Ampacity of Bare and convered conductor

[Son]

Hi all;

In table 310.21 NEC, with the same size, temperature, ampacities of Bare conductors are smaller than convered conductors.

But

I think that when a conductor is not covered, it will not be affected by temperature of insulation, so why is the ampacity of Bare conductor smaller ?

I don't understand why.
Please, explain to me clearly.

Tks.
Son

 

[glene77is]

Son,
Good question,
but, this thread might be more appropriate for the "Calculation/Engineering" forum.

Consider the surface corrosion, and the irregular surface presented to major electron flow. Insulation inhibits this condition.

Now, let's see what others have to say. I am curious also.

 

[Son]

I have posted this question in "Calculation/Engineering" forum.

I don't think nobody in NEC could explain why. Maybe some are busy for other work.

I'm waiting for answering...

Thank you Glene77is.

 

[iwire]

I have posted this question in "Calculation/Engineering" forum.

.

Which is why I am closing this one.

Bare and coverd conductors