4 14 nmb through 1 drilled hole

[Fred B]

and how is the math applicable Fred?

consider 376.22 , why does the NEC do '30', and the CEC '200'?

~RJ~

So if reading that section correctly, need to calculate the cross sectional area, free space has to be atleast 80% of the hole. Where is the reference in the code that gives the cross sectional value of NM cable? Thought there was a reference that showed that but can't find it, see table 5 but don't see NM listed.

 

[romex jockey]

So if reading that section correctly, need to calculate the cross sectional area, free space has to be atleast 80% of the hole. Where is the reference in the code that gives the cross sectional value of NM cable? Thought there was a reference that showed that but can't find it, see table 5 but don't see NM listed.

Good Q Fred
~RJ~

 

[don_resqcapt19]

334.80 referrers to table 310.15(B)(3)(a) Don

in one passage it accepts the exception to Table 310.15(B)(3)(a)., in the other it claims 310.15(A)(2), does not apply

310.15(B)(3)(a) Adjustment Factors.

(a) More Than Three Current-Carrying Conductors. Where the number of current-carrying conductors in a raceway or cable exceeds three, or where single conductors or multiconductor cables are installed without maintaining spacing for a continuous length longer than 600 mm (24 in.) and are not installed in raceways, the allowable ampacity of each conductor shall be reduced as shown in table 31o.15(B)(3)(a).

some clarity would be appreciated

thx

~RJ~

The rule for ampacity adjustment where the NM is run through a foam filled hole specifically and intentionally does not refer to section 310.15(B)(3)(a), it only refers to the Table that has the same number. This was written that way to require the ampacity adjustment anytime the NM is run through a foam filled hole of any length.

This rule first appeared in the 2005 code, but because of the exception in 310.15(A)(2), there really was no requirement to adjust the ampacity where the NM was installed in a foam filled hole. Because the original rule was not enforceable, the 2008 code added that language that prohibited the use of the exception in 310.15(A)(2)

 

[romex jockey]

The rule for ampacity adjustment where the NM is run through a foam filled hole specifically and intentionally does not refer to section 310.15(B)(3)(a), it only refers to the Table that has the same number. This was written that way to require the ampacity adjustment anytime the NM is run through a foam filled hole of any length.

This rule first appeared in the 2005 code, but because of the exception in 310.15(A)(2), there really was no requirement to adjust the ampacity where the NM was installed in a foam filled hole. Because the original rule was not enforceable, the 2008 code added that language that prohibited the use of the exception in 310.15(A)(2)

why would anyone wish to use any table , excluding the code content referring to it Don?

this here>>>

Where more than two NM cables containing two or more
current-carrying conductors are installed, without maintaining
spacing between the cables, through the same opening in wood
framing that is to be sealed with thermal insulation, caulk, or
sealing foam, the allowable ampacity of each conductor shall
be adjusted in accordance with Table 310.15(B)(3)(a) and the
provisions of 310.15(A)(2), Exception, shall not apply.



vs this here>>>

Where more than two NM cables containing two or more
current-carrying conductors are installed in contact with ther‐
mal insulation without maintaining spacing between cables, the
allowable ampacity of each conductor shall be adjusted in
accordance with Table 310.15(B)(3)(a).

reads like we can run rx all day long through 'thermal insulation' until we pass through a 2x4 stud

~RJ~

 

[infinity]

reads like we can run rx all day long through 'thermal insulation' until we pass through a 2x4 stud

~RJ~

It's pretty straightforward, if the stud hole is filled then derating applies for more than two NM cables.

 

[winnie]

IMHO the code text is very clear, but it seems to suggest that different physics applies two the various situations that Romex Jockey has pointed out (few conductors for a few inches in a stud with insulation vs many conductors in a sleeve coming out of a panel). They are _different_ situations, but it seems that in one situation code is overly restrictive and in the other code is overly permissive.

-Jon

 

[infinity]

This requirment was added to the code when someone tested several cables in a filled hole and found under specific conditions the temperature of the conductors can exceed the 90° C rating. In the real world this will almost never happen.

 

[kwired]

Whenever it was that they added this rule for the sealed holes and derating- I happened to go to CEU class given by an instructor at community college where they teach this trade. We talked a little about this rule in the class and he showed us a setup he had his students make up in the lab. They ran some cables through some bored holes some not sealed some were sealed same number and same load on them. They placed temp sensors in the holes and found the sealed holes did have somewhat significant rise in temperature vs the open holes. Been long enough ago I don't remember how much but do remember it was enough to make you think about what was going on there.

That said I believe they had near max permissible load on the conductors - it was resistance heating and I believe it took several hours to get the temperatures they did - conditions not so likely to occur in typical dwelling yet not impossible.

 

[david luchini]

334.80 referrers to table 310.15(B)(3)(a) Don

in one passage it accepts the exception to Table 310.15(B)(3)(a)., in the other it claims 310.15(A)(2), does not apply

It doesn't accept the exception to Table 310.15(B)(3)(a).

If 334.80 had referenced 310.15(B)(3), then the language in 310.15(B)(3) would apply. But 334.80 doesn't reference 310.15(B)(3), it specifically references Table 310.15(B)(3)(a).

 

[don_resqcapt19]

why would anyone wish to use any table , excluding the code content referring to it Don?

this here>>>

Where more than two NM cables containing two or more
current-carrying conductors are installed, without maintaining
spacing between the cables, through the same opening in wood
framing that is to be sealed with thermal insulation, caulk, or
sealing foam, the allowable ampacity of each conductor shall
be adjusted in accordance with Table 310.15(B)(3)(a) and the
provisions of 310.15(A)(2), Exception, shall not apply.

As I said that was a very intentional code reference as they wanted to require the ampacity adjustment for any length of NM run through a foamed hole. If they referenced the section, then the rule would not apply. By only referencing the table, the rule always applies to NM installed in a foamed hole.

vs this here>>>

Where more than two NM cables containing two or more
current-carrying conductors are installed in contact with ther‐
mal insulation without maintaining spacing between cables, the
allowable ampacity of each conductor shall be adjusted in
accordance with Table 310.15(B)(3)(a).

reads like we can run rx all day long through 'thermal insulation' until we pass through a 2x4 stud

~RJ~

In this case they intend to apply the rules of both the actual code section and the table, as well as permitting the use of the exception to 310.15(A)(2).
As I recall the substantiation for the foamed holes and the contact with thermal insulation were different with the one for the foamed hole showing a temperature rise high enough to be of concern even in a very short length and the thermal contact one did not show that.

Also in both cases, there is no real world impact until you have a total of 10 current carrying conductors installed together.