number of CCC in conduit

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jamesboy123

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one of the guys on the job are installing 42- #10 current carrying conductors in a 2" conduit.
I checked into it and according to table 310.15 (B 3 a) which is the adjustment factors table, it reads that above 40 current carrying conductors must be reduced by 35% of its original ampicity.
According to table 310.15 ( B 16 ) a #10 THHN has a max ampicity of 40a, after reducing to 35% the #10 now has a ampicity of only 14A. These conductors are slated to be terminated on 20A circuit breakers.
I certainly see his installation as a violation.

Am I correct on this or am I misunderstanding the tables and the adjustment methods.
 
Thanks jumper, funny because when I showed the adjustment table to the guy doing the work he did think the table was stating what you reduce the ampicity by.
according to that logic than the more conductors in the conduit than the greater the ampicity gets.
 
You are using the tables correctly.

Those conductors cannot go on 20A breakers unless the loads are motors or such listed in 240.4(G).

It is possible that a 15A breaker could be used per 240.4(B) if the conditions are met.
 
jamesboy123 said:
one of the guys on the job are installing 42- #10 current carrying conductors in a 2" conduit.
I checked into it and according to table 310.15 (B 3 a) which is the adjustment factors table, it reads that above 40 current carrying conductors must be reduced by 35% of its original ampicity.
According to table 310.15 ( B 16 ) a #10 THHN has a max ampicity of 40a, after reducing to 35% the #10 now has a ampicity of only 14A. These conductors are slated to be terminated on 20A circuit breakers.
I certainly see his installation as a violation.

Am I correct on this or am I misunderstanding the tables and the adjustment methods.
Click to expand...
Maximum load you can connect to these conductors is 14 amps. You can protect such installation with 15 amp breaker as that is next size up. Motors, air conditioners, and such may allow even higher overcurrent device setting - but FLA x 1.25 or MCA will still be 14 amps max.

Such loads generally are limited to permanently connected loads or individual outlet circuits - a multioutlet circuit supplying receptacle outlets doesn't exactly have an assigned load, if you put it on a 15 or 20 amp breaker what is to keep you from plugging in more then 14 amps of load?
 
kwired said:
Maximum load you can connect to these conductors is 14 amps. You can protect such installation with 15 amp breaker as that is next size up. Motors, air conditioners, and such may allow even higher overcurrent device setting - but FLA x 1.25 or MCA will still be 14 amps max.

Such loads generally are limited to permanently connected loads or individual outlet circuits - a multioutlet circuit supplying receptacle outlets doesn't exactly have an assigned load, if you put it on a 15 or 20 amp breaker what is to keep you from plugging in more then 14 amps of load?
Click to expand...

240.4(B) does not allow the next size up OCPD for circuits serving multiple receptacles.
 
the conductors are all slated to be terminated on 20A circuit breakers and there is no deviating from that. If it passes inspection it will only be because the inspector does not pick up on the violation but certainly not because
the installation is correct.
Its actually a 42 circuit panel and he putting 21 hot legs and 21 neutrals in each 2" conduit, for a total of 42 circuits.
On top of this violation, all 84- #10 HRs are in a 18x18x6 pullbox where up to 42 - #12 guage MC cables will enter as the field branch circuits.
So the pull box will have 84- #10s and 126- # 12 conductors.
Not 100% positive but I don't think 210 conductors being aloud in a 18x18x6 pull box.
 
yes, its 21 circuits per 2" conduit. He is using 2 - 2" conduits.
I will to the table you listed, without even looking I am fairly certain that the pull box size is another violation.
Thanks for your replies
 
yes Jumper that is correct. 21 circuits in each conduit. 42 current carrying conductors in each conduit.
I did not mention the second conduit in my original as it was irrelevant at the time.
I guess things kind of evolved into mentioning it.
sorry for the confusion
 
jamesboy123 said:
the conductors are all slated to be terminated on 20A circuit breakers

21 hot legs and 21 neutrals in each 2" conduit, for a total of 42 circuits.

18x18x6 pullbox

So the pull box will have 84- #10s and 126- # 12 conductors.
Click to expand...

The #10 home run conductors are too small after derating (42*35%=14.7 amps) for the 20 amp circuits.
The pull box is more than large enough but may turn into a mess. (84*2.50)+(126*2.25)=493.5 cu in minimum, (18*18*6)=1944 cu in.
 
the pull box is a absolute mess. According to your calculations you are saying that all those wires could fit into a 8x8x8 pull box which is 512 ci. I did not even look at the table but I find it hard to believe that the NEC is saying
that 210 conductors ( 84 0f them being #10s) can enter and splice to one another and this leaves a safe work men like installation. And if the NEC is stating this to be true than they are horribly mistaken as to the space required to accomplish this task.
 
jumper said:
21 hots and 21 neutrals is 21 circuits.

The pull box size would be determined by 314.28.
Click to expand...

retirede said:
The way I read it, he has 2 - 2" conduits, each with 21 circuits for a total of 42 circuits.
Click to expand...

jumper said:
Oops. Darn little details.

Still 314.28 for sizing.
Click to expand...

Well phooey, not paying attention again. 314.28 is for #4 and larger, saw the 2" conduits and went to that section instead of 314.16.
 
Here's an 18X18 with about 2,000,000 conductors. :cool:

24106422747_b17b4bd322_m.jpg
 
Depending on the length of the circuits and the 2" conduits you may be able to take advantage of 310.15(A)2 Exception.
 
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