Protecting nm cables inside of emt

[Max Headroom]

Hi everybody, If I use 3-4 ft of EMT to protect my exposed NM cable from the back of my panel up into the roof framing (four 12/2 nm inside of 4ft of 1 1/4 EMT) do I still need to derate for more than three ccc. The top of the conduit would have a bushing and the bottom end makes up into an LB (existing) which goes into the back of the panel. Total cross section area of the four cables, if I figured correctly, would be 1.097 in sq, and the emt is 1.496 in sq so about 73.33% fill. Thanks for any help,

 

[infinity]

Since it's merely a sleeve there is no fill calculation needed. You will need to derating being that it is over 24" but with 8 CCC's you're derated ampacity will be 21 amps.

 

[LarryFine]

Yes, you must derate for eight CCCs.

 

[Max Headroom]

Since it's merely a sleeve there is no fill calculation needed. You will need to derating being that it is over 24" but with 8 CCC's you're derated ampacity will be 21 amps.

Thank you Infinity, the no fill requirement, is that in the NEC?

 

[LarryFine]

. . . you're derated ampacity will be 21 amps.

Even with NM cables' ratings?

 

[petersonra]

Since it's merely a sleeve there is no fill calculation needed. You will need to derating being that it is over 24" but with 8 CCC's you're derated ampacity will be 21 amps.

But you are still limited to 20 amps even if the temp detating comes out to 21 amps

 

[Max Headroom]

Even with NM cables' ratings?

Even with NM cables' ratings?

I have NM-B so I believe I can use the 90 degree column for derating as I have 20A breakers which keeps me in the 60 degree column? 334.80

 

[Max Headroom]

Since it's merely a sleeve there is no fill calculation needed. You will need to derating being that it is over 24" but with 8 CCC's you're derated ampacity will be 21 amps.

OK I think I found it, Chapter 9 Table 1 Note 2, it infers we don't need to consider conduit fill for sections of conduit used to protect exposed wiring and cable from physical damage.
Thanks everyone, have a great day

 

[tortuga]

Take a close look at 312.5(C) exception 1

 

[Max Headroom]

Take a close look at 312.5(C) exception 1

OK so 312.5(C) Exception No. 1, this enclosure is in a wood box on the outside of the garage, inside the garage on the back of the cabinet is an existing LB which I had planned to use for convenience but according to exception 1
Exception No. 1:
Cables with entirely nonmetallic sheaths shall be permitted to enter the top of a surface-mounted enclosure through one or more nonflexible raceways not less than 450 mm (18 in.) and not more than 3.0 m (10 ft) in length, provided all of the following conditions are met:

 

[infinity]

Take a close look at 312.5(C) exception 1

I figured that didn't apply.

 

[infinity]

I have NM-B so I believe I can use the 90 degree column for derating as I have 20A breakers which keeps me in the 60 degree column? 334.80

Yes you use 90° C ampacity for the basis of your derating.

 

[Max Headroom]

OK I have an idea I am going to move the EMT for him, it's running horizontally midway on a wall that he wants to cut a doorway into and it has the eight conductors mentioned earlier plus two 10awg on a dbl pole 30A, so I could move the EMT up and over the proposed doorway for the single pole circuits and then run some 10/3 mc for the double pole, problem solved

 

[tortuga]

I figured that didn't apply.

I presume 312.5(C) applies anytime a cable type wiring method is entering a panel ?
I just remember that section becasue its like something I trip over then forget and proceed to trip over it again and again.

 

[Max Headroom]

Take a close look at 312.5(C) exception 1

Are you referring to 312.5(C)(7) because if I am understanding that correctly then I would only be allowed 40% fill?

Where installed as conduit or tubing, the cable fill does not exceed the amount that would be permitted for complete conduit or tubing systems by Table 1 of Chapter 9 of this Code and all applicable notes thereto. Note 2 to the tables in Chapter 9 does not apply to this condition.

 

[tortuga]

Are you referring to 312.5(C)(7) because if I am understanding that correctly then I would only be allowed 40% fill?

Where installed as conduit or tubing, the cable fill does not exceed the amount that would be permitted for complete conduit or tubing systems by Table 1 of Chapter 9 of this Code and all applicable notes thereto. Note 2 to the tables in Chapter 9 does not apply to this condition.

Yes and you mentioned a LB going into the back of the panel not top of the panel.
We have had some long threads on 312.5(C) Exception, I think I am a repeat offender, I have many times used flex as a sleeve for NM cable into a panel.

 

[Max Headroom]

Yes and you mentioned a LB going into the back of the panel not top of the panel.
We have had some long threads on 312.5(C) Exception, I think I am a repeat offender, I have many times used flex as a sleeve for NM cable into a panel.

OK well this has definitely been good for me, the whole job was done years ago and is a mess, i just didn't want to add to the problem but now I have come up with a work around and I will not need to use NM cable, I'll probably use 3/4 EMT off the back of the cabinet for my 8ccc and then run a 10/3 mc for the one remaining 30A dbl pole circuit. Thank you all very much for your help!