110.14(C)(1)

[Brigman]

Referring to 110.14(C)(1) that references Table 310.15(B)(16) for determining the allowable ampacities for terminations. If I understand correctly please confirm or clarify the following presumption:

If 500 kcmil is rated the maximum termination of 380 amp @ 75 deg C. If I install cable tray that allows me to rate the same cable at 620 amps 310.15(B)(17).

Q. Because of the cable tray and higher amperage ratting is it permissible to splice (2) 350 kcmil's and terminate to the 75 deg C connection?

 

[charlie b]

Your question has me confused. The temperature rating at the top of each of the three columns in table 310.15(B)(16) is not about terminations. It is about the ability of the conductor's insulation system to withstand higher temperatures. The conductor types that are listed in the 60C column can withstand a temperature increase of 60 degrees C over an ambient temperature of 30C. A conductor that has THHN insulation (being listed under the 90C column) can withstand a temperature increase of 90 degrees C over an ambient temperature of 30C. Where terminations come into play is that you cannot use the ampacity ratings in the 90C column, if the terminations to which you will attach the conductors are only listed for 75C. That is stated in 110.14(C).

With this in mind, would you please state your question in some other way, so that I can understand what you are trying to ask?

Welcome to the forum.

 

[jim dungar]

Q. Because of the cable tray and higher amperage ratting is it permissible to splice (2) 350 kcmil's and terminate to the 75 deg C connection?

Yes, it is permissible to splice conductors together so that the terminated end is applied correctly to the terminal. The length of the 'added' conductor is never mentioned, however most people accept 4' as that is what is used in UL testing for terminations.

 

[Brigman]

Clarification

Clarification

To help clarify; After reading 110.14 (C) it appears to limit allowable ampacities to table 310.15(B)(16) for any termination. That said, when using cable tray (free air ratings) 310.15(B)(17) you are allowed to rate at 610 amps but are limited at the termination to 310.15(B)(16) of 380 amps. At this point leaving the solution of increasing the amount of conductors in this installation or splicing (2) 350 kcmill's at the closest point and terminating.

For the sake of installation cost, we can reduce the overall project cost by installing cable tray but the termination now requires a modification to allow for 310.15(B)(16). Do I understand correctly? If not, what am I missing?

 

[Smart $]

To help clarify; After reading 110.14 (C) it appears to limit allowable ampacities to table 310.15(B)(16) for any termination. That said, when using cable tray (free air ratings) 310.15(B)(17) you are allowed to rate at 610 amps but are limited at the termination to 310.15(B)(16) of 380 amps. At this point leaving the solution of increasing the amount of conductors in this installation or splicing (2) 350 kcmill's at the closest point and terminating.

For the sake of installation cost, we can reduce the overall project cost by installing cable tray but the termination now requires a modification to allow for 310.15(B)(16). Do I understand correctly? If not, what am I missing?

If I understand you correctly, you want to convert a run of single conductor (500kcmil) to parallel (two 350kcmil) just prior to its termination to make the entire run rating 620A before applying any adjustment and correction factors. That will work! ...but you will likely have to do it at both ends of the run and the length of the 350's will have to be 4' or greater (according to popular belief).

 

[Smart $]

Your question has me confused. The temperature rating at the top of each of the three columns in table 310.15(B)(16) is not about terminations. It is about the ability of the conductor's insulation system to withstand higher temperatures. The conductor types that are listed in the 60C column can withstand a temperature increase of 60 degrees C over an ambient temperature of 30C. A conductor that has THHN insulation (being listed under the 90C column) can withstand a temperature increase of 90 degrees C over an ambient temperature of 30C. Where terminations come into play is that you cannot use the ampacity ratings in the 90C column, if the terminations to which you will attach the conductors are only listed for 75C. That is stated in 110.14(C).

With this in mind, would you please state your question in some other way, so that I can understand what you are trying to ask?

Welcome to the forum.

Can you cite an authoritative reference which states the conductor insulation temperature rating is based on temperature rise above a 30?C ambient?

To the best of my knowledge, the 60?C, 75?C, and 90?C ratings are absolute temperatures... not temperature rise above ambient.

 

[texie]

Your question has me confused. The temperature rating at the top of each of the three columns in table 310.15(B)(16) is not about terminations. It is about the ability of the conductor's insulation system to withstand higher temperatures. The conductor types that are listed in the 60C column can withstand a temperature increase of 60 degrees C over an ambient temperature of 30C. A conductor that has THHN insulation (being listed under the 90C column) can withstand a temperature increase of 90 degrees C over an ambient temperature of 30C. Where terminations come into play is that you cannot use the ampacity ratings in the 90C column, if the terminations to which you will attach the conductors are only listed for 75C. That is stated in 110.14(C).

With this in mind, would you please state your question in some other way, so that I can understand what you are trying to ask?

Welcome to the forum.

Charlie, would it not be more correct to say that, for example, based on Table 310.15(B)(16) a 1/0 CU conductor with a load of 150 amps would not exceed 75 degree C in temperature at an ambient of 30 degree C? And the same conductor would be operating at 85 degree C if the ambient was 40 degree C?

 

[texie]

Referring to 110.14(C)(1) that references Table 310.15(B)(16) for determining the allowable ampacities for terminations. If I understand correctly please confirm or clarify the following presumption:

If 500 kcmil is rated the maximum termination of 380 amp @ 75 deg C. If I install cable tray that allows me to rate the same cable at 620 amps 310.15(B)(17).

Q. Because of the cable tray and higher amperage ratting is it permissible to splice (2) 350 kcmil's and terminate to the 75 deg C connection?

As others have indicated, this would be allowable assuming you have 4 or more feet from the splice point to the 75 degree termination. I might add that you also have to be sure the splice device is rated for 90 degree C.

It would seem to me that you could have even a more extreme case of this. For example, if you met the requirements of 392.80(A)(2)(c) and used 500 CU THHN the ampacity could be as high as 700 amp and splice to 2, 500 CU THHN to attach the the 75 degree C termination.

 

[Smart $]

... I might add that you also have to be sure the splice device is rated for 90 degree C.

Good point. If he used a 75?C splice device he would just be re-creating the same situation at the splice.

It would seem to me that you could have even a more extreme case of this. For example, if you met the requirements of 392.80(A)(2)(c) and used 500 CU THHN the ampacity could be as high as 700 amp and splice to 2, 500 CU THHN to attach the the 75 degree C termination.

He didn't provide all the necessary details to determine final ampacity, but it seems to me he will have to do this if he needs to keep the final ampacity close to the conductor rating at the 75?C value (620A). If he doesn't space the 500's one cable diameter, he would have to derate to 65% (455A). If some of the 350's and the splices end up in the tray, the same spacing would apply to the 350's, unless permitted to be ignored under 310.15(A)(2) Exception... so parallel 500's may not be necessary for the terminations

 

[charlie b]

Can you cite an authoritative reference which states the conductor insulation temperature rating is based on temperature rise above a 30?C ambient?

Sure! Just give me 10 minutes, and then check Wikipedia. :happyyes: :lol:


OK, OK. I took another look at table 310.13(A). Now I won't say that I have been interpreting the whole temperature rise thing wrong. :happysad: But I might have been a bit short on having it right. :ashamed1:

 

[Brigman]

More details

More details

Great information. So now let me give you the real life application details and see if I can tie this together. In the original design the following are the details:
Total Load = 3274 amps
Using the 620 amp rating we can install 6 X 500 kcmil's in a cable tray.
If we have to use the lower rating because of the termination factor we will have to install 9 x 500 kcmill's.

With the following assumptions;

1. Utilizing the 620 amp rating installed in cable tray.
2. Splice 2 X 350 kcmill's on each conductor and the breaker termination (note, the line side is derived from the transformer buss)
3. The splice is rated at the higher calculation.

Is this application permissible? If not do you have any suggestions?

 

[Smart $]

Great information. So now let me give you the real life application details and see if I can tie this together. In the original design the following are the details:
Total Load = 3274 amps
Using the 620 amp rating we can install 6 X 500 kcmil's in a cable tray.
If we have to use the lower rating because of the termination factor we will have to install 9 x 500 kcmill's.

With the following assumptions;

1. Utilizing the 620 amp rating installed in cable tray.
2. Splice 2 X 350 kcmill's on each conductor and the breaker termination (note, the line side is derived from the transformer buss)
3. The splice is rated at the higher calculation.

Is this application permissible? If not do you have any suggestions?

What is the rating of the breaker? Your transformer secondary conductors' ampacity cannot be less than the breaker rating [240.21(C) general statement, last sentence {doesn't really matter over 800A}].

Unless the transformer is listed and identified for using 90?C-rated conductors, you will have to use the termination temperature transition at the transformer end, too [110.14(C)(1)(b)(2)].