NCCER Level 3 Electrical Trainee Guide 1.2.1 Temperature Rating
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(The following text(s) was copied off of my private school's online textbook)
NEC Section 110.14(C) states that the lowest temperature rating of any component in a branch circuit must be used to determine the ampacity rating of the branch circuit conductors. The lowest temperature rating could be found on a circuit breaker, a fuse, a receptacle, conductors, or any other part of the circuit. When a component has a lower rating than the others, conductors with a higher temperature rating can be used to compensate, per NEC Section 310.16....
(NEC Section: 110.14(C): https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/1/general#110.14_(C)
NEC Section 310.16: https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/3/wiring-methods-and-materials#310.16 )
NEC Section 110.14(C) states that the lowest temperature rating of any component in a branch circuit must be used to determine the ampacity rating of the branch circuit conductors. The lowest temperature rating could be found on a circuit breaker, a fuse, a receptacle, conductors, or any other part of the circuit. When a component has a lower rating than the others, conductors with a higher temperature rating can be used to compensate, per NEC Section 310.16....
(NEC Section: 110.14(C): https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/1/general#110.14_(C)
NEC Section 310.16: https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/3/wiring-methods-and-materials#310.16 )
[NFPA 70, (NEC) complete download, sometimes up.codes doesn't have absolutely everything like a certain chart so I need to pull up the .PDF of the NFPA, I use up.codes 90% of time but there's usually that one occasion or two:
https://z-library.im/dl/dKR34kyAvw
NEC Section: 110.14(C): https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/1/general#110.14_(C)
NEC Section: 310.16: https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/3/wiring-methods-and-materials#310.16
Free account required for up.codes, use this link to search with it because their native search engine is mid: https://www.google.com/search?q=up.codes+yourSectionNumberHere
Always remember to read the first statement of a section if it's lettered like 110.14(C), read the beginning paragraph of that section which would be 110.14 in this case since it may modify its lettered parts. Source where I heard this: https://www.youtube.com/watch?v=TThuFGH5K3I ]
https://z-library.im/dl/dKR34kyAvw
NEC Section: 110.14(C): https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/1/general#110.14_(C)
NEC Section: 310.16: https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/3/wiring-methods-and-materials#310.16
Free account required for up.codes, use this link to search with it because their native search engine is mid: https://www.google.com/search?q=up.codes+yourSectionNumberHere
Always remember to read the first statement of a section if it's lettered like 110.14(C), read the beginning paragraph of that section which would be 110.14 in this case since it may modify its lettered parts. Source where I heard this: https://www.youtube.com/watch?v=TThuFGH5K3I ]
(The following text(s) was copied off of my private school's online textbook)
...For example, if the termination rating of a circuit breaker is 140°F (60°C), the ampacity rating of the conductors cannot exceed the value given in the 140°F (60°C) column of NEC Table 310.16 for overcurrent protection. However, if the branch circuit conductor has a higher temperature rating, such as THHN wire rated at 194°F (90°C), the higher ampacity rating can be used for ampacity adjustment, correction, or both...
(NEC Table 310.16 https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/3/wiring-methods-and-materials#310.16 )
...For example, if the termination rating of a circuit breaker is 140°F (60°C), the ampacity rating of the conductors cannot exceed the value given in the 140°F (60°C) column of NEC Table 310.16 for overcurrent protection. However, if the branch circuit conductor has a higher temperature rating, such as THHN wire rated at 194°F (90°C), the higher ampacity rating can be used for ampacity adjustment, correction, or both...
(NEC Table 310.16 https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/3/wiring-methods-and-materials#310.16 )
(The following text(s) was copied off of my private school's online textbook)
...Example 1:
It is determined that, by combining branch circuits on a project, two costly runs of conduit can be eliminated.
The branch circuits are to be pulled in a single conduit.
All the conductors in the conduit will be current-carrying conductors of the same size and insulation type.
What is the derated ampacity for each of eight No. 12 THHN copper conductors when pulled in a single conduit?
Solution:
Per NEC Table 310.16, the ampacity of No. 12 THHN is 30A. Per NEC Section 310.15(C)(1), the ampacity shown in NEC Table 310.16 must be derated to 70% of its value because there are eight current-carrying conductors:
30A times 0.7 = 21A
Thus, the new ampacity after derating is 21A....
(NEC Table 310.16: https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/3/wiring-methods-and-materials#310.16
NEC Section 310.15(C)(1): https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/3/wiring-methods-and-materials#310.15_(C)_(1) )
...Example 1:
It is determined that, by combining branch circuits on a project, two costly runs of conduit can be eliminated.
The branch circuits are to be pulled in a single conduit.
All the conductors in the conduit will be current-carrying conductors of the same size and insulation type.
What is the derated ampacity for each of eight No. 12 THHN copper conductors when pulled in a single conduit?
Solution:
Per NEC Table 310.16, the ampacity of No. 12 THHN is 30A. Per NEC Section 310.15(C)(1), the ampacity shown in NEC Table 310.16 must be derated to 70% of its value because there are eight current-carrying conductors:
30A times 0.7 = 21A
Thus, the new ampacity after derating is 21A....
(NEC Table 310.16: https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/3/wiring-methods-and-materials#310.16
NEC Section 310.15(C)(1): https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/3/wiring-methods-and-materials#310.15_(C)_(1) )
(The following text(s) was copied off of my private school's online textbook)
...Example 2:
What is the maximum load that may be connected on each of six No. 2 THWN copper conductors in a single conduit?
Solution:
Per NEC Table 310.16, the ampacity of No. 2 THWN is 115A. Per NEC Table 310.15(C)(1), the ampacity shown in NEC Table 310.16 must be derated to 80% of its value because there are six current-carrying conductors:
115A times 0.8 = 92A.
The maximum load after ampacity derating is 92A.
(NEC Table 310.16: https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/3/wiring-methods-and-materials#310.16
NEC Section 310.15(C)(1): https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/3/wiring-methods-and-materials#310.15_(C)_(1) )
Example 3:
A branch circuit is required to supply a noncontinuous load with a nameplate rating of 55A. The equipment is in a plant, located in a room with plastic extrusion equipment that gets very warm. The ambient temperature in the room is 92°F (33.3°C). What is the minimum size of THHN copper conductors allowed to supply the new load?
Solution:
Per NEC Table 310.16, No. 8 THHN copper conductors have an ampacity rating of 55A (coincidently, the same as the load of the new equipment).
Per NEC Table 310.15(B)(1)(1), the ampacity of the conductors must be multiplied by a correction factor of 0.96.
55 times 0.96 = 52.8A
The available ampacity is 52.8A.
Thus, the ampacity of No. 8 THHN copper conductors operating in an area that is 92°F (33.3°C) does not meet the requirements for a load of 55A.
The next size of wire, No. 6 THHN, has a rating of 75A.
But before selecting it, the 0.96 correction factor must also be applied to it:
75A times 0.96 = 72A
While the No. 8 THHN conductors may have looked just right at first, they aren’t acceptable. No. 6 THHN conductors will be required to power the new load, due to the heat in the area....
(NEC Table 310.15(B)(1)(1): https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/3/wiring-methods-and-materials#310.15_(B)_(1)
NEC Table 310.16: https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/3/wiring-methods-and-materials#310.16 )
...Example 2:
What is the maximum load that may be connected on each of six No. 2 THWN copper conductors in a single conduit?
Solution:
Per NEC Table 310.16, the ampacity of No. 2 THWN is 115A. Per NEC Table 310.15(C)(1), the ampacity shown in NEC Table 310.16 must be derated to 80% of its value because there are six current-carrying conductors:
115A times 0.8 = 92A.
The maximum load after ampacity derating is 92A.
(NEC Table 310.16: https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/3/wiring-methods-and-materials#310.16
NEC Section 310.15(C)(1): https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/3/wiring-methods-and-materials#310.15_(C)_(1) )
Example 3:
A branch circuit is required to supply a noncontinuous load with a nameplate rating of 55A. The equipment is in a plant, located in a room with plastic extrusion equipment that gets very warm. The ambient temperature in the room is 92°F (33.3°C). What is the minimum size of THHN copper conductors allowed to supply the new load?
Solution:
Per NEC Table 310.16, No. 8 THHN copper conductors have an ampacity rating of 55A (coincidently, the same as the load of the new equipment).
Per NEC Table 310.15(B)(1)(1), the ampacity of the conductors must be multiplied by a correction factor of 0.96.
55 times 0.96 = 52.8A
The available ampacity is 52.8A.
Thus, the ampacity of No. 8 THHN copper conductors operating in an area that is 92°F (33.3°C) does not meet the requirements for a load of 55A.
The next size of wire, No. 6 THHN, has a rating of 75A.
But before selecting it, the 0.96 correction factor must also be applied to it:
75A times 0.96 = 72A
While the No. 8 THHN conductors may have looked just right at first, they aren’t acceptable. No. 6 THHN conductors will be required to power the new load, due to the heat in the area....
(NEC Table 310.15(B)(1)(1): https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/3/wiring-methods-and-materials#310.15_(B)_(1)
NEC Table 310.16: https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/3/wiring-methods-and-materials#310.16 )
1 month ago#638116
(The following text(s) was copied off of my private school's online textbook)
...Example 4:
A branch circuit will power 16A of continuous loads. The conductors to be used are copper THHN. They will be installed in a raceway with a total of 12 current-carrying conductors and routed through an area with an ambient temperature of 105°F (40.5°C). What is the minimum wire size and overcurrent protective device required for this circuit?
(NEC Sections about to be referenced:
NEC Section 210.19: https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/2/wiring-and-protection#210.19_(A)
NEC Section 210.20(A): https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/2/wiring-and-protection#210.20_(A) )
Solution:
Per NEC Section 210.19(A)(1) for conductors and NEC Section 210.20(A) for overcurrent protection, the minimum current rating for the conductor and the overcurrent protective device is calculated by multiplying the load by 125%:
16A times 1.25 = 20A
The conductor and overcurrent protection rating required is 20A.
(NEC Sections about to be referenced:
NEC Table 310.16: https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/3/wiring-methods-and-materials#310.16
NEC Table 310.15(C)(1): https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/3/wiring-methods-and-materials#310.15_(C)_(1)
Per NEC Table 310.15(C)(1), the adjustment factor for 12 conductors is 50%. Essentially, this means that the value above must be doubled:
20A / 0.50 = 40A
Because the ambient temperature is 105°F (40.5°C), the conductor ampacity must be further derated per NEC Section 310.15(B)(1)(1):
40A / 0.87 = 45.98A
Thus, the conductor capacity required is 45.98A.
Refer to NEC Table 310.16 and find THHN under the 90°C (194°F) column. No. 8 THHN provides an ampacity of 55A, which is greater than the 45.98A required here. Therefore, the overcurrent protective device would be sized at 20A as noted in the first calculation, and the correct wire size would be No. 8 THHN....
...Example 4:
A branch circuit will power 16A of continuous loads. The conductors to be used are copper THHN. They will be installed in a raceway with a total of 12 current-carrying conductors and routed through an area with an ambient temperature of 105°F (40.5°C). What is the minimum wire size and overcurrent protective device required for this circuit?
(NEC Sections about to be referenced:
NEC Section 210.19: https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/2/wiring-and-protection#210.19_(A)
NEC Section 210.20(A): https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/2/wiring-and-protection#210.20_(A) )
Solution:
Per NEC Section 210.19(A)(1) for conductors and NEC Section 210.20(A) for overcurrent protection, the minimum current rating for the conductor and the overcurrent protective device is calculated by multiplying the load by 125%:
16A times 1.25 = 20A
The conductor and overcurrent protection rating required is 20A.
(NEC Sections about to be referenced:
NEC Table 310.16: https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/3/wiring-methods-and-materials#310.16
NEC Table 310.15(C)(1): https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/3/wiring-methods-and-materials#310.15_(C)_(1)
Per NEC Table 310.15(C)(1), the adjustment factor for 12 conductors is 50%. Essentially, this means that the value above must be doubled:
20A / 0.50 = 40A
Because the ambient temperature is 105°F (40.5°C), the conductor ampacity must be further derated per NEC Section 310.15(B)(1)(1):
40A / 0.87 = 45.98A
Thus, the conductor capacity required is 45.98A.
Refer to NEC Table 310.16 and find THHN under the 90°C (194°F) column. No. 8 THHN provides an ampacity of 55A, which is greater than the 45.98A required here. Therefore, the overcurrent protective device would be sized at 20A as noted in the first calculation, and the correct wire size would be No. 8 THHN....
1 month ago#638440
(The following text(s) was copied off of my private school's online textbook)
NEC Section 110.14(C) states that the lowest temperature rating of any component in a branch circuit must be used to determine the ampacity rating of the branch circuit conductors. The lowest temperature rating could be found on a circuit breaker, a fuse, a receptacle, conductors, or any other part of the circuit. When a component has a lower rating than the others, conductors with a higher temperature rating can be used to compensate, per NEC Section 310.16....
(NEC Section: 110.14(C): https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/3/wiring-methods-and-materials#310.14_(C)
NEC Section 310.16: https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/3/wiring-methods-and-materials#310.16 )
[[This is the only part I didn't really understand, the rest of the reading makes sense thus far though]](The following text(s) was copied off of my private school's online textbook)
...For example, if the termination rating of a circuit breaker is 140°F (60°C), the ampacity rating of the conductors cannot exceed the value given in the 140°F (60°C) column of NEC Table 310.16 for overcurrent protection. However, if the branch circuit conductor has a higher temperature rating, such as THHN wire rated at 194°F (90°C), the higher ampacity rating can be used for ampacity adjustment, correction, or both...
(NEC Table 310.16 https://up.codes/viewer/nfpa/nfpa-70-2023/chapter/3/wiring-methods-and-materials#310.16 )
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