Smitty’s Two Minute Drill Overcurrent Protection

Smitty’s Two Minute Drill 2017-8 Overcurrent Protection
A drill to help you improve your code skills and your ability to find answers in the code book. © Ted “Smitty” Smith 2016, 2017

Directions Left click on the presentation ICON located at the bottom of the slide directory to the left of the this slide. Each slide will transition to the correct answer automatically in 2:00 minutes. The correct answer will transition in 5 seconds. Do not worry about writing down the correct answer for now. You will have the opportunity to do that at the end of the two minute drill Good luck

Question 1 An electric arc welder is fed with a THHN 1/0 aluminum conductor. What is the maximum sized over current protective device that can be used to protect these conductors? A. 135 B. 150 C. 270 D. 300 Copyright 2017 Ted "Smitty" Smith

Question 1 Answer D. 300 T301.15(B16) determines the ampacity of a THHN 1/0 Aluminum to be 135A . 630.12(B) states that the OCPD can be no larger than 200% of the conductor ampacity. 2 x 135= 270 states that if the calculation results in a size that is not listed as a standard size in we can go up to the next standard size. 270 is not listed in 240.6, the next highest up from there is 300A. Copyright 2005 Ted "Smitty" Smith

Question 2 An overcurrent device shall be provided in each ungrounded conductor for each capacitor bank. The rating or setting of the overcurrent device shall be: A. 100% of the rated current of the capacitor bank B. 125% of the rated current of the capacitor bank C. 135% if the rated current of the capacitor bank D. As low as practicable Copyright 2016 Ted "Smitty" Smith

Question 2 Answer 460.8(B) D. as low as practicable
Copyright 2005 Ted "Smitty" Smith

Question 4 What is the maximum sized overcurrent protective device that can be used to protect non-power limited fire alarm circuit conductors which are size 16 AWG. A. 10 B. 8 C. 6 D. 4 Copyright 2017 Ted "Smitty" Smith

Question 4 Answer 760.43 A. 10 amperes

Question 5 Household type appliances with surface heating elements having a maximum demand of more than 60 amperes, calculated in accordance with T shall have their power supply subdivided into a minimum of ________ circuits, each of which shall be provided with overcurrent protection rated at not over ________ amperes. 3/30 2/50 3/40 2/40 Copyright 2005 Ted "Smitty" Smith

Question 6 What is maximum sized overcurrent protective device which can be used for a single load of 28 amperes which is fed with a 10 AWG copper conductor? A. 20A B. 25A C. 30A D. 40A Copyright 2005 Ted "Smitty" Smith

Question 6 answer 240.4(D)(7) C. 30 A

Question 7 The 1/0 THWN copper secondary conductors of a Delta/Wye three phase 480V/208V transformer may be protected with the overcurrent protection of the primary of the transformer even though the secondary conductors leave the enclosure of the transformer, as long as the primary overcurrent protection is not larger than __________________ amperes. A. 150 A B A C. 650 A D. 350 A Copyright 2005 Ted "Smitty" Smith

Question 7 answer C. 650A 240.21(C)(2)
The primary must not be larger than 10 times the ampacity of the secondary conductor if you multiply the OCPD rating times the primary to secondary voltage ratio. In this case the voltage ratio is: 480/208= 2.3 The ampacity of the secondary conductor is 150 amperes. 10 times the ampacity of the secondary is 1500 amperes. 1500/2.3 is 650A approx. Copyright 2005 Ted "Smitty" Smith

Question 9 The ampere rating of an overcurrent protective device located ahead of a motor control center that has a rating of 300 Amperes for the common power bus and is fed with 250 KCML THWN copper conductors shall not exceed _________________ amperes. A. 255 A B. 250 A C. 300 A D. 200 A Copyright 2005 Ted "Smitty" Smith

Question 9 answer C. 300 A requires the OCPD to be rated no higher than the common power bus which is 300 A (B) requires the OCPD to be rated no higher than the conductors ampacity which is 255A, however, if the conductors ampacity is not a standard size and it does not feed multiple receptacle loads and it is rated less than 800 A we can go up to the next standard size, which is 300 A according to Copyright 2005 Ted "Smitty" Smith

Question 10 A phase convertor has a single phase input full load ampere rating of 100A. The loads supplied by the phase convertor will be varied. What is the maximum rating of an inverse time circuit breaker that is will be used for overcurrent protection of the phase convertor. A. 100A B. 115A C. 110A D. 125A Copyright 2005 Ted "Smitty" Smith

Question 11 What is the maximum sized overcurrent protection that can be used for a Class 1, power limited circuit that is fed with 18 AWG copper conductors? A. 5A B. 7A C. 10A D. 15A Copyright 2017 Ted "Smitty" Smith

Question 13 answer A. True 668.3(C)(2)

Question 14 What is the minimum rating of the overcurrent protection device for an industrial, non-medical use X-ray machine that has a momentary rating of 80A and a long time rating of 50A? A. 80 A B. 50 A C. 40 A D. 25 A Copyright 2017 Ted "Smitty" Smith

Question 15 Which of the following is allowed for use as overcurrent protection for sensitive electronic equipment? A. Inverse time, single pole , 120V circuit breaker B. Inverse time, two pole, 208V circuit breaker C. Common trip, two pole, 60V/120V circuit breaker D. Instantaneous Trip, single pole, 120V circuit breaker Copyright 2005 Ted "Smitty" Smith

Question 15 C. Common trip, 2 pole, 60V/120V circuit breaker 647.4(A)

Question 16 A resistance welder is fed with a 8 AWG copper feeder conductor, THHN. What is the maximum sized inverse time circuit breaker that can be used for overcurrent protection of the feeder conductors? A. 60 A B. 165 A C. 175 A D. 300 A Copyright 2005 Ted "Smitty" Smith

Question 16 answer C 175 A 630.32(B) allows for a maximum of 300% of the conductors ampacity T310.15(B16) lists the conductors ampacity as 55A. 3 x 55= 165 A states that if the values does not match a standard size listed in 240.6, then we go up to the next higher value listed which is 175A Copyright 2005 Ted "Smitty" Smith

Question 17 Which of the following is NOT one of the approved methods to reduce clearing time for Arc Energy Reduction for a circuit breaker with the highest continuous current trip rating setting is 1200 Amperes. A. An instantaneous trip setting that is less than the available arcing current B. Zone-selective interlocking C. Universal metering adjustment D. Energy-reducing active arc flash mitigation system Copyright 2005 Ted "Smitty" Smith

Question 17 answer C. Universal Metering System
This is made up. There is no system with that name in the electrical industry. 240.87(B) Copyright 2005 Ted "Smitty" Smith

Question 18 answer C. 5000 Amperes 240.83(C)

Question 19 Fuse holders for current-limiting fuses shall permit insertion of fuses that are not current-limiting if the manufacturer instructions do not prohibit this practice. A. True B. False Copyright 2005 Ted "Smitty" Smith

Question 19 answer B. False 240.60(B)

Question 20 A three phase, 480V to 208V transformer will have secondary conductors which will be protected from overcurrent by the primary conductor’s overcurrent device. The secondary conductors will be 13 feet in length. The primary conductors are protected by a 50 Ampere inverse time circuit breaker. If nothing else is know, what is the minimum ampacity required for the secondary conductors? A. 50 A B A C A D A Copyright 2005 Ted "Smitty" Smith

Question 10 Answer D A 25’ Foot Tap rule for other than industrial locations 240.21(C)(6) The minimum ampacity of the secondary conductos must be the transformer voltage ratio ( 480/208=2.3) multiplied by 1/3 of the primary OCPD rating. (50/3=16.6) 16.6x2.3= A Copyright 2005 Ted "Smitty" Smith

End of Drill Click on this slide to continue to the repeat of the questions. The timer will not operate in this section. Click on each slide to advance. Review the questions and look up the answers. Copyright 2005 Ted "Smitty" Smith

Question 1 An electric arc welder is fed with a THHN 1/0 aluminum conductor. What is the maximum sized over current protective device that can be used to protect these conductors? A. 135 B. 150 C. 270 D. 300 Copyright 2017 Ted "Smitty" Smith

Question 1 Answer D. 300 T301.15(B16) determines the ampacity of a THHN 1/0 Aluminum to be 135A . 630.12(B) states that the OCPD can be no larger than 200% of the conductor ampacity. 2 x 135= 270 states that if the calculation results in a size that is not listed as a standard size in we can go up to the next standard size. 270 is not listed in 240.6, the next highest up from there is 300A. Copyright 2005 Ted "Smitty" Smith

Question 2 An overcurrent device shall be provided in each ungrounded conductor for each capacitor bank. The rating or setting of the overcurrent device shall be: A. 100% of the rated current of the capacitor bank B. 125% of the rated current of the capacitor bank C. 135% if the rated current of the capacitor bank D. As low as practicable Copyright 2016 Ted "Smitty" Smith

Question 2 Answer 460.8(B) D. as low as practicable

Question 4 What is the maximum sized overcurrent protective device that can be used to protect non-power limited fire alarm circuit conductors which are size 16 AWG. A. 10 B. 8 C. 6 D. 4 Copyright 2017 Ted "Smitty" Smith

Question 4 Answer 760.43 A. 10 amperes

Question 5 Household type appliances with surface heating elements having a maximum demand of more than 60 amperes, calculated in accordance with T shall have their power supply subdivided into a minimum of ________ circuits, each of which shall be provided with overcurrent protection rated at not over ________ amperes. 3/30 2/50 3/40 2/40 Copyright 2005 Ted "Smitty" Smith

Question 6 What is maximum sized overcurrent protective device which can be used for a single load of 28 amperes which is fed with a 10 AWG copper conductor? A. 20A B. 25A C. 30A D. 40A Copyright 2005 Ted "Smitty" Smith

Question 6 answer 240.4(D)(7) C. 30 A

Question 7 The 1/0 THWN copper secondary conductors of a Delta/Wye three phase 480V/208V transformer may be protected with the overcurrent protection of the primary of the transformer even though the secondary conductors leave the enclosure of the transformer, as long as the primary overcurrent protection is not larger than __________________ amperes. A. 150 A B A C. 650 A D. 350 A Copyright 2005 Ted "Smitty" Smith

Question 7 answer C. 650A 240.21(C)(2)
The primary must not be larger than 10 times the ampacity of the secondary conductor if you multiply the OCPD rating times the primary to secondary voltage ratio. In this case the voltage ratio is: 480/208= 2.3 The ampacity of the secondary conductor is 150 amperes. 10 times the ampacity of the secondary is 1500 amperes. 1500/2.3 is 650A approx. Copyright 2005 Ted "Smitty" Smith

Question 9 The ampere rating of an overcurrent protective device located ahead of a motor control center that has a rating of 300 Amperes for the common power bus and is fed with 250 KCML THWN copper conductors shall not exceed _________________ amperes. A. 255 A B. 250 A C. 300 A D. 200 A Copyright 2005 Ted "Smitty" Smith

Question 9 answer C. 300 A requires the OCPD to be rated no higher than the common power bus which is 300 A (B) requires the OCPD to be rated no higher than the conductors ampacity which is 255A, however, if the conductors ampacity is not a standard size and it does not feed multiple receptacle loads and it is rated less than 800 A we can go up to the next standard size, which is 300 A according to Copyright 2005 Ted "Smitty" Smith

Question 10 A phase convertor has a single phase input full load ampere rating of 100A. The loads supplied by the phase convertor will be varied. What is the maximum rating of an inverse time circuit breaker that is will be used for overcurrent protection of the phase convertor. A. 100A B. 115A C. 110A D. 125A Copyright 2005 Ted "Smitty" Smith

Question 11 What is the maximum sized overcurrent protection that can be used for a Class 1, power limited circuit that is fed with 18 AWG copper conductors? A. 5A B. 7A C. 10A D. 15A Copyright 2017 Ted "Smitty" Smith

Question 13 answer A. True 668.3(C)(2)

Question 14 What is the minimum rating of the overcurrent protection device for an industrial, non-medical use X-ray machine that has a momentary rating of 80A and a long time rating of 50A? A. 80 A B. 50 A C. 40 A D. 25 A Copyright 2017 Ted "Smitty" Smith

Question 15 Which of the following is allowed for use as overcurrent protection for sensitive electronic equipment? A. Inverse time, single pole , 120V circuit breaker B. Inverse time, two pole, 208V circuit breaker C. Common trip, two pole, 60V/120V circuit breaker D. Instantaneous Trip, single pole, 120V circuit breaker Copyright 2005 Ted "Smitty" Smith

Question 15 C. Common trip, 2 pole, 60V/120V circuit breaker 647.4(A)

Question 16 A resistance welder is fed with a 8 AWG copper feeder conductor, THHN. What is the maximum sized inverse time circuit breaker that can be used for overcurrent protection of the feeder conductors? A. 60 A B. 165 A C. 175 A D. 300 A Copyright 2005 Ted "Smitty" Smith

Question 16 answer C 175 A 630.32(B) allows for a maximum of 300% of the conductors ampacity T310.15(B16) lists the conductors ampacity as 55A. 3 x 55= 165 A states that if the values does not match a standard size listed in 240.6, then we go up to the next higher value listed which is 175A Copyright 2005 Ted "Smitty" Smith

Question 17 Which of the following is NOT one of the approved methods to reduce clearing time for Arc Energy Reduction for a circuit breaker with the highest continuous current trip rating setting is 1200 Amperes. A. An instantaneous trip setting that is less than the available arcing current B. Zone-selective interlocking C. Universal metering adjustment D. Energy-reducing active arc flash mitigation system Copyright 2005 Ted "Smitty" Smith

Question 17 answer C. Universal Metering System
This is made up. There is no system with that name in the electrical industry. 240.87(B) Copyright 2005 Ted "Smitty" Smith

Question 18 answer C. 5000 Amperes 240.83(C)

Question 19 Fuse holders for current-limiting fuses shall permit insertion of fuses that are not current-limiting if the manufacturer instructions do not prohibit this practice. A. True B. False Copyright 2005 Ted "Smitty" Smith

Question 19 answer B. False 240.60(B)

Question 20 A three phase, 480V to 208V transformer will have secondary conductors which will be protected from overcurrent by the primary conductor’s overcurrent device. The secondary conductors will be 13 feet in length. The primary conductors are protected by a 50 Ampere inverse time circuit breaker. If nothing else is know, what is the minimum ampacity required for the secondary conductors? A. 50 A B A C A D A Copyright 2005 Ted "Smitty" Smith

Question 10 Answer D A 25’ Foot Tap rule for other than industrial locations 240.21(C)(6) The minimum ampacity of the secondary conductos must be the transformer voltage ratio ( 480/208=2.3) multiplied by 1/3 of the primary OCPD rating. (50/3=16.6) 16.6x2.3= A Copyright 2005 Ted "Smitty" Smith

Smitty’s Two Minute Drill Overcurrent Protection

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