Pipe Fill Help

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michaeljmeuse

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Location
Edmond
I was rejected for a 2" EMT pipe. Help me understand why. The 2" EMT comes out of the panel and hits a junction box. I used it as a trunk line. In this pipe I have twenty-two #12 20amp circuits, two #10 30 amp circuits, 3 #6 for a 3-phase A/C and a #4 THHN for my ground. Now im fine on pipe fill but the inspector said I need to derate it. He basically told me all my breakers would have to be 10 amp breakers because of the amount of current. Could someone please help me understand how to calculate this. I know i should know it. Is there an easy fix? because this is going to be a nightmare. I'd have to run another trunk line up and over :/ but maybe thats the only solution. Thanks

Kindest Regards
Michael M
 
infinity

infinity

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Staff member
Location
New Jersey
Occupation
Journeyman Electrician
IMO the only fix is to run several more smaller conduits, pull out some of the existing condcutors and route them into the new conduits. In order to calculate the derating you'll need to know how many CCC's you have in the 2" EMT and take it from there.
 
jumper

jumper

Senior Member
Location
3 Hr 2 Min from Winged Horses
This is an excerpt from a post that Infinity/Rob wrote.


Here's some examples of when to count the neutral as a CCC:

208Y/120 volt system-different circuit types:

A)- 2 wire circuit w/ 1 ungrounded, 1 neutral = 2 CCC's
B)- 3 wire circuit w/ 2 ungrounded, 1 neutral = 3 CCC's
C)- 4 wire circuit w/ 3 ungrounded, 1 neutral = 3 CCC's*

Notes:
A)- A normal 2 wire circuit has equal current flowing in each of the circuit conductors so they both count as CCC's.
B)- In this circuit the neutral current will be nearly equal to the current in the ungrounded conductors so the neutral counts as a CCC
C)- In this circuit the neutral will only carry the imbalance of the current between the three ungrounded conductors so it is not counted as a CCC, with one exception, *if the current is more than 50% nonlinear then the neutral would count as a CCC.

120/240 volt system-different circuit types:

D)- 2 wire circuit w/ 1 ungrounded, 1 neutral = 2 CCC's
E)- 3 wire circuit w/ 2 ungrounded, 1 neutral = 2 CCC's

Notes:
D)- A normal 2 wire circuit has equal current flowing in each of the circuit conductors so they both count as CCC's.
E)- In this circuit the neutral will only carry the imbalance between the two ungrounded condcutors so the neutral is not counted as a CCC.
 
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iMuse97

iMuse97

Senior Member
Location
Chicagoland
michaeljmeuse said:
I was rejected for a 2" EMT pipe. Help me understand why. The 2" EMT comes out of the panel and hits a junction box. I used it as a trunk line. In this pipe I have twenty-two #12 20amp circuits, two #10 30 amp circuits, 3 #6 for a 3-phase A/C and a #4 THHN for my ground. Now im fine on pipe fill but the inspector said I need to derate it. He basically told me all my breakers would have to be 10 amp breakers because of the amount of current. Could someone please help me understand how to calculate this. I know i should know it. Is there an easy fix? because this is going to be a nightmare. I'd have to run another trunk line up and over :/ but maybe thats the only solution. Thanks

Kindest Regards
Michael M
Click to expand...

In electrical work there is no such thing as a trunk line because of the derating that your inspector mentioned. If you have more than three current-carrying conductors in a pipe, or bundled cables (ie. romex), you must derate them. Best practices include running your two 30A circuits together, run your 3P 50A?? by itself, and equipment grounds with each, as necessary and/or required. Typically, I would run 4-maximum 20A circuits in a conduit, thus not exceeding the 80% derating adjustment factor. This is good design because if the customer adds something (they always do), I don't have to install anymore pipe after the ceiling grid/drywall/finishing systems are installed. The additional circuit in the conduit will at worst move me to the 70% derating adjustment factor, which is still OK for the 20A breaker.

As I see it, you need seven conduits of 3/4" or 1", sized for the conductors you put in them. If your #4 ground was an equipment grounding conductor you will need to install separate ones for each conduit as required. However, if for some reason it was the grounding electrode conductor you will want to run that separately from these other runs, making a total of eight separate conduits.
 
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michaeljmeuse

Member
Location
Edmond
Thank you guys for the response. It makes sense now. Just a huge oversight :/ grrrr and a costly one. Oh well. At least I learned something from it
 
jumper

jumper

Senior Member
Location
3 Hr 2 Min from Winged Horses
iMuse97 said:
Typically, I would run 4-maximum 20A circuits in a conduit, thus not exceeding the 80% derating adjustment factor. This is good design because if the customer adds something (they always do), I don't have to install anymore pipe after the ceiling grid/drywall/finishing systems are installed. The additional circuit in the conduit will at worst move me to the 70% derating adjustment factor, which is still OK for the 20A breaker.
Click to expand...

Four 2 wire circuits would be at 70%, and fifth would be 10 CCCs derated to 50%.
 
D

defears

Senior Member
Location
NJ
Leave the 2" and pull 4 4wire circuits in #10. Still leaves you with one spare. Then you just need to pipe 2 3/4".
 
C

CAPS

Member
Your installation method is commonly done but your "trunk line" has to be a nipple no longer than 24 inches see Chapter 9 Note 4. This allows you to get many circuits out of the panel to a junction box for distribution. Max fill is 60% with no derate for number of conductors.
 
Little Bill

Little Bill

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Staff member
Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
jumper said:
[/B] Always trying to learn. Why does this matter in this application?
Click to expand...
I'm having "frozen brain syndrome" this morning but I'm thinking of something that says something about conduit being at least 18" but not more than 6' being used as protection, but I can't find it. Help!!! Why aren't the smileys working?
 
jumper

jumper

Senior Member
Location
3 Hr 2 Min from Winged Horses
Found it. I always forget about this one, never applied it myself.

310.15(2) Selection of Ampacity. Where more than one ampacity
applies for a given circuit length, the lowest value shall be
used.
Exception: Where two different ampacities apply to adjacent
portions of a circuit, the higher ampacity shall be permitted to
be used beyond the point of transition, a distance equal to 3.0
m (10 ft) or 10 percent of the circuit length figured at the
higher ampacity, whichever is less.
 
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