|
Posted by Doug Miller on December 12, 2006, 6:37 am
Klipstein) wrote:
> wrote:
> Klipstein) wrote:
>>>>Don Klipstein wrote:
>>>>
>>>>> Since resistance increases with temperature, actual ampacity does not
>>>>> increase much with an increase in temperature rating. And ampacity
>>>>> according to the code does not increase at all.
>>>>
>>>>I'm going to have to disagree with that.
>>>>
>>>>For simplicity, look at the "single conductor in free air" tables. (The
>>>>other tables show it too, just the absolute values are lower.)
>>>>
>>>>With 60-90C rated insulation, a #14 wire is rated for 20A. With
>>>>110-125C rated insulation, that same size wire is rated for 40A. If you
>>>>go up to 200C insulation, you can put 45A through it.
>>>
>>> Somehow, I suspect that upgrading from 110 or 125 C insulation to 200 C
>>>insulation only improving ampacity from 40 to 45 amps supports my point!
>>
>>Quite the opposite: it clearly contradicts your assertion that it "does not
>>increase at all".
>
> I did state that my "does not increase at all" was a code matter,
Yes, you did -- and I have repeatedly pointed out that this is not correct,
that the Code absolutely does recognize increased ampacity with increasing
conductor temperature.
The entire Code is online here:
http://nfpa-acs-01.gvpi.net:8080/rrserver/browser?title=/NFPASTD/7005SB
I refer you to Table 310.16.
>on
>which I would concede on appliance cords but I insist remains the case
>with romex.
You're commenting in a vacuum, based on a lack of knowledge. Read the Code.
You're wrong.
>
>> And, of course, the difference between 20A at 60 deg and 40A
>>at 125 deg makes that contradiction even more clear.
>
> So you have cited a data point opposing my point as well as a data point
>supporting my point (200C single conductor in free air good for 45 amps).
Read the Code. You're wrong. Table 310.16.
>
>>> Meanwhile, also consider that wiring in a building is usually not single
>>>conductor in free air, but 2 at least current-carrying conductors close to
>>>each other and heating each other up with a sheath around them and the
>>>environment outside the sheath usually not being "free air".
>>
>>That was just an example -- and maybe not a real good one. But it does show
>>that (not to put too fine a point on it) you don't know what you're talking
>>about when you say that "ampacity according to the code does not increase at
>>all".
>>
>>That's just not true.
>
> Sure is true with most wiring, such as permanently installed wiring!
>Code says 15 amps for AWG 14 regardless of temperature rating for
>permanently installed wiring!
Read the Code. You're wrong. Table 310.16.
>
>>See NEC Table 310.16 for abundant proof that the ampacity of a
>>conductor -- ANY conductor, ANY size -- absolutely DOES increase with
>>increasing temperature rating of the insulation.
>
> I google for that and find a nice chart:
>
>http://www.houwire.com/products/technical/article310_16.html
>
> I see close to the top a line entry for 14 AWG, with no ampacities being
>the 15 amps for 14 AWG permanently installed wiring, and I have already
>conceded on the specific issue of appliance cords. Along with this chart
>showing higher ampacities for specific cable types of which I think 97% or
>so is not "permanently installed wiring". In addition, the code's limits
>for "permanently installed wiring" do not appear to me to be increased
>above 15 amps for 14 AWG or 20 amps for 12 AWG on the basis of such wiring
>being allowed for "permanently installed wiring" (most of these cable
>types are not) and such cable types having special ampacity higher than 15
>amps for 14 AWG and 20 amps for 12 AWG.
>
Read the Code. You're wrong. Table 310.16.
>>> Add to this the fact that extra high temperature rating wire is used
>>>more where ambient temperature is higher, and I see good reason for AWG 14
>>>romex to be only allowed by code to be used in circuits up to 15 amps
>>>regardless of temperature rating.
>>
>>That's a completely separate issue from the ampacity of the wire, which Code
>>specifies as being, for example, 25A with THHN insulation.
>
> But does the Code allow AWG 14 with THNN insulation to be used in
>permanently installed wiring in a building in circuits protected by fuses
>or breakers of more than 15 amps?
No -- but that's because the Code builds the "80% rule" into the overcurrent
protection limits for 10, 14, and 12ga conductors, not because of any limits
on the conductor's ability to carry current. It's for additional safety. But
if you would actually READ THE CODE, you'd find out that the ampacities are in
fact considerably higher than the permitted overcurrent protection. It's two
separate issues.
> Since I conceded on appliance cords, I still consider the issue of
>permanently installed wiring to be valid!
Read the Code. You're wrong. Table 310.16.
>
>>In a separate
>>article, Code limits the overcurrent protection for 14 and 12 ga conductors to
>>15 and 20 amps, respectively, despite their having a higher ampacity.
> Starting to sound like what I am saying, especially in terms of code?
No, it's NOT starting to sound like what you're saying. You said that,
according to Code, conductor ampacity "does not increase at all" with
increased conductor temperature rating, and that simply is not true. Not for
fixture wires. Not for appliance cords. Not for permanently installed wiring.
Not true at all.
READ THE CODE.
Table 310.16.
--
Regards,
Doug Miller (alphageek at milmac dot com)
It's time to throw all their damned tea in the harbor again.
| 
Yahoo! 
Google 
Windows Live 
del.icio.us 
digg 
Netscape 
XML Sitemap