I have numerous conduits entering the electrical room that are going to numerous panels in the room, approx. 200 ccc's. Some conduits have ccc's that go to more than one panel so a 12x12 trough was installed over the panels. The field conduits enter the trough and the ccc's split into their designated panels. Each panel has sufficent number of nipples to the trough. All 20 amp circuits using #10 wire because of the field conduit fill derating. I have never had a inspection failure doing this and have seen 100's of similar installs. My PM insists that we must use the 366.22 (a) making the trough non compliant because of the well over 30 ccc's in the trough. Let me note that most of the ccc's pass directly into the panel below while other ccc's are diverted in the trough to their respected panels. My question is if this is the case then why have I not had a failure before and why is this method so common with these installs. Thanks.
Trough usage
- Thread starter Hoodood
- Start date
- Status
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Just because you were never called on it before does not mean that the install was compliant. It looks like over 30 conductors then de-rating is in order
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
366.22(A) makes it pretty clear the 20 percent fill applies at any cross section, but the 30 conductor rule isn't worded as clearly, but you would think it intends to mean at any cross section as well. It doesn't take much to reach 30 conductors, but if they all come and go at different locations you still have some diversity in the heating effects, where if you ran all contained conductors the length of the gutter you have a situation more similar to what you have in a raceway, and all cross sections contain all the same thing.
- Location
- Massachusetts
You could have a 1,000s of CCCs in the total length of trough and not have to derate unless there is more than 30 CCCs in one cross section.
So if the circuits mostly go straight through the trough and not down the length ofi it you should be fine.
So if the circuits mostly go straight through the trough and not down the length ofi it you should be fine.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
This is a very common installation practice and often results in the derating violation but no one seems to care. As mentioned you count the CCC's at a cross section.
If a large junction box of the exact same dimensions were used there wouldn't be an issue. IMO someone needs to re-write this part of the wireway Article to make it reflect real world installations that aren't ever going to be a problem. Rant over. :roll:
OK, then how is the cross sectional usage determined. If most ccc's are going straight into the panel and under 30 pass each other? Example, a trough has 42 circuits entering and passing into nipples into the panell because in some cases it's nearly impossible to land these cables all into the top of the panel. You are saying that all those circuits are falling into the over 30 rule which would mean you need to increase wire size significantly. If so how does this not apply to the gutter space inside panels?
Joe Villani
Senior Member
- Location
- Westchester County NY
Take a look at 310.15(A)(2) Exception
Where two different ampacities apply to adjustment portions of a circuit, the higher ampacity shall be permitted to be used beyond the point of transition, a distance equal to 10 feet or 10 percent the circuit length figured at the higher ampacity, whichever is less.
Based on your install this might give you relief.
Joe Vilani
Where two different ampacities apply to adjustment portions of a circuit, the higher ampacity shall be permitted to be used beyond the point of transition, a distance equal to 10 feet or 10 percent the circuit length figured at the higher ampacity, whichever is less.
Based on your install this might give you relief.
Joe Vilani
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
kind of sort of, but one longer wireway doing essentially the same thing might not be.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
IMO that doesn't apply to wireways.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Why? If you have one minimum ampacity in the wireway and another in a raceway leaving the wireway - if the circuit is long enough I don't see why it wouldn't apply.
It probably doesn't work out to be able to use it in most cases but is an option if conditions are right.
- Location
- Illinois
- Occupation
- retired electrician
In my opinion, that exception applies anywhere you are required to adjust or correct a conductor's ampacity.
Strathead
Senior Member
- Location
- Ocala, Florida, USA
- Occupation
- Electrician/Estimator/Project Manager/Superintendent
As to whether it is a good code, you are railing against the machine. As to this question.
If you were to slide a paper thin razor in a horizontal cross section (with power off
) Would it cut through 30 wires or more? Simple as that.
- Location
- Massachusetts
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
As to whether it is a good code, you are railing against the machine. As to this question.
If you were to slide a paper thin razor in a horizontal cross section (with power off
If the trough runs horizontally, why would you use a horizontal cross section?
It is not explicitly stated, but most analysis I have seen assumes that the cross section is perpendicular to the long dimension of the trough.
Requiring all cross sections (horizontal, vertical, front to back) to meet the 30 conductor limit seems pointless.
- Location
- Massachusetts
Not 'cross sectional' that is a medical and scientific term
Just cross section and when the NEC uses a word that they do not define we can go to the dictionary.
http://www.merriam-webster.com/dictionary/cross section
So pick any spot along the length of the wireway and count the conductors passing through an imaginary line across the wireway at a right angle to it's long dimension.
If any of those cross sections have more than 30 conductors you will need to apply derating to those conductors passing through that cross section.
- Location
- Massachusetts
Exactly, the rule makes no sense unless the cross section is perpendicular to the long dimension.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
What if the wireway is 12X12X12?
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Then you spent a lot of money on the wireway if all you have in it 30 or less 12 AWG conductors
Cow
Senior Member
- Location
- Eastern Oregon
- Occupation
- Electrician
I've gotten called on it before, it was 90 ccc's.:ashamed1: A lot of circuits, but not a lot of load.
Now I route my underground/overhead conduits as best as possible to the location where the panel will be. It used to be you'd run your underground conduit however it layed out the best in the dirt and then used the gutter to route the conductors where necessary. Now a guy has to pay a little more attention to the ccc's and where the conduits actually need to end up.
Worst case, I'm going to stack a gutter on top of a gutter with chase nipples between them every so often. Don't forget the 10% or 10' rule either, that can save you some grief too.
Now I route my underground/overhead conduits as best as possible to the location where the panel will be. It used to be you'd run your underground conduit however it layed out the best in the dirt and then used the gutter to route the conductors where necessary. Now a guy has to pay a little more attention to the ccc's and where the conduits actually need to end up.
Worst case, I'm going to stack a gutter on top of a gutter with chase nipples between them every so often. Don't forget the 10% or 10' rule either, that can save you some grief too.
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