Need to know how to calculate T-body fill factor for this situation: All attached conduits are within fill factor, and any cross-sectional slice through the T is within fill factor, but summing all entering/exiting conductor cross-sectional areas and dividing by 2 is over. Specifically, 9 conductors in the side entry, 3 go left 6 go right, then an additional 3 pass through from left to right. No cross section intersects more than 9, the sum of whose cross-sectional areas is within the fill factor. What does the code require? (Easy to define what "conductor passing through the body" means for an LB, not so clear for a T.)
Code calculation for T-body fill factor
- Thread starter BcatV
- Start date
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Starts with the conductor size but if they're #6 or smaller then you just need to be concerned with the fill of each raceway attached to the T conduit body.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Then the 6X and 8X rules in 314.28 would apply.
Since essentially no Ts or LBs would meet the 6x or 8x rule, I am assuming that 314.28(A)(3) applies, which leads me back to my original question of how to correctly count the conductors to calculate compliance with the listed volume/total conductor cross-sectional area?
- Location
- New Jersey
- Occupation
- Journeyman Electrician
There is no volume or total conductor calculation for the conductor sizes you've mentioned. The requirement is for the proper 6X or 8X distance between the entries to ensure that the conductors do not get damaged during installation. For conductors smaller than #4 AWG different rules would apply.
Thanks Infinity, I appreciate your input, and the safe-pulling-radius to protect the conductors is logical, and yet, Ts and LBs exist, and the max-conductor allowances are marked in the bodies, for instance 3 - 2/0 in the one I'm looking at, which seems to imply that one could route up to 3 2/0 conductors through, even though the body doesn't come close to the 6X or 8X rule for the 2inch conduit entries.
314.28(A)(3) Smaller Dimensions. Listed boxes or listed conduit bodies of dimensions less than those required in 314.28(A)(1) and (A)(2) shall be permitted for installations of combinations of conductors that are less than the maximum conduit or tubing fill (of conduits or tubing being used) permitted by Table 1 of Chapter 9.
Listed conduit bodies of dimensions less than those required in 314.28(A)(2), and having a radius of the curve to the centerline not less than that indicated in Table 2 of Chapter 9 for one-shot and full-shoe benders, shall be permitted for installations of combinations of conductors permitted by Table 1 of Chapter 9. These conduit bodies shall be marked to show they have been specifically evaluated in accordance with this provision.
Where the permitted combinations of conductors for which the box or conduit body has been listed are less than the maximum conduit or tubing fill permitted by Table 1 of Chapter 9, the box or conduit body shall be permanently marked with the maximum number and maximum size of conductors permitted.
Hard to see how this body or others could meet the Table 2 bend radii, so the markings consistent with the last paragraph seem to imply approval even though it doesn't meet the bend radii. Are conduit bodies like this used for conductors as large as the markings?
314.28(A)(3) Smaller Dimensions. Listed boxes or listed conduit bodies of dimensions less than those required in 314.28(A)(1) and (A)(2) shall be permitted for installations of combinations of conductors that are less than the maximum conduit or tubing fill (of conduits or tubing being used) permitted by Table 1 of Chapter 9.
Listed conduit bodies of dimensions less than those required in 314.28(A)(2), and having a radius of the curve to the centerline not less than that indicated in Table 2 of Chapter 9 for one-shot and full-shoe benders, shall be permitted for installations of combinations of conductors permitted by Table 1 of Chapter 9. These conduit bodies shall be marked to show they have been specifically evaluated in accordance with this provision.
Where the permitted combinations of conductors for which the box or conduit body has been listed are less than the maximum conduit or tubing fill permitted by Table 1 of Chapter 9, the box or conduit body shall be permanently marked with the maximum number and maximum size of conductors permitted.
Hard to see how this body or others could meet the Table 2 bend radii, so the markings consistent with the last paragraph seem to imply approval even though it doesn't meet the bend radii. Are conduit bodies like this used for conductors as large as the markings?
- Location
- New Jersey
- Occupation
- Journeyman Electrician
If the conduit body is marked for (3)-#2/0 you can install (3)-#2/0 even if it does not meet the 6X or 8X rule. This is becuase the manufacturer has determined that following the conductor information stamped on the conduit body will still allow the conductors be installed without being damaged.
- Location
- Illinois
- Occupation
- retired electrician
314.28(A)(3)......
For other conductor sizes and combinations, the total cross-sectional area of the fill shall not exceed the cross-sectional area of the conductors specified in the marking, based on the type of conductor identified as part of the product listing.
Informational Note:
Unless otherwise specified, the applicable product standards evaluate the fill markings covered here based on conductors with Type XHHW insulation.
Exactly, which brings us full circle to my original question, how to count/calculate the conductors to sum up: "All attached conduits are within fill factor, and any cross-sectional slice through the T is within fill factor, but summing all entering/exiting conductor cross-sectional areas and dividing by 2 is over. " I actually calculated this for only the conductor cross-sectional areas, not including the insulation, so I'll have to recalculate, but the basic question remains, does one add up all entering/exiting wire areas then divide by 2, or does one use the cross section of the body that has the most conductors passing through it, since different parts of the T, unlike an L, can have different numbers of conductors passing through. See the attached image for the exact layout I would like to calculate.
Thanks to all who gave this a thought!
Thanks to all who gave this a thought!
Attachments
- Location
- New Jersey
- Occupation
- Journeyman Electrician
The cubic inch volume is not relevant but the conductor information {(3)-#2/0} stamped into the conduit body is. Since your conductors are all smaller than #2/0 you would need to find and not exceed the equivalent of (3)-#2/0 at any pull point.
So think of it as you can install (3)-#2/0 in this conduit body or any other combination of smaller conductors not exceeding the stamped maximum of (3)-#2/0.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
#2 thwn is .1333sq.in
3 x .1333 = .3999 sq. in
Any combination of conductions smaller than or equal to #2 must not be over .3999 sq. in
I believe that would be acceptable
3 x .1333 = .3999 sq. in
Any combination of conductions smaller than or equal to #2 must not be over .3999 sq. in
I believe that would be acceptable
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
The OP's question is only relevant for a conduit body with 3 or more hubs. And then it boils down to this:
Say I have T conduit body with openings A, B, and C. And I have 2 wires going from A to B, 2 wires going from A to C, and 2 wires going from B to C. So three are 6 different wires present in the conduit body, but at any cross section anywhere, there are only 4 wires. [Assume the two pairs of wires exiting the middle hub don't cross each other before exiting.]
In applying 314.28(A)(3), do I use a count of 4 wires, or a count of 6 wires?
Cheers, Wayne
Say I have T conduit body with openings A, B, and C. And I have 2 wires going from A to B, 2 wires going from A to C, and 2 wires going from B to C. So three are 6 different wires present in the conduit body, but at any cross section anywhere, there are only 4 wires. [Assume the two pairs of wires exiting the middle hub don't cross each other before exiting.]
In applying 314.28(A)(3), do I use a count of 4 wires, or a count of 6 wires?
Cheers, Wayne
Last edited:
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
I seem to recall (but may be mistaken) that the listing standard for such labeling in conduit bodies is based on XHHW insulation.
Cheers, Wayne
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
I believe four, the greatest count in any one hub.
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
I agree, based on the last sentence of 314.28(A)(3): "For other conductor sizes and combinations, the total cross-sectional area of the fill shall not exceed the cross-sectional area of the conductors specified in the marking, based on the type of conductor identified as part of the product listing."
This refers to cross-sectional area of the fill, not the total number of conductors present in the conduit body.
Cheers, Wayne
- Location
- Illinois
- Occupation
- retired electrician
For the fill, I would look to 314.16(C)(1), even though we have conductors larger than 6 AWG. Based on that, as long as any of the conduits connected to the T do not exceed their permitted fill, the fill in the T is fine. However that does not address the issue of pulling large conductors through the T.
So the actual fill is based on 314,16(C)(1), but you must also comply with 314.28(A)(3) because we have conductors larger than 6 AWG. The calculation in (A)(3) may result in a lesser fill than than permitted
by 314.16(C)(1).
I had a PI to delete "Boxes and conduit bodies enclosing conductors 4 AWG or larger shall also comply with 314.28. Outlet and device boxes shall also comply with 314.24." in the parent text of 314.16 because that is covered by 314.28.
That was rejected with a panel statement that said you need to comply with both 314.16 and 314.28. I think this is an example of where you would apply both rules.
So the actual fill is based on 314,16(C)(1), but you must also comply with 314.28(A)(3) because we have conductors larger than 6 AWG. The calculation in (A)(3) may result in a lesser fill than than permitted
by 314.16(C)(1).
I had a PI to delete "Boxes and conduit bodies enclosing conductors 4 AWG or larger shall also comply with 314.28. Outlet and device boxes shall also comply with 314.24." in the parent text of 314.16 because that is covered by 314.28.
That was rejected with a panel statement that said you need to comply with both 314.16 and 314.28. I think this is an example of where you would apply both rules.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Does it matter? The condition that is addressed is when pulling from one entry to the other can you comply with the marking on the conduit body. So if you had A, B, and C entries the conductors coming out of one entry and entering the other have to comply with either the 6X rule for an angle pull or a calculation using the markings on the conduit body. Either method is designed to ensure that the conductor won't be damaged during installation.