# 3/4 emt maximum cc in conduit.



## g20broo

The code can be confusing. 
Take the tables in NEC annex b & c - a 3/4 emt conduit is allowed to have approx 20 # 12 thhn wires in the conduit with 3 being current carrying.
But table 310-15 says that if there is 4-6 current carrying that has to be reduced to 80% ampacity capacity. 
Now of course who is going to actually put 20 in a 3/4" conduit? 
So according to 310.16 #12 thhn is rated at 30 amp. It just has to be breakered at no more than 20 amps. My land is there a better way of stating this in a more simplified manner? If I'm wrong please correct me. But this is how I read it. Anyone like to give any feedback on this?


----------



## BBQ

Not really a simple answer to this, there are many steps involved in this.

If you want to put more than 3 current carrying conductors in a raceway there will be calculations that will need to be done.


----------



## John

Lets say you install 6 #12 current carrying conductors in 3/4 conduit...what size breakers would you use?


----------



## 480sparky

John said:


> Lets say you install 6 #12 current carrying conductors in 3/4 conduit...what size breakers would you use?


#12 what?......


----------



## don_resqcapt19

In general, with 15 and 20 amp circuits as long as you have less than 10 current carrying conductors, there is no real issue. Once you have 10 or more, you can no longer use #12 on a 20 amp OCPD. (there are conditions where this general comment does not apply)


----------



## John

480sparky said:


> #12 what?......


#12 AWG THNN stranded for all concerned readers, but for you.....corn cobbs


----------



## John

480sparky said:


> #12 what?......


Now that the technical details are ironed out.....:whistling2:



John said:


> Lets say you install 6 #12 current carrying conductors in 3/4 conduit...what size breakers would you use?



Back to my question for the OP.


----------



## brian john

John said:


> #, but for you.....*corn cobbs*


That is a riot:laughing:


----------



## Celtic

Its like rocket surgery....only completely different.


----------



## BBQ

John said:


> Lets say you install 6 #12 current carrying conductors in 3/4 conduit...what size breakers would you use?


I would use a 120 amp breaker because 6 conductors x 20 amps each is 120 amps.

Of course I am kind of a hack. :jester:


----------



## nolabama

Celtic said:


> Its like rocket surgery....only completely different.


Similar to brain science ? Is my quote still the same??


----------



## Celtic

nolabama said:


> Similar to brain science ? Is my quote still the same??



Exactly the same.



....but different.


----------



## John

BBQ said:


> I would use a 120 amp breaker because 6 conductors x 20 amps each is 120 amps.
> 
> Of course I am kind of a hack. :jester:


I will see your 120 amp hack and raise you a 60 amp hack.:blink::thumbup1:


How about three 30amp tandom circuit breakers for a total of 180 amps and screw the code and derating.:jester::jester:


----------



## 480sparky

brian john said:


> That is a riot:laughing:


Specially when he can't spell it right.


----------



## g20broo

*Voltage drop calculations*

Is there a general rule in the trade for voltage drop when you have to just go to the next larger wire size as far as conduit run length? 

I undersstand that you do have the long voltage drop formula that give you the amount of drop. But like alot of things in the trade it seems to be just how the old school electricians just did it. X amount of feet and they just went to the next size larger wire. Any feedback on this topic?


----------



## Celtic

g20broo said:


> .... it seems to be just how the old school electricians just did it. X amount of feet and they just went to the next size larger wire. Any feedback on this topic?


I didn't know there was a school for old electricians, I thought they just knew everything magically.


----------



## stars13bars2

John said:


> Lets say you install 6 #12 current carrying conductors in 3/4 conduit...what size breakers would you use?


well you could go as high as a 150 amp breaker  depending on the situation.


----------



## g20broo

I can see this is going no where! I'm not sure I'm at the right forum!


----------



## Dennis Alwon

On the opening post I want to make sure you understand that the 80% is not the capacity of the 3/4" conduit but of the ampacity of the conductor. Thus a 12 wire at 75C is rated 25 amps so if you have 4-6 conductors then you must derate the 25 amps by 80%= 20 amps. If you have 20 CCC then you must derate 50% or 12.5 amps.


----------



## Dennis Alwon

The NEC does not req. VD calculations except for fire pumps. Generally I use an *online calculator* that bases it on 3%


----------



## John

John said:


> Lets say you install 6 #12 current carrying conductors in 3/4 conduit...what size breakers would you use?





Dennis Alwon said:


> On the opening post I want to make sure you understand that the 80% is not the capacity of the 3/4" conduit but of the ampacity of the conductor. Thus a 12 wire at 75C is rated 25 amps so if you have 4-6 conductors then you must derate the 25 amps by 80%= 20 amps. If you have 20 CCC then you must derate 50% or 12.5 amps.


Why is it no one will answer a question without pegging out the BS meter first?:no:


----------



## Celtic

John said:


> Why is it no one will answer a question without pegging out the BS meter first?:no:


I think it has something to do with corn cobbs :thumbup:


----------



## Electrician343

g20broo said:


> The code can be confusing.
> Take the tables in NEC annex b & c - a 3/4 emt conduit is allowed to have approx 20 # 12 thhn wires in the conduit with 3 being current carrying.
> But table 310-15 says that if there is 4-6 current carrying that has to be reduced to 80% ampacity capacity.
> Now of course who is going to actually put 20 in a 3/4" conduit?
> So according to 310.16 #12 thhn is rated at 30 amp. It just has to be breakered at no more than 20 amps. My land is there a better way of stating this in a more simplified manner? If I'm wrong please correct me. But this is how I read it. Anyone like to give any feedback on this?


derate.


----------



## frenchelectrican

Celtic said:


> I think it has something to do with corn cobbs :thumbup:


I going have to remember that word for a while :whistling2:

But what size dammed corn cobs ?? short cobs or long cobs ??

Merci,
Marc


----------



## sarness

And stranded or solid?


----------



## ChrisH8802

John said:


> #12 AWG THNN stranded for all concerned readers, but for you.....corn cobbs





brian john said:


> That is a riot:laughing:



i wanna be there when he pulls corn cobs into a 3/4'' conduit


----------



## 480sparky

frenchelectrican said:


> I going have to remember that word for a while :whistling2:
> 
> But what size dammed corn cobs ?? short cobs or long cobs ??
> 
> Merci,
> Marc


Um, it's not the length of the cob that's a factor..... It's the cmil. :O


----------



## frenchelectrican

480sparky said:


> Um, it's not the length of the cob that's a factor..... It's the cmil. :O


MDR ! I know you will say that one.

Merci,
Marc


----------

