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Old 11-06-2008, 06:08 PM   #1
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ENT - Flexiable


HI;

Can anyone tell me where you are generally allowed to use the flexiable ENT? Can it be used with thhn in the same places that NM would generally be able to be used? Or are there additional rules are where you can and can not use it?

I can't find a fill chart for flexiable ENT, are the fill amounts similar to that of ENT?

I have a couple projects that I have THHN for that I would really like to use, but they are in locations that are very difficult to run solid EMT.

Thanks
Jamie

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Last edited by jamiedolan; 11-06-2008 at 06:09 PM. Reason: added info.
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Old 11-06-2008, 06:28 PM   #2
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ENT - Flexiable


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Originally Posted by jamiedolan View Post
HI;

Can anyone tell me where you are generally allowed to use the flexiable ENT? Can it be used with thhn in the same places that NM would generally be able to be used? Or are there additional rules are where you can and can not use it?

I can't find a fill chart for flexiable ENT, are the fill amounts similar to that of ENT?

I have a couple projects that I have THHN for that I would really like to use, but they are in locations that are very difficult to run solid EMT.

Thanks
Jamie
You can use it anywhere that romex is used practically. You can't use it exposed above the third floor of a building, or for direct burial in earth, or at voltages over 600 V. The fill rules are the same as any conduit. That is, over two conductors, no more than 40% of the cross-sectional area can be filled.

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Old 11-06-2008, 07:00 PM   #3
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ENT - Flexiable


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Originally Posted by InPhase277 View Post
You can use it anywhere that romex is used practically. You can't use it exposed above the third floor of a building, or for direct burial in earth, or at voltages over 600 V. The fill rules are the same as any conduit. That is, over two conductors, no more than 40% of the cross-sectional area can be filled.
Thank you.

I am looking at this fill chart:

http://infohost.nmt.edu/~armiller/ho...onduitsize.htm

It says for example, that 3/4" can hold 5 - #8 wires, would that be the proper capicity, or would the real capicity only be 40% of that?

Thanks.
Jamie
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Old 11-06-2008, 07:16 PM   #4
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ENT - Flexiable


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Originally Posted by jamiedolan View Post
Thank you.

I am looking at this fill chart:

http://infohost.nmt.edu/~armiller/homerepair/conduitsize.htm

It says for example, that 3/4" can hold 5 - #8 wires, would that be the proper capicity, or would the real capicity only be 40% of that?

Thanks.
Jamie
Well, I'll let you do the math, 'cause it'll help you learn better. For THHN, the area of the conductors, in square inches, is as follows:

#14: 0.0097
#12: 0.0133
#10: 0.0211
#8: 0.0366

For ENT conduit, the area is as follows:

1/2": 0.246
3/4": 0.454
1": 0.785

At 40%:

1/2": 0.099
3/4": 0.181
1": 0.314
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Old 11-06-2008, 07:30 PM   #5
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Originally Posted by InPhase277 View Post
Well, I'll let you do the math, 'cause it'll help you learn better. For THHN, the area of the conductors, in square inches, is as follows:

#14: 0.0097
#12: 0.0133
#10: 0.0211
#8: 0.0366

For ENT conduit, the area is as follows:

1/2": 0.246
3/4": 0.454
1": 0.785

At 40%:

1/2": 0.099
3/4": 0.181
1": 0.314
Thank You. I am comming up with numbers that are very close to the number in that chart ( http://infohost.nmt.edu/~armiller/ho...onduitsize.htm ) for larger gage wire. However for smaller wire, like 14 gage in 1 inch, when I run numbers based on what you gave me, I come up with 32 - 14 gage wires in a 1" conduit at 40%. (Chart says 39 - so we have a 7 wire difference) :-)

Am I doing something wrong in my calculations or are there other variables that are causing my answer to be different than what I see in that chart?

Thanks for teaching me how to do the calculations.

Jamie
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Old 11-06-2008, 07:46 PM   #6
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Originally Posted by jamiedolan View Post
Thank You. I am comming up with numbers that are very close to the number in that chart ( http://infohost.nmt.edu/~armiller/homerepair/conduitsize.htm ) for larger gage wire. However for smaller wire, like 14 gage in 1 inch, when I run numbers based on what you gave me, I come up with 32 - 14 gage wires in a 1" conduit at 40%. (Chart says 39 - so we have a 7 wire difference) :-)

Am I doing something wrong in my calculations or are there other variables that are causing my answer to be different than what I see in that chart?

Thanks for teaching me how to do the calculations.

Jamie
No, you are right. 32 is the limit. The chart is just wrong. Now, when you go over 3 current-carrying conductors, you have to begin derating the ampacity. Table 310.15(B)(2)(a) shows the adjustment factors.

4-6 conductors : 80%
7-9 : 70%
10-20 : 50%
21-30 : 45%

Grounds aren't current-carrying. Neutrals in single-phase multiwire circuits aren't current-carrying, except when feeding discharge lighting.
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Old 11-07-2008, 12:50 AM   #7
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Originally Posted by InPhase277 View Post
No, you are right. 32 is the limit. The chart is just wrong. Now, when you go over 3 current-carrying conductors, you have to begin derating the ampacity. Table 310.15(B)(2)(a) shows the adjustment factors.

4-6 conductors : 80%
7-9 : 70%
10-20 : 50%
21-30 : 45%

Grounds aren't current-carrying. Neutrals in single-phase multiwire circuits aren't current-carrying, except when feeding discharge lighting.
So if I decided to run 5 circuits of thhn through 1 condit to my kitchen, I would have to cut there capicity in half? So my 12 gage wire would only be good for a 10A load?

So if I even run 2 12 gage circuits in a conduit together, then, I need to rerate it by %80, so that means that I can only use each of the circuits for 15A even thought they are 12 gage wires?

Jamie
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Old 11-07-2008, 12:59 PM   #8
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Originally Posted by jamiedolan View Post
So if I decided to run 5 circuits of thhn through 1 condit to my kitchen, I would have to cut there capicity in half? So my 12 gage wire would only be good for a 10A load?

So if I even run 2 12 gage circuits in a conduit together, then, I need to rerate it by %80, so that means that I can only use each of the circuits for 15A even thought they are 12 gage wires?

Jamie
When derating conductors, we use the 90 degree rating of the conductor. So for #12 THHN, that is 30 A. For #10 it is 40 A. The ampacity of a circuit is determined after all adjustment factors are applied. So, if you have, let's say, 8-#12 THHNs in a conduit, then we are required to derate them to 70%. Starting at 30 A, we see that the conductor will derate to 21 A. So, we can still use a 20 A breaker. With more fill, we have to up the size to #10.

Now, the Code allows us to go to the next highest breaker size if we end up with an odd ball ampacity. So if you derate, and end up with 17 A, you can still use a 20 A breaker.
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Old 11-07-2008, 01:22 PM   #9
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Originally Posted by InPhase277 View Post
When derating conductors, we use the 90 degree rating of the conductor. So for #12 THHN, that is 30 A. For #10 it is 40 A. The ampacity of a circuit is determined after all adjustment factors are applied. So, if you have, let's say, 8-#12 THHNs in a conduit, then we are required to derate them to 70%. Starting at 30 A, we see that the conductor will derate to 21 A. So, we can still use a 20 A breaker. With more fill, we have to up the size to #10.

Now, the Code allows us to go to the next highest breaker size if we end up with an odd ball ampacity. So if you derate, and end up with 17 A, you can still use a 20 A breaker.
So depending on the factors invloved in the derating calculation I might be able to pull 5 20A circuits in 1 conduit with 12gage. - I assume these charts are found in the NEC guide so I could calculate exactly how much I need to derate them. Running 1 or 2 pieces of ENT to my attic above my kitchen sounds much easier than running 10 pieces of NM to do the same thing.

So if #12 starts at 30, if it is the only thing is the conduit, (I think you mentioned you have to derate when you have 3 or more), can you actually run a #12 at 30A?

Jamie
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Old 11-07-2008, 01:32 PM   #10
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ENT - Flexiable


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Originally Posted by jamiedolan View Post
So depending on the factors invloved in the derating calculation I might be able to pull 5 20A circuits in 1 conduit with 12gage. - I assume these charts are found in the NEC guide so I could calculate exactly how much I need to derate them. Running 1 or 2 pieces of ENT to my attic above my kitchen sounds much easier than running 10 pieces of NM to do the same thing.
If you have 5 circuits, that's 10 current-carrying conductors, and one ground. So derate appropriately.

Quote:
So if #12 starts at 30, if it is the only thing is the conduit, (I think you mentioned you have to derate when you have 3 or more), can you actually run a #12 at 30A?

Jamie
Only under a very narrow set of conditions can #12 be used on a 30 A circuit. And these are only met with motors and refrigeration equipment, generally. So, in general, no. #12 is limited to a maximum of 20 A in almost every situation likely to be encountered in a residence.

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