20a 120v (2) networks #12 THHN derating

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After all is said and done, per nec I still don't have a clear answer if 2 full networks of thhn (8) #12s are compliant in a conditioned 75 degree room on a regular ge bolt on breaker?

If i have to debate and due to circuit breaker lug rating?
 
infinity said:
No. The terminal doesn't change the adjusted conductor ampacity. You have 6 CCCs which gives you an adjusted ampacity 24 amps.
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I've seen and read so many debates on derating and including the neutral as a ccc. Effectively reducing ampacity to 21a. But I thought the circuit rating was based on the weakest link which in this case is a ge thqb bolt on breaker rated @75c not 90 like the wire
 
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Pipeandwire said:
I've seen and read so many debates on derating and including the neutral as a ccc. Effectively reducing ampacity to 21a. But I thought the circuit rating was based on the weakest link which in this case is a ge thqb bolt on breaker rated @75c not 90 like the wire
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There isn't really anything to debate. You haven't established that these circuits are more than 50% harmonic so the neutral does not count as a CCC. That leaves you with 6 CCCs and an adjusted ampacity of 24 amps. Then you look at the terminal rating if it's 75° C then you can use the 75 degree C conductor rating which is 25 amps. However Article 240 will tell you that in this case a #12 conductor cannot exceed 20 amps. Since your adjusted conductors are 24 amps and you terminal is good for 25 amps you're good with using #12 THHN for your 20 amp circuits after they have been derated.
 
infinity said:
There isn't really anything to debate. You haven't established that these circuits are more than 50% harmonic so the neutral does not count as a CCC. That leaves you with 6 CCCs and an adjusted ampacity of 24 amps. Then you look at the terminal rating if it's 75° C then you can use the 75 degree C conductor rating which is 25 amps. However Article 240 will tell you that in this case a #12 conductor cannot exceed 20 amps. Since your adjusted conductors are 24 amps and you terminal is good for 25 amps you're good with using #12 THHN for your 20 amp circuits after they have been derated.
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Can you clarify exactly what is 50% harmonic and what devices increase that load?
 
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You can see the definition at the bottom of this explanation. More and more non-linear loads are becoming a thing if the past.
Neutral conductors:
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Here's some examples of when to count and not count the neutral as a current carrying conductor or CCC:
3Ø- 208Y/120 or 480Y/277 volt system-different circuit types:
A) 2 wire circuit w/ 1 ungrounded, 1 neutral = 2 CCC's
B) 3 wire circuit w/ 2 ungrounded, 1 neutral = 3 CCC's
C) 4 wire circuit w/ 3 ungrounded, 1 neutral = 3 CCC's*
Notes:
A) A normal 2 wire circuit has equal current flowing in each of the circuit conductors so they both count as CCC's.
B) In this circuit the neutral current will be nearly equal to the current in the ungrounded conductors so the neutral counts as a CCC
C) In this circuit the neutral will only carry the imbalance of the current between the three ungrounded conductors so it is not counted as a CCC, with an exception,
*if the current is more than 50% nonlinear (see below for NEC article 100 definition) then the neutral would count as a CCC.

1Ø- 120/240 volt system-different circuit types:
D) 2 wire circuit w/ 1 ungrounded, 1 neutral = 2 CCC's
E) 3 wire circuit w/ 2 ungrounded, 1 neutral = 2 CCC's
Notes:
D) A normal 2 wire circuit has equal current flowing in each of the circuit conductors so they both count as CCC's.
E) In this circuit the neutral will only carry the imbalance between the two ungrounded conductors so the neutral is not counted as a CCC.
Nonlinear Load. A load where the wave shape of the steady-state current does not follow the wave shape of the applied voltage.
Informational Note: Electronic equipment, electronic/electric-discharge lighting, adjustable-speed drive systems, and similar equipment may be nonlinear loads.
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infinity said:
You can see the definition at the bottom of this explanation. More and more non-linear loads are becoming a thing if the past.

Thats great information, thank you. Basically have 68 benches with computers monitors and local printers. There are feeds that have 208v devices but those I have in different runs anyway. But each network 3h 1n feeds a line of benches
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The computer and monitor power supply are a 'classic' example of nonlinear loads which introduce harmonic currents.

'Classic' in two senses of the word.

These power supplies created large harmonic currents in the past, and are commonly used as examples of non linear loads.

However new regulations require power factor correction and thus limit the actual harmonic loading in modern computer power supplies.

In the installation being discussed here, I'd probably count the neutral as a CCC, but I wouldn't stress it too much.

Jon
 
winnie said:
The computer and monitor power supply are a 'classic' example of nonlinear loads which introduce harmonic currents.



'Classic' in two senses of the word.



These power supplies created large harmonic currents in the past, and are commonly used as examples of non linear loads.



However new regulations require power factor correction and thus limit the actual harmonic loading in modern computer power supplies.



In the installation being discussed here, I'd probably count the neutral as a CCC, but I wouldn't stress it too much.
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Thank you. It's always just been easier to assume it as such. And throughout my career we've typically always pulled 10's for a network at or above 100'
winnie said:
Jon
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@Pipeandwire
When you quote someone using the "reply" icon under the post, start your text below the quoted post. It will be below the vertical orange line on the left. It's hard to distinguish between the post you're quoting and the new text you're adding.
 
Pipeandwire said:
I've seen and read so many debates on derating and including the neutral as a ccc. Effectively reducing ampacity to 21a. But I thought the circuit rating was based on the weakest link which in this case is a ge thqb bolt on breaker rated @75c not 90 like the wire
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There is two separate ampacities that need to be calculated. First one is based on termination temperature. You must always have a conductor with at least the termination temp ampacity - so 12 AWG is fine here with a 20 amp breaker, even if it would been a breaker with 60C terminals.

Next is ampacity for insulation - that is where ambient temp and number of conductors in raceway might force you to increase the conductor size. You might have temperature conditions somewhere in the raceway that do not exist at the breaker or at the load end of said conductors and therefore need to "adjust" ampacity of the conductor to account for it. Adjustments will lessen the conductor ampacity nearly all the time, though it is possible to increase it in low ambient temperature conditions, but you still can not use lesser conductor size than the termination temp ampacity allows.
 
Even if you would like to treat the neutral as a CCC, which effectively means (8) CCC for a 70% derating, you would still be able to put (2) MWBCs using THHN #12s in a single conduit. Refer to 310.15(A), which states the following:

310.15 Ampacity Tables.
(A) General. Ampacities for conductors rated 0 volts to 2000 volts shall be as specified in the Ampacity Table 310.16 through Table 310.21, as modified by 310.15(A) through (F) and 310.12. Under engineering supervision, ampacities of sizes not shown in ampacity tables for conductors meeting the general wiring requirements shall be permitted to be deter-mined by interpolation of the adjacent conductors based on the conductor’s area. The temperature correction and adjustment factors shall be permitted to be applied to the ampacity for the temperature rating of the conductor, if the corrected and adjusted ampacity does not exceed the ampacity for the temperature rating of the termination in accordance with the provisions of 110.14(G).

You may derate based on the temperature rating of the conductor as long as the corrected and adjusted ampacity does not exceed the ampacity for the temperature rating at the termination

#12 THHN is rated for 30A at 90 degrees C, which is then adjusted at 70% to 21A at 90 degrees C. This is less than the 75 degree ampacity of #12s which is 25A so this adjusted ampacity of 21A is used. However, the small conductor rule of 240(D)(5) is then applied to limit the ampacity of #12 CU further to 20A. Note that I am assuming that you are using the THHN rating of the conductor. If this is a wet location where THWN insulation is required, you would not be able to use the 90 degree column as small conductors <#8s are typically not rated for THWN-2.
 
PD1972 said:
#12 THHN is rated for 30A at 90 degrees C, which is then adjusted at 70% to 21A at 90 degrees C. This is less than the 75 degree ampacity of #12s which is 25A so this adjusted ampacity of 21A is used. However, the small conductor rule of 240(D)(5) is then applied to limit the ampacity of #12 CU further to 20A. Note that I am assuming that you are using the THHN rating of the conductor. If this is a wet location where THWN insulation is required, you would not be able to use the 90 degree column as small conductors <#8s are typically not rated for THWN-2.
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I see that Southwire listes their Simpull as THHN/THWN up to #10 AWG. Other companies like Encore have THHN/THWN-2 in sizes smaller than #8.
 
infinity said:
I see that Southwire listes their Simpull as THHN/THWN up to #10 AWG. Other companies like Encore have THHN/THWN-2 in sizes smaller than #8.
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TIL. I never noticed that; I am just so used to looking at the Southwire data sheet that I assumed their listing standards were indicative of what the rest of the wire manufacturers followed.
 
PD1972 said:
TIL. I never noticed that; I am just so used to looking at the Southwire data sheet that I assumed their listing standards were indicative of what the rest of the wire manufacturers followed.
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That would be nice if they were all the same. Certainly make it easier on engineers, installers, and inspectors.
 
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