Lesson 3 Codes and Standards
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. Select one: a.50% b.72% c.115% d.125%
125% 430.32 (a)(1)
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). a. 50% b. 62.5% c. 72% d. 125%
125% 430.22
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. a. 125 A / 1/0 AWG b. 156 A / 2/0 AWG c. 195 A / 3/0 AWG d. 210 A / 4/0 AWG
195 A / 3/0 AWG 430.22 Note: Table 430.250 = 156 amperes 430.22 = 156 × 1.25 = 195 A Table 310.16 75°C column = 3/0 AWG THW conductor
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. a. 72% b. 115% c. 125% d. 225%
225% 440.22 (A) Note: Review the Exception to 440.22(A) indicating that the rating of the branch circuit short-circuit and ground-fault protective device shall not be required to be less than 15 amperes.
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. a. 22.0 A b. 24.2 A c. 25.3 A d. 30.2 A
24.2A TABLE 230.25
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. a. 30 A b. 45 A c. 50 A d. 60 A
30 A 240.6(A) Note: Table 430.250 = 16.7 amperes Table 430.52 = 16.7 × 1.75 = 29.23 A 430.52(C)(1) Exception 1 (round up to next standard size OCPD) 240.6(A) = 30 amperes
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. a. 30 A b. 35 A c. 40 A d. 50 A
35 A 240.6(A) Note: Table 430.248 = 17 amperes 430.52 (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. It must be the next lower size because we cannot exceed 225% of the full load current when starting is an issue.
NEC ? covers the requirements for the motor controller disconnecting means. Select one: a.430.102(A) b.430.109 c.430.111 d.430.225
430.102 (A) Go to section IX
The type of motor disconnecting means is covered by NEC ? . Select one: a.430.102(A) b.430.109 c.430.111 d.430.225
430.109
A horsepower-rated switch or circuit breaker is permitted as both the motor controller and disconnecting means in accordance with NEC ? . Select one: a.430.102(A) b.430.109 c.430.111 d.430.225
430.111
The requirements for motor-circuit overcurrent protection for motors over 1,000 volts are covered in what section of Article 430? Select one: a.430.102(A) b.430.109 c.430.111 d.430.225
430.225
Which NEC article applies to electric motor-driven air-conditioning and refrigerating equipment and to the branch circuits and controllers for such equipment? a.430 b.440 c.445 d.450
440
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). a. 50% b. 62.5% c. 72% d. 125%
62.5% 430.22(D) Note: The multiplier of 62.5% is obtained by multiplying 50% by 1.25.
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. a. 1/0 AWG b. 2 AWG c. 4 AWG d. 6 AWG
6AWG 430.22 Note: Table 430.248 = 50 amperes 430.22 = 50 × 1.25 = 62.5 A Table 310.16 75°C column = 6 AWG THW conductor 110.14(C)(1) permits the use of the 75°C ampacity for this application.
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. a. 72% b. 115% c. 125% d. 225%
72% 440.32
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). a. 50% b. 62.5% c. 72% d. 125%
72% 430.22 (C) Note: The individual motor circuit conductors of a wye-start, delta-run connected motor carry 58% of the rated load current. The multiplier of 72% is obtained by multiplying 58% by 1.25.
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 c. Motor overload protection d. Both a. and b. e. Both a. and c.
Ampacity of Conductors and Branch Circuit short circuit and ground fault protection. 430.6 (a)(1) Motor overload is identified in 430.6 (a)(2) protection calculations are found in 430.32 and go of of the plate rating.
Separate motor overload protection shall be based upon the motor nameplate ? rating. a. current b. efficiency c. power d. voltage
Current 430.6(A)(2)
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? Select one: 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 c.Either a. or b. d.Neither a. nor b.
Either a. or b. 430.32(A)(2) and 430.32(A)(3). Either a. or b.
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. a. higher b. lower
Higher 430.52 (c)(1) Exception No. 1
Part ? of Article 430 covers the requirements for the motor disconnecting means. Select one: a.IV b.VII c.IX d.XI
IX Also found in the index
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 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.
Note: 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 350
The minimum ampacity for branch-circuit conductors supplying a 75-horsepower, 3-phase, induction-type squirrel cage motor that operates at 460 volts is ? . a.77 A b.96 A c.120 A d.192 A
Note: The ampacity of 96 amperes (per Table 430.250) is multiplied by 125% (per 430.22). The correct answer is: 120 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 The correct answer is: 250
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.
The correct answer is: 70 Note: 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). However, if this ampere rating is not sufficient for compressor starting current, the ampere rating can be increased but shall not exceed 225% of the motor rated load current.
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. Select one: True False
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. a. True b. False
True 430.55
The motor branch-circuit short-circuit and ground-fault protective device shall be capable of carrying the starting current of the motor. a. True b. False
True 430.52 (B)
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
Part ? of Article 430 covers the requirements for motor controllers. a.IV b.VII c.IX d.XI
VII It says so in the index
Overload protection for continuous-duty motors one horsepower or less, automatically started, is covered by NEC ? . Select one: a.430.6(A)(1) b.430.22(C) c.430.32(B) d.430.52(C)(1)
c.430.32(B)
