DIYbanter - View Single Post - When (if ever) can 14ga wire be used with 20A circuit breaker?

wrote:
On Fri, 10 Feb 2006 08:18:11 -0500, dnoyeB
wrote:

wrote:

On Thu, 09 Feb 2006 08:41:35 -0500, dnoyeB
wrote:

Open your electric water heater some day, you will have at least #10
feeding
#12.
It is inside a UL listed and labeled appliance, there for ok doky.

Yeah, I noticed mine is. I presumed that was because the #12 wires are THHN
and between two things rated for higher temperatures. No?
Still, it seemed like a foolish place to save $0.02.

If the wires melt and burn within the water heater housing, what is the
end result?

--
Thank you,

A 4500w water heater only pulls 18.75a. There is plenty of safety
factor in a #12 as a "fixture wire" but if it is protected by a 30a
breaker the "branch circuit" conductors must be #10.

if it only pulls 18.75a, why not put 12 everywhere? Protection is not
tied to the loading of the appliance, its tied to what happens under
failure conditions. If that appliance fails with a resistive short, it
can pull up to the load allowed by the circuit protection.

More likely they ensure that melted and burned wires wont start a fire
within the appliance. And that the appliance is obviously bad anyway so
loosing some wiring is not a significant penalty. You dont want to
loose wiring in your wall due to a bad appliance.

So 12 is not 'safe' in terns of it not failing, but in that if it does
fail, its not goign to cause any additional significant damage.

You notice I said the "branch circuit" conductors ARE required to be
#10 (when using a 30a breaker). If you are not happy with what a
recognized testing lab says is OK under the covers of listed
equipment, you will have to take it up with them. I'm sure a testing
lab would point you to facts about exactly how much temperature rise
you actually get in 12ga wire with a 30a load. It is far from being
enough to damage a 90c conductor.

You misread my post. I didn't say it was not OK within the appliance.
What I said was that it was OK, *not* due to the fact that it wont burn,
but to the fact that it wont cause a fire when/if it does.

Just because you can put a 12Ga wire on a circuit within an appliance
does not mean you can do that outside of the appliance.

--
Thank you,

"Then said I, Wisdom [is] better than strength: nevertheless the poor
man's wisdom [is] despised, and his words are not heard." Ecclesiastes 9:16