against single-phasing.
True
Listed or labeled equipment must be installed and used in accordance with any instructions included in the listing or labeling.
True
Molded case circuit breakers (MCCBs) are the most prevalent circuit breakers in use for 15 amperes to 2,500 amperes.
True
Overcurrent protection for motor circuits is segmented into which of the following?
a. Motor branch-circuit short-circuit and ground-fault protection c. Motor and branch-circuit overload protection
Molded case circuit breakers, insulated case circuit breakers, and low-voltage power circuit breakers are ? .
branch-circuit overcurrent protective devices
Size the overcurrent protective device needed to feed one 25-horsepower, 480-volt, 3-phase motor-compressor with a rated load current of 42 amperes and a branch-circuit selection current (BCSC) of 45 amperes when starting current is not a problem.
Use BCSC per 440.22(A) for OCPD size. OCPD ampacity = BCSC × 175% = 45 × 1.75 = 78.75 A Time-delay fuses or inverse-time circuit breakers must be rated no more than 70 amperes, which is the next smaller standard size per 240.6(A).
Part ? of Article 430 covers the requirements for motor controllers.
VII
The values given in Table 430.247, Table 430.248, Table 430.249, and Table 430.250 are generally used to determine which of the following for motor branch circuits?
a. Ampacity of conductors b. Branch-circuit short-circuit and ground-fault protection 430.6(A)(1)
A 3-phase, 750-kVA, 5.75% impedance transformer in an unsupervised location, with a primary voltage of 4,160 volts and a secondary voltage of 480 volts, could have a maximum primary fuse size of ? .
350 A
NEC ? covers interrupting rating requirements for equipment.
110.9
Fault current ? the normal conducting path.
flows outside
Fuses and circuit breakers are intended to protect conductors and equipment from the effects of potentially harmful ? .
overcurrents
Overcurrent protection for motor control circuits that protect control circuit transformers where the control circuit transformer primary is rated less than 2 amperes shall be permitted in the primary circuit where an overcurrent device is rated or set at not more than ? of the rated primary current.
500% 430.72(C)(4)
A 600-volt or less transformer equipped with coordinated thermal overload protection by the manufacturer and arranged to interrupt the primary current shall be permitted to have primary overcurrent protection rated or set at a current value that is not more than ? times the rated current of the transformer for transformers having not more than 6% impedance and not more than ? times the rated current of the transformer for transformers having more than 6% but not more than 10% impedance.
6 / 4
The motor branch-circuit short-circuit and ground-fault protective device shall be capable of carrying the starting current of the motor.
True 430.52(B)
A 3-phase, 750-kVA, 5.75% impedance transformer in an unsupervised location, with a primary voltage of 4,160 volts and a secondary voltage of 480 volts, would have a secondary circuit breaker sized at a maximum of ? .
1,200 A
The minimum ampacity for branch-circuit conductors supplying a 75-horsepower, 3-phase, induction-type squirrel cage motor that operates at 460 volts is ? .
120 A
Identify the NEC section where the following provision is located: A circuit breaker is used on a circuit having an available fault current higher than its marked interrupting rating by being connected on the load side of an acceptable overcurrent protective device having a higher rating. In this section, the circuit breaker shall meet the requirements specified in (A) or (B), and (C).
240.86
A horsepower-rated switch or circuit breaker is permitted as both the motor controller and disconnecting means in accordance with NEC ? .
430.111
The requirements for motor-circuit overcurrent protection for motors over 1,000 volts are covered in what section of Article 430?
430.225
A disconnecting means "in sight from the motor" is intended and used only as an emergency disconnecting means.
False Note: A disconnecting means "in sight from the motor" is used for isolating the motor circuit for maintenance and serves as an emergency disconnecting means.
Motor controllers serve as the motor ON/OFF function.
True
Overcurrent protective devices on a transformer primary may require increased sizing due to the magnetizing inrush current.
True
Magnetic motor starters listed to UL 508 are suitable for use ? .
b. as motor controllers c. as motor overload protection
A separate motor overload device for a continuous-duty motor more than one horsepower with a 1.15 service factor must be selected to trip or be rated at no more than ? of the motor nameplate full-load current rating. Assume the motor starts and runs continuously without nuisance tripping for this selection.
125%
Conductors that supply a single motor used in a continuous-duty application shall have an ampacity of not less than ? of the motor full-load current rating, as determined by 430.6(A)(1), or not less than specified in 430.22(A) through (G).
125% 430.22
The scope of Article 450 indicates that this article covers the installation of all transformers. There are ? exceptions that modify this Article 450 scope statement.
8
Only standard ampere rated fuses and circuit breakers found in 240.6 are permitted to be used in services, feeders, and branch circuits.
False Note: NEC 240.6(A) permits the use of nonstandard ampere ratings.
Primary inrush current characteristics can vary by transformer design.
True
A motor switch listed to UL 508 can be used as the motor branch-circuit disconnect.
False
Devices are permitted to only perform one motor circuit function.
False
For motor branch-circuit applications, the motor branch-circuit short-circuit and ground-fault protective device can be located anywhere on the motor branch circuit since fault currents stay within the normal conducting path.
False
NEC 240.10 permits a supplementary fuse to be used where a branch-circuit OCPD is required.
False
For transformers covered by the scope of Article 450, the nameplate must provide which of the following that are vital information for calculating the available fault current on the transformer secondary?
I. Impedance of transformers 25 kVA and larger II. kVA III. Primary and secondary voltage
Overload current is confined to the normal conductive path provided by the conductors, circuit devices, and loads of the distribution system.
True
Section 110.3 provides criteria and considerations for the evaluation of equipment and recognizes listing or labeling as a means of establishing suitability.
True
Table 450.3(A) provides provisions for both "any location" and "supervised locations only."
True
Since the 1971 edition of the NEC, 3-phase motors only need two phases protected with properly sized overload protection.
False
Supplementary overcurrent protective devices are permitted to be used as a substitute for a branch-circuit OCPD or where a branch-circuit OCPD is required (per 240.10).
False
Branch-circuit fuses do not have to be marked with their ampere rating.
False Note: NEC 240.60(C) requires fuses to be marked with their ampere rating, and 240.83(A) requires circuit breakers to be marked with their ampere rating.
When determining the overcurrent protection requirements for transformers in a circuit, other requirements from Article(s) ? may also need to be investigated.
I., II., and III.
For a transformer 1,000 volts or less, with a secondary current of five amperes, the secondary overcurrent protective device could be sized up to ? of the transformer-rated current where both primary and secondary protection is provided.
167% 450.3(B)
The minimum ampacity rating and size of the copper THW branch-circuit conductors for a 3-phase, 125-horsepower, 460-volt squirrel cage induction motor is ? and a ? conductor. The terminals are rated 75°C.
195 A / 3/0 AWG Table 430.250
The motor-compressor branch-circuit short-circuit and ground-fault protective device shall be capable of carrying the starting current of the motor. A protective device having a rating or setting not exceeding 175% of the motor-compressor rated load current or branch-circuit selection current, whichever is greater, shall be permitted, provided that where the protection specified is not sufficient for the starting current of the motor, the rating or setting shall be permitted to be increased, but shall not exceed ? of the motor rated load current or branch-circuit selection current, whichever is greater.
225% 440.22(A)
When determining the conductor ampacity and motor branch-circuit short-circuit and ground-fault protective device ampere rating, ? is the full-load current used for the calculation for a 7 1/2-horsepower, 3-phase, 208-volt induction-type squirrel cage motor.
24.2 A Table 430.250
Determine the maximum overload protection trip or rating for a 3-phase, 75-horsepower, 240-volt squirrel cage motor with a nameplate current of 188 amperes, a temperature rise of 40°C, and a marked service factor of 1.15 when starting current is not a problem.
Max. overload protection for marked service factor of 1.15 or marked temperature rise of 40°C is 125% of the nameplate rating per 430.32(A)(1). Overload protection = 188 × 1.25 = 235 A
Determine the branch-circuit conductor size (copper, THW) needed for a 3-phase, 75-horsepower, 240-volt squirrel cage motor with a nameplate current of 188 amperes, a temperature rise of 40°C, and a marked service factor of 1.15 when starting current is not a problem. The terminals are rated 75°C.
Table 430.250 shows full-load current to be 192 amperes for the 75-horsepower motor. Conductor ampacity = Table amperes × 125% = 192 × 1.25 = 240 A Table 310.16 requires 250 kcmil conductors
Determine the maximum rating of time-delay fuses needed for a 3-phase, 75-horsepower, 240-volt squirrel cage motor with a nameplate current of 188 amperes, a temperature rise of 40°C, and a marked service factor of 1.15 when starting current is not a problem. Assume the motor will start with this selection.
Table 430.250 shows full-load current to be 192 amperes for the 75-horsepower motor. Max. time-delay fuse size = Table amperes × 175% = 192 × 1.75 = 336 A 430.52(C)(1) Ex. No. 1 allows the next higher standard rating. Max. Fuse size = 350 A
Which statement about supplementary protectors is not correct?
They are suitable for branch-circuit protection
A 600-volt or less branch-circuit OCPD can be identified as being current limiting by being marked "current limiting."
True
A circuit breaker with an arc reduction maintenance switch (ARMS) provides an option where lower arc flash hazard levels can be achieved when it is necessary to do energized work.
True
A fully rated system is one in which all of the overcurrent protective devices have an individual interrupting rating at least as great as the available fault current at their point of application.
True
A motor branch-circuit disconnect listed to UL 98 or UL 489 can be used as a within sight of the motor disconnect.
True
The minimum size copper THW conductor for branch-circuit conductors supplying a 10-horsepower, 230-volt, single-phase AC motor is ? . The terminals are rated at 75°C.
6 AWG Table 310.16
A transformer supplying a fire pump is not permitted to have secondary overcurrent protection.
True
Each class of current-limiting fuse has its own unique physical dimensions so that fuses of a different class are not interchangeable. For instance, Class R fuses cannot be installed in Class J fuse equipment.
True
The transformer primary overcurrent protective device supplying a fire pump must be rated to carry the sum of the locked-rotor current of the fire and pressure pump motors plus the full-load current of the accessory equipment.
True
Motor branch-circuit short-circuit and ground-fault protection and motor overload protection shall be permitted to be combined in a single protective device where the rating or setting of the device provides the overload protection specified in 430.32.
True 430.55
Which fuse type is not a branch-circuit OCPD?
UL-recognized high-speed fuse
Size the copper THW conductors needed to feed one 25-horsepower, 480-volt, 3-phase motor-compressor with a rated load current of 42 amperes and a branch-circuit selection current (BCSC) of 45 amperes when starting current is not a problem. The terminals are rated 75°C.
Use the BCSC per 440.32 Conductor ampacity = BCSC × 125% = 45 × 1.25 = 56.25 A Table 310.16 requires 6 AWG conductors
Which of the following is a motor circuit function discussed in this lesson?
a. "At the motor" or "in sight from the motor" disconnect b. Motor branch-circuit and controller disconnect c. Motor controller
A transformer utilizing primary and secondary protection with a primary current of 100 amperes at 480 volts and a secondary current of 200 amperes at 240 volts would have the primary overcurrent protection sized at a maximum of ? and the secondary overcurrent protection sized at a maximum of ? .
250 A / 250 A Table 450.3(B)
For a wye-start, delta-run connected motor, the ampacity of the branch-circuit conductors on the line side of the controller shall not be less than 125% of the motor full-load current as determined by 430.6(A)(1). The ampacity of the conductors between the controller and the motor shall not be less than ? of the motor full-load current rating as determined by 430.6(A)(1).
72% 430.22(C)
Branch-circuit conductors supplying a single motor compressor shall have an ampacity not less than 125% of either the motor-compressor rated load current or the branch-circuit selection current, whichever is greater. For a wye-start, delta-run connected motor-compressor, the selection of branch-circuit conductors between the controller and the motor-compressor shall be permitted to be based upon ? of either the motor-compressor rated-load current or the branch-circuit selection current, whichever is greater.
72% 440.32
Because of the ? impedance path, a 3-phase bolted short-circuit condition is typically assumed to be the highest level of fault current.
low
Each motor used in a continuous-duty application and rated more than one horsepower is required to be protected against overload. Which of the following is permitted to protect such motors from overload?
a. A thermal protector integral with the motor, approved for use with the motor it protects on the basis that it will prevent dangerous overheating of the motor due to overload and failure to start b. A protective device integral with a motor that will protect the motor against damage due to failure to start if the motor is part of an approved assembly that does not normally subject the motor to overloads
