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Old 02-26-2009, 07:43 PM   #1
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24" conduit rule derrating does not apply


Question on the 24" derating rule to make sure I understand it correctly.

If I ran this setup my understanding is that I would not derate regardless of the number of conductors.

12" of conduit from panel to LR
24" of conduit from LR to junction box

If I understand this correctly, This would allow me to avoid that last difficult bend to my panel for multiple emt runs.

So could you layout a whole panel so it just has one or two large conduits going out the top to ceiling mounted jboxes (with less than 24" between jboxes/conduit bodies to the ceiling boxes)?

Thanks
Jamie

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Old 02-26-2009, 08:17 PM   #2
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24" conduit rule derrating does not apply


Up here in Canada if the wire is in pipe you have to derate after 3 current carrying wires. It does not matter if the pipe is 12" long or 120' feet long.

There is a rule that states if wires(i.e nmd90) are grouped together for a certain distance then you have to derate those wires. This may be what your thinking.

Your idea about a junction box up high and conduit running from that to the panel is a great idea in my opnion. I did that in my house and ran 3 1" pipes between the box and the panel.

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Old 02-26-2009, 09:41 PM   #3
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24" conduit rule derrating does not apply


HI;

310.15 2 (a) is where I read this:

Exception No.3: Derating factors shall not apply to con
ductors in nipples having a length not exceeding 600 mm
(24 in.).

Jamie
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Old 02-27-2009, 09:20 AM   #4
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24" conduit rule derrating does not apply


You're almost correct. If you had a nipple 24" or less going from the panel to a j-box then you wouldn't have to derate.

However a conduit body doesn't "break" the conduit run, so if you are going from panel-12" - LR - 24" - J-box, you do not have a nipple of 24" or less. You have a conduit run of 36" + whatever the length of the LR is, and you will be subject to the rules of conduit fill and derating.
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Old 02-27-2009, 09:32 AM   #5
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24" conduit rule derrating does not apply


Jamie, I agree that what you describe is actually 36", not 24. But if you have a 24" nipple, not only does derating not apply, but according to Chaper 9 Note 4, you can fill up to 60% of the cross-sectional area.
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Old 02-27-2009, 09:55 AM   #6
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24" conduit rule derrating does not apply


Quote:
Originally Posted by EBFD6 View Post
You're almost correct. If you had a nipple 24" or less going from the panel to a j-box then you wouldn't have to derate.

However a conduit body doesn't "break" the conduit run, so if you are going from panel-12" - LR - 24" - J-box, you do not have a nipple of 24" or less. You have a conduit run of 36" + whatever the length of the LR is, and you will be subject to the rules of conduit fill and derating.
Does the 24" rule apply again if you "break" the run with a junction box instead of a conduit body?

Example: Panel 24" to junction box, Junction box 24" to another junction box? Would the rule apple to both the first and the second junction box in this example?

I am not going to do this, but just for clarity, if you had a say 10' conduit run, but you had junction boxes every 24", you would not have to derate?

Thanks
Jamie
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Old 02-27-2009, 10:03 AM   #7
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24" conduit rule derrating does not apply


Quote:
Originally Posted by InPhase277 View Post
Jamie, I agree that what you describe is actually 36", not 24. But if you have a 24" nipple, not only does derating not apply, but according to Chaper 9 Note 4, you can fill up to 60% of the cross-sectional area.
Thanks, I was aware of the 60% fill rule, I think I am using that rule, as I think I am 1 conductor over in one of my half inch conduits from a box to the panel. :-)

The problem I am having is that my panel is on the far side of the basement, so to get anywhere with conduit, I end up having to go up from the panel into the joist space for about 20', then drop below the joist space for 20', then get back up into the joist space again. I can't run below the joists, because duct works run across the entire room, and I already have to duck a little for the ducts. .

I am mainly trying to figure out a good way to get up into some other joists cavities without having to put 200 degrees of bends into each conduit to get up there. Hence my idea with doing 1 or 2 of these junction boxes to help avoid some of the tricky bends. (Plus I think it would make for a much cleaner panel setup to only have 1 or 2 conduits coming out of a panel.

Thanks
Jamie
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Old 02-27-2009, 10:06 AM   #8
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24" conduit rule derrating does not apply


Quote:
Originally Posted by jamiedolan View Post
Thanks, I was aware of the 60% fill rule, I think I am using that rule, as I think I am 1 conductor over in one of my half inch conduits from a box to the panel. :-)

The problem I am having is that my panel is on the far side of the basement, so to get anywhere with conduit, I end up having to go up from the panel into the joist space for about 20', then drop below the joist space for 20', then get back up into the joist space again. I can't run below the joists, because duct works run across the entire room, and I already have to duck a little for the ducts. .

I am mainly trying to figure out a good way to get up into some other joists cavities without having to put 200 degrees of bends into each conduit to get up there. Hence my idea with doing 1 or 2 of these junction boxes to help avoid some of the tricky bends. (Plus I think it would make for a much cleaner panel setup to only have 1 or 2 conduits coming out of a panel.

Thanks
Jamie
Can you drop BELOW the duct work? You could use some strut and suspend it from threaded rod to build a rack below the duct work, and you could run the pipes with out alot of bend.
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Old 02-27-2009, 10:09 AM   #9
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24" conduit rule derrating does not apply


Quote:
Originally Posted by jamiedolan View Post

I am not going to do this, but just for clarity, if you had a say 10' conduit run, but you had junction boxes every 24", you would not have to derate?

Thanks
Jamie
Yes, the wording of Note 4 in Chapter 9 would seem to allow this, but if I were an inspector, and saw this, I would have to argue that it is not the intent of the code.
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Old 02-27-2009, 10:18 AM   #10
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24" conduit rule derrating does not apply


Quote:
Originally Posted by InPhase277 View Post
Can you drop BELOW the duct work? You could use some strut and suspend it from threaded rod to build a rack below the duct work, and you could run the pipes with out alot of bend.
The ceilings total are only 7' and duckwork drops down right about 1'. So I would have to be down below 6' with the conduit. I can picture what you mean with the rack, and would love to do that if I had higher ceilings.



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Old 02-27-2009, 10:26 AM   #11
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24" conduit rule derrating does not apply


Quote:
Originally Posted by InPhase277 View Post
Yes, the wording of Note 4 in Chapter 9 would seem to allow this, but if I were an inspector, and saw this, I would have to argue that it is not the intent of the code.
If it was used in a manner to reach out to say 1 additional junction boxes in each direction (to reach other joist cavities) do you feel that is within the intent of the code?


i.e.
panel 24" to junction box Left side of junction box 24" to Junction box, Right side of junction box 24" to junction box.

A setup like that would allow me to access 3 joist cavities with an unlimited number of circuits running out.

(I need to terminate about 8 20A circuits for the kitchen, oven conduit, hot tub conduit, conduit for my sub panel and a conduit for my coffee equipment.) I just don't want this to look like a stupid mess of emt hitting that panel.

I almost wonder if I should yank out the pushmatic and put another CH panel there so I have an additional box to work off of.

Jamie

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