DIYbanter - View Single Post - Using #14 wire for one light on 20A breaker

Doug Miller

In article , (Don Klipstein) wrote:
In , Doug Miller wrote:
In ,marad :

I'm just curious how the code views that?

As a violation.

For example, if I but a common house type ceiling
fixture, they generally have 8 inches or up to several feet (on a
chandlier) of #14 standed wire as part of the fixture. So, if I am
running a 20A circuit I am already using #14 in the circuit.

Fixture wires generally have a much higher temperature rating than supply
wires, which enables them to carry higher current on smaller wires.

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.

Example: for copper wire, #8 TW has an ampacity of 40 amps; #8 THHN has an
ampacity of 55 amps.

Another example: #18 copper wire is permitted to carry 14 amps, IF it has 90
deg C insulation (e.g. THHN or THHW).

And ampacity
according to the code does not increase at all.

This simply is not true. See NEC Table 310.16 for abundant proof that the Code
absolutely does recognize increased ampacity for increased temperature
ratings.

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

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