Derating # of CCC

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SiddMartin

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I need to better understand derating of CCC in a conduit.
I am using #12 THHN cu, and in a conduit longer then 24", to derate, can I use the 90 deg. column? I believe I can and thus I figure this:

#12 is rated at 30Amps. (310.16)
If I have (7-9) #12 CCC's then 30 * 70% = 21 Amps . Am I okay to still protect the #12's w/ a 20A breaker? I think I am.

now if I have (10) #12 CCC then 30 * 50% = 15A, I would have to either protect the #12's w/ 15A breaker or upsize to #10 THHN. Am I correct in thinking this>? I believe so b/c (10) #10 CCC is 40A * 50 = 20A,

am I missing something to the equation or am I correct?
I am only questioning solution to derating the # of CCC, not anything else

Thank you in advance
 
SiddMartin said:
I need to better understand derating of CCC in a conduit.
I am using #12 THHN cu, and in a conduit longer then 24", to derate, can I use the 90 deg. column? I believe I can and thus I figure this:

#12 is rated at 30Amps. (310.16)
If I have (7-9) #12 CCC's then 30 * 70% = 21 Amps . Am I okay to still protect the #12's w/ a 20A breaker? I think I am.

now if I have (10) #12 CCC then 30 * 50% = 15A, I would have to either protect the #12's w/ 15A breaker or upsize to #10 THHN. Am I correct in thinking this>? I believe so b/c (10) #10 CCC is 40A * 50 = 20A,

am I missing something to the equation or am I correct?
I am only questioning solution to derating the # of CCC, not anything else

Thank you in advance
Click to expand...
You are 100% correct!
 
SiddMartin said:
can I use the 90 deg. column? I believe I can and thus I figure this:
Click to expand...
110.14 (c) allows it
110.14
(C) Temperature Limitations. The temperature rating associated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected termination, conductor, or device. Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both.
 
SiddMartin said:
...can I use the 90 deg. column? ....
Click to expand...


Derating for more than 3 CCCs starts at 310.15(B)(2)(a), and does not reference 110.14 at all. You use whatever column of T310.16-19 based on the insulation of the conductor you are calculating. And you use the values given in Tables 310.16 through -19 (as per column 2 or T310.15(B)(2)(a)).
 
480sparky said:
Derating for more than 3 CCCs starts at 310.15(B)(2)(a), and does not reference 110.14 at all. You use whatever column of T310.16-19 based on the insulation of the conductor you are calculating. And you use the values given in Tables 310.16 through -19 (as per column 2 or T310.15(B)(2)(a)).
Click to expand...

What allows you to use 90 degree column for derating?
 
480sparky said:
Derating for more than 3 CCCs starts at 310.15(B)(2)(a), and does not reference 110.14 at all.
Click to expand...

In a corrections factor example the NECH had this to say
"STEP 2.
Select cable. From Table 400.5(B), a 3/0 AWG copper Type W portable power cable has an ampacity of 274 amperes from the 90?C, F column. In accordance with 110.14, the 90?C cable ampacity can be used where it is required to ?derate? the cable ampacity. For this particular installation, both an ambient temperature correction factor and an ampacity adjustment factor for more than 3 current-carrying conductors in the cable have to be applied."
 
Twoskinsoneman said:
What allows you to use 90 degree column for derating?
Click to expand...

The words in the heading of the second column of T310.15(B)(2)(a): "... Values in Table 310.16 through 310.19...."

Go to T310.16. What are the numbers there? That's what you start with.

310.15(B)(2)(a) says nothing about the temperature limitations of the terminals. You are designing one component of a circuit here. When you are done, you can go to 110.14(C)(1)(a) and/or 240.4(D) and continue.
 
480sparky said:
That's what you start with.
Click to expand...

I disagree, IMO we have to start with the last sentence of 110.14(C).


"Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both."
 
480sparky said:
The words in the heading of the second column of T310.15(B)(2)(a): "... Values in Table 310.16 through 310.19...."

Go to T310.16. What are the numbers there? That's what you start with.

310.15(B)(2)(a) says nothing about the temperature limitations of the terminals. You are designing one component of a circuit here. When you are done, you can go to 110.14(C)(1)(a) and/or 240.4(D) and continue.
Click to expand...


Without 110.14(C) how would you know what column to use in the first place?
 
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