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Using #14 wire for one light on 20A breaker maradcliff 12-11-2006
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Posted by on December 11, 2006, 11:00 pm


On Tue, 12 Dec 2006 00:37:11 GMT, spambait@milmac.com (Doug Miller)
wrote:


>> Since resistance increases with temperature, actual ampacity does not
>>increase much with an increase in temperature rating.
>
>The temperature rating of a conductor depends on its *insulation*, not the
>conductor itself. Ampacity *does* increase substantially with an increase in
>temperature rating, due to the ability of the insulation to withstand a higher
>conductor temperature.

This whole issue really doesn't have anything to do with the ampacity
of the wire. 310.16 says #14 is good for 20a at 60c,. This is really a
240.4(D) issue which builds the "80% rule" into the code for "small
conductors". I agree 100% it is a code violation but since a single
lampholder is a fixed load of 250w or less I can't see this as being
the worst violation I have seen and I wouldn't lose any sleep over it.
If he later put a receptacle up there he would be moving into that
"uncontrolled load" territory 240.4(D) was written for. It forces the
80% limit with a lower rated breaker than the wire ampacity can
support and he is losing that protection

Posted by Chris Friesen on December 11, 2006, 7:47 pm


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.

Chris

Posted by Don Klipstein on December 11, 2006, 10:33 pm


>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!

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".

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.

- Don Klipstein (don@misty.com)

Posted by Doug Miller on December 11, 2006, 10:58 pm


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". And, of course, the difference between 20A at 60 deg and 40A
at 125 deg makes that contradiction even more clear.
>
> 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.

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.
>
> 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. 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.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.

Posted by Don Klipstein on December 12, 2006, 12:11 am


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, on
which I would concede on appliance cords but I insist remains the case
with romex.

> 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).

>> 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!

>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.

>> 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?
Since I conceded on appliance cords, I still consider the issue of
permanently installed wiring to be valid!

>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?

>--
>Regards,
> Doug Miller (alphageek at milmac dot com)
>
>It's time to throw all their damned tea in the harbor again.

- Don Klipstein (don@misty.com)

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