Barrier in wireways and derating.

Status
Not open for further replies.
If any one was wondering how I came up with .0625.
Grounding,two threads based on 32 threads per inch and two threads required. 1/32= .03125 *2= .0625
 
Tulsa Electrician said:
Does the netural count as an ccc.
Are these stacked or bundled for more than 24".
Rough math on area is 8*8**.20
Around 12.8 you would need to subtract material thickness usually around .0625. That would give you 12.40. for total area allowed.
7.875*7.875= 12.403

You may only have 20 ccc if netural does not count.
If not stacked or bundled longer than 24" no derate.

Edit, you may be able to use the 10' 10% if bundled or stacked longer than 24"
Click to expand...
Should have been 7.875 x 7.875*.20=12.403
Sorry about that.
 

Attachments

  • Screenshot_20230706-193159.png
    Screenshot_20230706-193159.png
    101.1 KB · Views: 5
don_resqcapt19 said:
Would that make any real difference in the heat transferred to the other section?
Click to expand...
I wouldn't think so. My comment was based on the starting point of two touching side-by-side wireways, and what simple mechanical changes to that configuration of sheet metal would undisputably have no bearing on whether 30 CCCs should be allowed on each side without derating. Namely joining the two backpieces into a single piece of metal, and joining the two touching side walls into a single piece of metal (or not, the partition could be two pieces).

But on the physics, I don't see how a single full depth longitudinal partition in a wireway would behave differently from two touching side by side wireways.

Cheers, Wayne
 
don_resqcapt19 said:
Would that make any real difference in the heat transferred to the other section? I can see it changing the speed of transfer as it will take a bit more time to get the double thickness up to the maximum temperature it will achieve, but after that, I see the same amount of heat transfer between the sections.
Click to expand...
I think many of us are operating from the premise that this code is a little arbitrary and just trying to find a way around it. Not really concerned about actual heat transfer or wire heating up. It like the concept that 10 #12's require the same derating in a 4" conduit as they do in a 3/4" conduit.
 
Doesnt it kind of assume all of them might be fully loaded at the same time? Lets say I have 10 wires in the pipe and an amp down a pair of 14, another amp down a pair of 12 and 20 on a pair of 10 for 45 seconds every few minutes we still got to derate it,,, but I can cook on 9 wires just fine?
 
Tulsa Electrician said:
One item to remember with a wire way, it is a raceway.
Click to expand...
Yep.

I am not convinced the number of conductors has anything to do with the external heat transfer. The 30 count limit is not dependent on the cross section area of the wireway so it probably is related to the poor internal heat transfer of bundled conductors.
 
Tainted said:
Haven't gone far through the design yet, each 8x8 wireway will have 10 apartments. That's 30 CCC right there.
Click to expand...
I am looking at the exception to 310.14(A)(2) in the 2020 code or in 310.15(A)(2) in the 2017. Depending on the total length of the cables and the length the within wireway, ampacity adjustment may not be required.
 
wwhitney said:
I wouldn't think so. My comment was based on the starting point of two touching side-by-side wireways, and what simple mechanical changes to that configuration of sheet metal would undisputably have no bearing on whether 30 CCCs should be allowed on each side without derating. Namely joining the two backpieces into a single piece of metal, and joining the two touching side walls into a single piece of metal (or not, the partition could be two pieces).

But on the physics, I don't see how a single full depth longitudinal partition in a wireway would behave differently from two touching side by side wireways.

Cheers, Wayne
Click to expand...
So we need a rule to require separation between wireways :D
 
jim dungar said:
Yep.

I am not convinced the number of conductors has anything to do with the external heat transfer. The 30 count limit is not dependent on the cross section area of the wireway so it probably is related to the poor internal heat transfer of bundled conductors.
Click to expand...
I sort of eluded to that in a feeble attempt. Lots of other places are allowed to do a load calc, here, number of conductors. Conductors matched the breaker but are oversized for the load, as a "physics " matter cant see the hurt unless we really loaded every wire to 80%?
 
Sberry said:
I sort of eluded to that in a feeble attempt. Lots of other places are allowed to do a load calc, here, number of conductors. Conductors matched the breaker but are oversized for the load, as a "physics " matter cant see the hurt unless we really loaded every wire to 80%?
Click to expand...
Very few of the NEC requirements are based completely on "physics". Most rules include a very heavy dose of conservative 'in case of'. This is probably a good thing based on the amount of human nature that occurs in our line of work.
 
jim dungar said:
Very few of the NEC requirements are based completely on "physics". Most rules include a very heavy dose of conservative 'in case of'. This is probably a good thing based on the amount of human nature that occurs in our line of work.
Click to expand...
I think a lot of them stem from "Oops, that caused a fire! Let's write a rule to keep that from happening again..." If you compare a 1923 NEC to a 2023 version, that resulted in a lot more rules. But yes, mostly because of the "human nature that occurs in our line of work".
 
I think that, early on, when electrification was new, the code was as more about protecting the environment from the wiring than it was protecting the wiring from the environment.
 
Status
Not open for further replies.
Top