Conduit fill

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  #1  
Old 01-03-06, 11:33 AM
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Conduit fill

An electrician and I ran some 1" flexible AL conduit from my main panel to what was going to be a subpanel. We underestimated the length and now I have a junction box where the conduit ends. We have three #2 AWG and one #8 (maybe 6, I forgot) in this 1" conduit. It was a tight fit but we were able to pull it.

To complete the job, I am splicing the cables in the J-box and then running a couple feet of AL flex to the sub. When I went to Home D for more cable, the guy who cut my cable said I needed larger conduit. He cut three short lengths of #2 and they wouldn't really fit in the "1. I ended up buying 1 1/4" flex conduit and a #4 ground.

When I checked the new #2 wire to the #2 wire that was in the 1", the brand was different but seemed to have thinner insulation. I am worried that the size differences will be a flag to the inspector. I checked the 2005 NEC and can't figure out the tables to determine the number of cables allowed in the size of conduit. More importantly, is it safe?
 
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  #2  
Old 01-03-06, 12:04 PM
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There are many different types of wire, and many different types of conduit. You have to know the exact type of each to know how many of what size wire fits in what size conduit. And your situation is one of those close ones where the type of wire and type of conduit make a difference.
 
  #3  
Old 01-04-06, 09:29 AM
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Above code

I will provide the entire printed description on the wire if that help. Basically, I bought it at HD, along with the AL 1" flexible conduit. The wire is 2 AWG, THHN (I think) stranded copper with a oil, gasoline, sunlight resistant jacket.

Maybe the bigger question is if I have to run another length of conduit, my new panel is going to run out of room for the conduit connections, so is there a better way of getting wire there?
 
  #4  
Old 01-04-06, 11:35 AM
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I'm going to assume that the type of conduit you have is FMC (Flexible Metal Conduit). I'm also going to assume that your THHN is dual-rated as THWN (otherwise, you ran the wrong wire if the conduit is underground).

40% of the cross-sectional area of 1" FMC is 0.327 square inches. #2 THHN has a cross sectional area of 0.1158 square inches. Three #2 have an area of 0.3428. I think you can see that we're already in trouble here, and I haven't even added in your grounding wire (of "I forgot" size).
 
  #5  
Old 01-04-06, 01:23 PM
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Pull more conduit?

Your assumptions are correct, sorry I wasn't clear. Since it seems unavoidable to run more conduit, I am thinking that I want to use the remaining 45 feet of 1.25" EMT conduit I have left.

My reasoning is that the larger the conduit attached to my panel, the better because I am running out of openings to fit the conduit. The only real access to the panel is from the top. The sides of the panel are surrounded by wood studs, so it isn't practical to attach conduit that way.

So if the top is the main way in for new circuits, is it better to run the larger conduit so I can fit more than just one #2 AWG?
 
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Old 01-04-06, 05:25 PM
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I would run the 11/4" there should be a knockout in the top of the panel.There should be knockouts in the bottom also
 
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Old 01-09-06, 10:15 AM
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NEC says different

Originally Posted by John Nelson
I'm going to assume that the type of conduit you have is FMC (Flexible Metal Conduit). I'm also going to assume that your THHN is dual-rated as THWN (otherwise, you ran the wrong wire if the conduit is underground).

40% of the cross-sectional area of 1" FMC is 0.327 square inches. #2 THHN has a cross sectional area of 0.1158 square inches. Three #2 have an area of 0.3428. I think you can see that we're already in trouble here, and I haven't even added in your grounding wire (of "I forgot" size).
John,
When faced with all the work of pulling more conduit and wire, I found in the 2005 NEC, Annex C, a table of THHN wire and EMT conduit. Three #2 wires are allowed in 1 inch EMT. I have not read all the pages in the code so I am wondering what you think.
 
  #8  
Old 01-09-06, 11:35 AM
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That must be difference in rounding, because my calculation comes up to 40.2% fill for three #2 THHN in 1" EMT; 40% is the maximum allowed fill. Even if this is allowed, it still leaves no room for the ground.
 
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Old 01-09-06, 12:45 PM
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THHN or THHW

I will double check, but to John Nelson's point that if the cable is rated for both THHN and THHW, then it is thicker? I think I remember the cable saying "THHN OR THHW" and some other letters as well.
 
  #10  
Old 01-09-06, 02:21 PM
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I found in the 2005 NEC, Annex C, a table of THHN wire and EMT conduit. Three #2 wires are allowed in 1 inch EMT.
I was hoping you wouldn't notice that. I also saw that entry in the Appendix C table, but then I did the calculation using the Chapter 9 information and found that three #2 was a bit too much. I can't explain why Chapter 9 and Appendix C seem to disagree. I hope somebody else will double-check my Chapter 9 math and see if they know why it disagrees with Appendix C.

However, in either case, this is a real close situation. So close, that, as was pointed out, there is certainly no room for that grounding wire.
 
  #11  
Old 01-09-06, 03:19 PM
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Originally Posted by John Nelson
However, in either case, this is a real close situation. So close, that, as was pointed out, there is certainly no room for that grounding wire.
Since these cables feed my 100 Amp subpanel, which will become the center for all my wiring as I rewire my AL wired house, is it a good idea to remove the ground wire from the conduit and run it next to the conduit (which is runs above the master bedroom ceiling and into the attic and then drops to the sub)?
 
  #12  
Old 01-09-06, 04:24 PM
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Not only a bad idea, it's not allowed by code.
 
  #13  
Old 01-09-06, 05:08 PM
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What do you suggest?

Originally Posted by John Nelson
Not only a bad idea, it's not allowed by code.
Ok, so I won't just pull the ground wire out and lay it next to the conduit. How about running it in another EMT conduit, a separte one from the conduit that has my three #2 wires? (This ground wire is insulated, rated THHN).
 
  #14  
Old 01-09-06, 05:30 PM
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Sorry, still not allowed by code. All four wires must be in the same conduit.
 
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Old 01-09-06, 07:47 PM
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Argggghh!

Originally Posted by John Nelson
Sorry, still not allowed by code. All four wires must be in the same conduit.
John, Please provide the code reference. I am dying over this!
 
  #16  
Old 01-09-06, 08:36 PM
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Reference the 2005 NEC:

"300.3(B) Conductors of the Same Circuit All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1) through (B)(4)."

If you follow all the links and read all the exceptions, I believe that you will find that none of them apply to your situation. This rationale of this rule is to reduce inductive heating and to avoid increases in overall circuit impedance.
 
  #17  
Old 01-09-06, 09:20 PM
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Above code

Ok, first off, I understand that everyone is trying to help. I want a safer house, so I am putting in the subpanel and its feeders to make the re-wire of my AL wired house easier. I choose #2 wire when #4 or #3 would have worked for my 100 Amp sub. The bigger the wire, the less it will heat. Electrician and I checked the tables before we bought and when I asked him about the ground wire he said they don't count it. I should have stopped him there. However, the 1.25" EMT allows FIVE #2 wires.

So here I am, wondering why it isn't safe to run a loose insulated ground wire behind a cathedral ceiling and into the attic to connect to the sub?
 
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Old 01-10-06, 08:29 PM
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I'm actually wondering the same thing. I would like to run the wires from my meter panel with the main breaker to my load center. I have to run three 00 wires and a ground - which will fit in a 1.5" conduit and I wouldn't have too much trouble doing it but it would certainly be much easier to just run the wires bundled together in the open air. I have a feeling part of it has to do with there not being a sheath around the wires. The other part of it is that code probably requires conduit for loose wires regardless of whether they are bundled together with zip ties or clamps or whatnot.

Steve
 
  #19  
Old 01-10-06, 08:44 PM
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Tyger, the answer is heavily entangled in physics. But the bottom line is that in the event of a fault, the breaker will trip faster if the grounding wire is in the same conduit as the conductors. It has to do with the magnetic fields created by flowing current.

Bob/Steve/Tomahawk, your situation is different. The physics above only apply to wires in metallic conduit. All wires need physical protection, and some form of conduit is just one way of doing it.
 
  #20  
Old 01-10-06, 10:31 PM
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Originally Posted by John Nelson
Bob/Steve/Tomahawk, your situation is different. The physics above only apply to wires in metallic conduit. All wires need physical protection, and some form of conduit is just one way of doing it.
John, I think you are right that wiring needs some kind of protection. Does drywall count? I somehow doubt it. I would guess that NEC says somewhere that conduit is needed for individual wires. Can anyone cite the reference?

And it is...

Steve

Bob L. is just a funny name (say it fast) and Thawk is just a job. Just a fun job.
 
  #21  
Old 01-11-06, 07:21 AM
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Cool, I took a year of physics in college

Originally Posted by John Nelson
Tyger, the answer is heavily entangled in physics. But the bottom line is that in the event of a fault, the breaker will trip faster if the grounding wire is in the same conduit as the conductors. It has to do with the magnetic fields created by flowing current.
I am aware of magnetic fields created by flowing current. However, in the event of a fault, how those minor fields could cause the breaker trip faster is beyond me so I would really appreciate an explanation or reference.
 
  #22  
Old 01-11-06, 08:52 AM
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I have a feeling the magnetic fields thing is smoke and mirrors but I do know that code says all wires and the associated ground for a circuit have to run in the same conduit.

Steve
 
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Old 01-11-06, 09:02 AM
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Whether there is any validity to the em (electromagnetic) radiation theory or not, as it relates to a ground conductor, is a moot point. It is not allowed by code. The theory certainly is very applicable when it comes to current carrying conductors.
 
  #24  
Old 01-11-06, 01:22 PM
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In normal conditions, the fields produced by wires are very small. But in a fault condition, you may have thousands of amps flowing (briefly, we hope). The field effects are much greater.
 
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Old 01-11-06, 03:46 PM
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Originally Posted by John Nelson
I hope somebody else will double-check my Chapter 9 math and see if they know why it disagrees with Appendix C.


Link to error Note NEC 2005.
http://www.electrician.com/rfcalculator_fix.htm


Link to Raceway calculator.
http://www.electrician.com/calculato...calc_rev3a.htm
 
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Old 01-11-06, 08:26 PM
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Hey, thanks a lot GWIZ.
 
  #27  
Old 01-12-06, 09:54 AM
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Follow up

I have decided to pull more 1.25" conduit. I am stubborn, I admit, so I really didn't want to do this. I have the 1" conduit completely in place with the wires. That said is there any advice on the situation?
 
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