Conduit Fill?

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Old 05-15-10, 03:39 PM
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Conduit Fill?

I have been using the chart at Conduit Fill Chart but I have noticed some differences from what is quoted in the forum. For instance it says 9 #12 in 1/2" EMT but I have seen 7 quoted in the forum. Is this chart wrong or is there some factor I'm missing in using the chart?

P.S. Yes, if you read the thread I responded to earlier I said 10 but my must of crossed. That was just a misread on my part. I'm asking because this is one of my resources when I answer questions and if it isn't correct I'll look elswhere.
 
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Old 05-15-10, 03:50 PM
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Your chart is referring to total wires in conduit if im not mistaking and the NEC is current carrying conductors in a conduit.

In a 1/2 conduit I would pull 4 max circuits which would be 4 hots and 2 neutrals, plus a ground. At 4 you will have to start derating the wire. I am not 100% sure but this is how I would do it and the NEC does state 7 wires 12awg but I cant find a direct reference to CCCs, I am just quoting from experience. I would like to know a definite answer and article if anyone could provide that.

P>S> on the link you provided it states right below that chart
Above information referenced from tables C1, C4, and C8 of the 1996 NEC
The codes change every 3 years and that is likely outdated.

P.S. http://www.techlicensing.com/examples.html

This shines a little light on the subject but it still really does not pinpoint it for me.
I do not agree with this guy on 9 CCCs in a 1/2 conduit though. Thats insane... My foreman told me 4 is max period in any conduit and you derate at 40% after that. That maybe his preference though. Im actually glad this came up in the forums.
 

Last edited by SilverTattoo; 05-15-10 at 04:20 PM. Reason: i wanted to add something,
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Old 05-15-10, 04:24 PM
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The NEC conduit fill charts are for the total number of conductors allowed in a specific conduit size and material. Even grounding conductors take up space and must be allowed for when determining conduit fill.

I did nnot check the chart from the link against my code book. There will also be differences based on conduit material and insulation types used.
 
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Old 05-15-10, 04:46 PM
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Yes true. The grounds do count. How we do it is you count all the grounds are 1, isolated grounds are separate, count hots and neutrals per wire.

Example in a 1/2 conduit (with THHN wire) 3 circuits, 1 neutral, 2 grounds, and 1 isolated ground = a 6 wire count for fill. (yes you only need one ground that was just an example.

Not to mention if you run 9 wires is gonna be a mother to pull in a 1/2 conduit! Also if all 9 are CCCs, where are the ground(s).....? This is something i have never really found a definite answer on and if it exist I would love to know and have the article for it. I was talking just Friday about this at work.. We all had a different answer and no1 could prove it via NEC.
 
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Old 05-15-10, 04:53 PM
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Using 1/2" EMT with a limit of 9 #12's, you could have any combination of hots, neutrals and grounds as long as they add up to 9 or less.

Derating for number of conductors is different.
 
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Old 05-15-10, 04:55 PM
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Originally Posted by SilverTattoo View Post
Not to mention if you run 9 wires is gonna be a mother to pull in a 1/2 conduit! Also if all 9 are CCCs, where are the ground(s).....? This is something i have never really found a definite answer on and if it exist I would love to know and have the article for it. I was talking just Friday about this at work.. We all had a different answer and no1 could prove it via NEC.
EMT you do not need a grounding conductor. The conduit is the ground.

We quite commonly will pull in 8 CCC. 6 hots and 2 neutrals. (Neutrals are concidered current carrying) AKA two - three phase mulitwires. With 1/2" EMT and THHN wires derateing is not an issue. THHN is rated at 30 amps. At 70% you still come out to 21 amps so you are still above what is allowed for #12 THHN

Ray - Your chart is correct. I go by the NEC charts in the back of the book.
 
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Old 05-15-10, 04:59 PM
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Thanks all. Just wanted to be sure I wasn't giving people wrong answers.
 
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Old 05-15-10, 05:09 PM
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EMT you do not need a grounding conductor. The conduit is the ground.

We quite commonly will pull in 8 CCC. 6 hots and 2 neutrals. (Neutrals are concidered current carrying) AKA two - three phase mulitwires. With 1/2" EMT and THHN wires derateing is not an issue. THHN is rated at 30 amps. At 70% you still come out to 21 amps so you are still above what is allowed for #12 THHN

Ray - Your chart is correct. I go by the NEC charts in the back of the book.
Thats way off and not true at all. Yea the conduit is grounded but you still have to pull in a ground wire... Thats common since.
No inspector I know will ever pass that!

With 1/2" EMT and THHN wires derateing is not an issue. THHN is rated at 30 amps. At 70% you still come out to 21 amps so you are still above what is allowed for #12 THHN
Wrong here again. derating is a BIG issue. Those wire will heat up and then you got a real issue on your hands. Read the code again.

Using 1/2" EMT with a limit of 9 #12's, you could have any combination of hots, neutrals and grounds as long as they add up to 9 or less.

Derating for number of conductors is different.
This is also way off and wrong. Apparently you guys are residential. Thats way!!!!!!!! overloaded on that conduit. It does matter with CCCs thats why its code and thats why you derate to keep the wire from burning up. The more current in the conduit (CCC wires ) the hotter they get.

NEC Article 310.15(2)(A)

Where the number of current - carrying conductors in a raceway(conduit) exceeds 3 , the ampacity of EACH CONDUCTOR SHALL BE REDUCED!!


Table 310.15(B)(2) Adjustments for wire temperature
 
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Old 05-15-10, 05:22 PM
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Originally Posted by SilverTattoo View Post
Thats way off and not true at all. Yea the conduit is grounded but you still have to pull in a ground wire... Thats common since.
No inspector I know will ever pass that!
The inspector would be incorrect not to pass it. Article 250.118 has a list of acceptable EGCs.



Originally Posted by SilverTattoo View Post
Wrong here again. derating is a BIG issue. Those wire will heat up and then you got a real issue on your hands. Read the code again.
With 1/2" EMT and THHN wires derateing is not an issue. THHN is rated at 30 amps. At 70% you still come out to 21 amps so you are still above what is allowed for #12 THHN

Derating is an issue, but if you look at the ampacity tables you are still above the allowable ampacity limit for #12 conductors.



Originally Posted by SilverTattoo View Post
This is also way off and wrong. Apparently you guys are residential. Thats way!!!!!!!! overloaded on that conduit. It does matter with CCCs thats why its code and thats why you derate to keep the wire from burning up. The more current in the conduit (CCC wires ) the hotter they get.
I will stand by what I posted before. The conduit fill charts simply tell how many conductors will fit in the conduit. If you are over a certain number of CCC in the allowable number of conductors, derating factors come into play.

NEC Article 310.15(2)(A)

[/quote]
 
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Old 05-15-10, 05:24 PM
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Originally Posted by SilverTattoo View Post
Thats way off and not true at all. Yea the conduit is grounded but you still have to pull in a ground wire... Thats common since.
No inspector I know will ever pass that!
You must be confusing flex conduit for EMT. We run thousands of feet of EMT a year on commercial jobs and never need to pull a ground. Around here the only time we have to run a ground wire is for an isolated ground or HCF. This is not just the new stuff we run, but everything we encounter on remodel jobs as well.

BTW - (2005) 358.60 Grounding. EMT shall be permitted as an equipment grounding conductor.

Originally Posted by SilverTattoo View Post
Wrong here again. derating is a BIG issue. Those wire will heat up and then you got a real issue on your hands. Read the code again.

This is also way off and wrong. Apparently you guys are residential. Thats way!!!!!!!! overloaded on that conduit. It does matter with CCCs thats why its code and thats why you derate to keep the wire from burning up. The more current in the conduit (CCC wires ) the hotter they get.
Yes, it is an issue but with 1/2" pipe the issue is moot. OK, lets do the math again. THHN is rated at 30 amps per 310.16. You pull in 8 wires. 6 hots and 2 neutrals. 30 x .70 (70% per table 310.15(B)(2) ) = 21 amps. Per 240.4(D) #12 max over current device is 20 amps. Each conductor is rated at 30 amps. Each conductor is reduced to 21 amps.
 

Last edited by Tolyn Ironhand; 05-15-10 at 06:24 PM.
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Old 05-15-10, 05:25 PM
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Those who cant, teach.

I will let you think what you will. What does NEC know anyhow...
 
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Old 05-15-10, 05:27 PM
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Thats way off and not true at all. Yea the conduit is grounded but you still have to pull in a ground wire... Thats common since.
No inspector I know will ever pass that!
Local codes prevail over NEC. NEC doesn't require a grounding conductor with EMT, but I prefer one.
 
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Old 05-15-10, 05:31 PM
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Originally Posted by SilverTattoo View Post
Those who cant, teach.

I will let you think what you will. What does NEC know anyhow...
Scott and I have both backed up our posts with the applicable NEC Articles.

As far as what the NEC knows, it is a consensus document written by people involved in different aspects of the trade. It is the rule book if you are going to play in the game and it needs to be followed. I am sorry you seem to disagree.

BTW, I don't teach, but do understand that learning is a continuous process.
 
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Old 05-15-10, 07:03 PM
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Nec is the MINIMAL requirements for electrical safety.. 2nd we are all continuously learning. 3rd any self respecting electrician pulls in a device ground. Conduit will and does pull apart and should not be 100% relied upon.. I guess like I said in the other post its work ethics. I don't like to cut corners especially safety!
 
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Old 05-15-10, 07:22 PM
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ok this part

Yes, it is an issue but with 1/2" pipe the issue is moot. OK, lets do the math again. THHN is rated at 30 amps per 310.16. You pull in 8 wires. 6 hots and 2 neutrals. 30 x .70 (70% per table 310.15(B)(2) ) = 21 amps. Per 240.4(D) #12 max over current device is 20 amps. Each conductor is rated at 30 amps. Each conductor is reduced to 21 amps.
where is the 30 amps coming from? #12 is good for 20 amps.
 
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Old 05-15-10, 07:37 PM
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Table 310.16 lists #12 THHN at 30 amps in the 90 degree column. The asterisk behind the wire size calls out 240.4(D) which limits #12 to 20 amps.

The 90 degree column is used as the starting point for temperature and number of conductors in a raceway derating. However, the ampacity cannot be more than 240.4(D) allows.
 
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Old 05-15-10, 07:39 PM
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Originally Posted by SilverTattoo View Post
ok this part
where is the 30 amps coming from? #12 is good for 20 amps.
NEC Table 310.16 (2005) Allowable ampacities. This is the table where you start derateing. Then go to table 310.15(B)(a) for adjustment factors for more than three current carrying conductors. Note the heading above the percentages that states "Percent of values in tables 310.16 through 310.19..."

Note: The reason I am quoting from 2005 code is because the 2008 book is in the truck. I can quote from that one too if you wish but it is unnecessary as these codes have unchanged for many years.

I really should check if PCboss posted the same time I do.
 
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Old 05-15-10, 07:55 PM
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I was looking at the wrong chart... I was looking at ENT... Not EMT... I appologize for that. So to the OP yea that chart is right. NEC table C.1....not C.2..
So yea 1/2 EMT conduit is 12awg 9 wires.
 

Last edited by pcboss; 05-16-10 at 02:08 AM. Reason: spelling
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Old 05-15-10, 09:04 PM
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Hey silver don't be hard on yourself. Earlier today in another thread I quoted from IMC instead of EMT.
 
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Old 05-15-10, 09:23 PM
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Yea true, though I should of known better than that. I was sitting here thinking "7 dont sound right but this is what im reading" and low and behold I was reading the wrong page... LOL o well, its been a long day.
 
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Old 05-15-10, 10:07 PM
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Originally Posted by SilverTattoo View Post
I was looking at the wrong chart... I was looking at ENT... Not EMT... I appologize for that. So to the OP yea that chart is right. NEC table C.1....not C.2..
So yea 1/2 EMT conduit is 12awg 9 wires.
Silver .,

As long the OP did mention THHN/THWN conductors that is correct but if you used or it have TWN or others then the bet is off it will change the figures a bit espcally with older conductors I know it can be pain in arse with few diffrent conductor materals in there.

but the derating rules still stand not only in NEC codes in USA but ditto in French electrical codes it almost the excat the same answer as well but at diffrent tempture and conductor rating.

Merci,Marc
 

Last edited by pcboss; 05-16-10 at 02:09 AM.
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