Over 30 current carrying conductors in a wireway

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Jpflex

Jpflex

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How is this rule applied for derating ampacity for over 30 current carrying conductors in a wire way?


Do you derate only the number of current carrying conductors over 30 such as 35 current carrying conductors = 35 - 30 ccc = 5 conductors x 0.80% ampacity of 90 degree insulation ampacity or


35 current carrying conductors x 0.40 % ampere reduction based on table 310.15 b?
 
roger said:
What do you think?
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I think it would be stupid to reduce 35 conductors to 80% ampacity

But have 30 conductors at 100% ampacity but with just 5 wires more and have to reduce all wires to just 40% ampacity. 1 to 5 more wires over 30 isn’t going to add that much heat to require such a reduction

Reducing the 5 extra wires over 30 to 40% ampacity makes more sense to me and the code does say reduction applies only after 30 conductors

This can be used burpees in many different ways
 
Correction to above I meant reducing 35 conductors to just 40% of their ampacity at rated insulation

And 5 extra conductors over 30 for wire ways to just 80 percent of their ampacity
 
You apply the ampacity adjustment based on the total number of current carrying conductors, so in this example, it will be based on 35 conductors. However, you may be able to use the exception to 310.15(A)(2) or in 310.14(A)(2) in the newer codes.
 
don_resqcapt19 said:
You apply the ampacity adjustment based on the total number of current carrying conductors, so in this example, it will be based on 35 conductors. However, you may be able to use the exception to 310.15(A)(2) or in 310.14(A)(2) in the newer codes.
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Ok but it seems stupid that you can go 100% ampacity for 30 wires but add just one wire and all of a all 30 wires only have 40% ampacity
 
Jpflex said:
Ok but it seems stupid that you can go 100% ampacity for 30 wires but add just one wire and all of a all 30 wires only have 40% ampacity
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I believe there are a couple of tiers between 0 and 30 wires, like 70%.

Added: Okay, I now see wireway vs raceway.
 
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Note that the derating is for conductors in any one cross sectional area, not in the entire wireway.
(picture taking out a slice of wireway like you would a slice of bread)
Not too common an occurrence.
 
This entire 30 CCC concept is terrible. If you have 200' of wireway maybe it makes sense but in general that section should exclude any wireway less than a given dimension, say 10'.
 
O
infinity said:
This entire 30 CCC concept is terrible. If you have 200' of wireway maybe it makes sense but in general that section should exclude any wireway less than a given dimension, say 10'.
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Often that is what happens when you apply the exception to 310.15(A)(2) in the older codes or 310.14(A)(2) in the 2020 and 2023.
 
don_resqcapt19 said:
O

Often that is what happens when you apply the exception to 310.15(A)(2) in the older codes or 310.14(A)(2) in the 2020 and 2023.
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True but the exception has a 10' or 10% component which means if you have 10' of wireway your conductors need to meet the 10' or 10% which is not going to happen if you runs are less than 90'. This 30 CCC's rule for short sections of wireway should be removed to avoid having to do a cumbersome calculation. This is such a common violation yet buildings are not burning down.
 
augie47 said:
Note that the derating is for conductors in any one cross sectional area, not in the entire wireway.
(picture taking out a slice of wireway like you would a slice of bread)
Not too common an occurrence.
Click to expand...
O ok that makes better sense
 
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